Update version

Closes #135

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -1,4 +1,4 @@
-name: 🐞 Bug report
+name: 🐛 Bug report
 description: Report broken functionality.
 labels: [bug]
 
@@ -6,37 +6,70 @@ body:
   - type: markdown
     attributes:
       value: |
-      🧐 **Guidelines:**
+        - Avoid generic or vague titles such as "Something's not working" or "A couple of problems" — be as descriptive as possible.
+        - Keep your issue focused on one single problem. If you have multiple bug reports, please create a separate issue for each of them.
+        - Issues should represent **complete and actionable** work items. If you are unsure about something or have a question, please start a [discussion](https://github.com/Tyrrrz/CliFx/discussions/new) instead.
+        - Remember that **CliFx** is an open-source project funded by the community. If you find it useful, **please consider [donating](https://tyrrrz.me/donate) to support its development**.
 
-      - Search through [existing issues](https://github.com/Tyrrrz/CliFx/issues?q=is%3Aissue) first to ensure that this bug has not been reported before.
-      - Write a descriptive title for your issue. Avoid generic or vague titles such as "Something's not working" or "A couple of problems".
-      - Keep your issue focused on one single problem. If you have multiple bug reports, please create separate issues for each of them.
-      - Provide as much context as possible in the details section. Include screenshots, screen recordings, links, references, or anything else you may consider relevant.
-      - If you want to ask a question instead of reporting a bug, please use [discussions](https://github.com/Tyrrrz/CliFx/discussions/new) instead.
+        ___
 
   - type: input
     attributes:
       label: Version
-    description: Which version of CliFx does this bug affect?
-    placeholder: ver X.Y.Z
+      description: Which version of the package does this bug affect? Make sure you're not using an outdated version.
+      placeholder: v1.0.0
     validations:
       required: true
 
-- type: textarea
+  - type: input
     attributes:
-    label: Details
-    description: Clear and thorough explanation of the bug.
-    placeholder: I was doing X expecting Y to happen, but Z happened instead.
+      label: Platform
+      description: Which platform do you experience this bug on?
+      placeholder: .NET 7.0 / Windows 11
     validations:
       required: true
 
   - type: textarea
     attributes:
       label: Steps to reproduce
-    description: Minimum steps required to reproduce the bug.
+      description: >
+        Minimum steps required to reproduce the bug, including prerequisites, code snippets, or other relevant items.
+        The information provided in this field must be readily actionable, meaning that anyone should be able to reproduce the bug by following these steps.
+        If the reproduction steps are too complex to fit in this field, please provide a link to a repository instead.
       placeholder: |
         - Step 1
         - Step 2
         - Step 3
     validations:
       required: true
+
+  - type: textarea
+    attributes:
+      label: Details
+      description: Clear and thorough explanation of the bug, including any additional information you may find relevant.
+      placeholder: |
+        - Expected behavior: ...
+        - Actual behavior: ...
+    validations:
+      required: true
+
+  - type: checkboxes
+    attributes:
+      label: Checklist
+      description: Quick list of checks to ensure that everything is in order.
+      options:
+        - label: I have looked through existing issues to make sure that this bug has not been reported before
+          required: true
+        - label: I have provided a descriptive title for this issue
+          required: true
+        - label: I have made sure that that this bug is reproducible on the latest version of the package
+          required: true
+        - label: I have provided all the information needed to reproduce this bug as efficiently as possible
+          required: true
+        - label: I have sponsored this project
+          required: false
+
+  - type: markdown
+    attributes:
+      value: |
+        If you are struggling to provide actionable reproduction steps, or if something else is preventing you from creating a complete bug report, please start a [discussion](https://github.com/Tyrrrz/CliFx/discussions/new) instead.

.github/ISSUE_TEMPLATE/config.yml

@@ -1,8 +1,11 @@
 blank_issues_enabled: false
 contact_links:
-  - name: 💬 Discord server
-    url: https://discord.gg/2SUWKFnHSm
-    about: Chat with the project community.
+  - name: ⚠ Feature request
+    url: https://github.com/Tyrrrz/.github/blob/master/docs/project-status.md
+    about: Sorry, but this project is in maintenance mode and no longer accepts new feature requests.
   - name: 🗨 Discussions
     url: https://github.com/Tyrrrz/CliFx/discussions/new
     about: Ask and answer questions.
+  - name: 💬 Discord server
+    url: https://discord.gg/2SUWKFnHSm
+    about: Chat with the project community.

.github/ISSUE_TEMPLATE/feature-request.yml

@@ -1,22 +0,0 @@
-name: ✨ Feature request
-description: Request a new feature.
-labels: [enhancement]
-
-body:
-- type: markdown
-  attributes:
-    value: |
-      🧐 **Guidelines:**
-
-      - Search through [existing issues](https://github.com/Tyrrrz/CliFx/issues?q=is%3Aissue) first to ensure that this feature has not been requested before.
-      - Write a descriptive title for your issue. Avoid generic or vague titles such as "Some suggestions" or "Ideas for improvement".
-      - Keep your issue focused on one single problem. If you have multiple feature requests, please create separate issues for each of them.
-      - Provide as much context as possible in the details section. Include screenshots, screen recordings, links, references, or anything else you may consider relevant.
-      - If you want to ask a question instead of requesting a feature, please use [discussions](https://github.com/Tyrrrz/CliFx/discussions/new) instead.
-
-- type: textarea
-  attributes:
-    label: Details
-    description: Clear and thorough explanation of the feature you have in mind.
-  validations:
-    required: true

.github/workflows/main.yml

@@ -1,12 +1,28 @@
 name: main
 
-on: [push, pull_request]
+on:
+  workflow_dispatch:
+    inputs:
+      package-version:
+        type: string
+        description: Package version
+        required: false
+      deploy:
+        type: boolean
+        description: Deploy package
+        required: false
+        default: false
+  push:
+  pull_request:
 
 jobs:
   main:
     uses: Tyrrrz/.github/.github/workflows/nuget.yml@master
     with:
-      dotnet-version: 6.0.x
+      dotnet-version: 8.0.x
+      package-version: ${{ inputs.package-version }}
+      # Deploy only on tags by default, unless deploy is explicitly requested
+      deploy-on-tags-only: ${{ !(github.event_name == 'workflow_dispatch' && inputs.deploy) }}
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
       NUGET_TOKEN: ${{ secrets.NUGET_TOKEN }}

.gitignore

@@ -1,21 +1,12 @@
 # User-specific files
+.vs/
+.idea/
 *.suo
 *.user
-*.userosscache
-*.sln.docstates
-.idea/
 
 # Build results
-[Dd]ebug/
-[Dd]ebugPublic/
-[Rr]elease/
-[Rr]eleases/
-[Xx]64/
-[Xx]86/
-[Bb]uild/
-bld/
-[Bb]in/
-[Oo]bj/
+bin/
+obj/
 
-# Coverage
-*.opencover.xml
+# Test results
+TestResults/

Changelog.md

@@ -1,19 +1,46 @@
-### v2.2.6 (14-Jun-2022)
+# Changelog
+
+## v2.3.5 (16-Nov-2023)
+
+- Fixed an issue where calling `CliApplication.RunAsync(IReadOnlyList<string>)` could fail in very specific scenarios on Windows, if there were two global environment variables with the same name but different casing. (Thanks [@alirezanet](https://github.com/alirezanet))
+
+## v2.3.4 (18-May-2023)
+
+- Added an overload of `CliApplicationBuilder.UseTypeActivator(...)` that accepts a `Func<IReadOnlyList<Type>, IServiceProvider>` delegate. The first parameter in the delegate is the list of all command types registered in the application. You can use this overload to more easily add the commands to a DI container. See the readme for an [updated example](https://github.com/Tyrrrz/CliFx/tree/2.3.4#type-activation).
+
+## v2.3.3 (28-Apr-2023)
+
+- Fixed an issue where the analyzers failed to load in some projects, due to targeting a Roslyn version that was too high.
+
+## v2.3.2 (06-Apr-2023)
+
+- Added name-based ordering to subcommands when displayed in the help text. (Thanks [@CartBlanche](https://github.com/CartBlanche))
+
+## v2.3.1 (08-Dec-2022)
+
+- Added support for the `required` keyword introduced in C# 11. Command options bound to required properties are now marked as required by default (equivalent to setting `IsRequired = true` on the attribute). Also added analyzers that prevent marking an option or parameter non-required if it's bound to a required property.
+
+## v2.3 (12-Jul-2022)
+
+- Added console dimension properties `WindowWidth` and `WindowHeight` to `IConsole` interface and implementing classes.
+- Improved inline documentation for members of `IConsole` interface.
+
+## v2.2.6 (14-Jun-2022)
 
 - Added an overload of `CliApplicationBuilder.UseTypeActivator(...)` that accepts an instance of `IServiceProvider`. This slightly simplifies integration with many DI containers.
 - Fixed minor grammar mistakes in user-facing error messages.
 
-### v2.2.5 (10-May-2022)
+## v2.2.5 (10-May-2022)
 
 - Updated default value resolution for the application executable name. It will now resolve to `myapp.exe` instead of `dotnet myapp.dll` when the application is launched through the EXE apphost on Windows. On other platforms, or when running the application through the .NET CLI, the behavior will be the same as before.
 
-### v2.2.4 (22-Apr-2022)
+## v2.2.4 (22-Apr-2022)
 
 - Added more contextual information to analyzer diagnostics.
 - Fixed an issue where the analyzer incorrectly reported an error on converters that didn't directly match the target type but were compatible through known built-in conversions.
 - Fixed an issue where MSBuild produced a lot of analyzer-related warnings in certain circumstances.
 
-### v2.2.3 (17-Apr-2022)
+## v2.2.3 (17-Apr-2022)
 
 - Changed method signature of `IConsole.ReadKey()` to return `ConsoleKeyInfo` instead of `void`. The return type was originally defined as `void` by mistake. This change is source-backwards-compatible but may break on binary level if you were previously calling this method indirectly (i.e. through a library).
 - Added `FakeConsole.EnqueueKey(...)` to facilitate the testing of `IConsole.ReadKey()`. You can use this method to simulate key presses in your application.
@@ -21,57 +48,57 @@
 - Improved diagnostics produced by analyzers. Where relevant, highlighted code is now limited to the property or type identifier, instead of the whole property or type declaration. Also extended the diagnostic messages with additional information.
 - Fixed an issue where throwing an exception inside a constructor of a command type resulted in an unrelated error message about the absence of a parameterless constructor.
 
-### v2.2.2 (30-Jan-2022)
+## v2.2.2 (30-Jan-2022)
 
 - Fixed an issue where `ConsoleWriter` and `ConsoleReader` were not properly thread-safe.
 - Fixed an issue where the analyzer failed to load under certain circumstances when running inside Visual Studio.
 
-### v2.2.1 (16-Jan-2022)
+## v2.2.1 (16-Jan-2022)
 
 - Fixed an issue which caused help text to not show default values for optional parameters. (Thanks [@AliReZa Sabouri](https://github.com/alirezanet))
 
-### v2.2 (11-Jan-2022)
+## v2.2 (11-Jan-2022)
 
 - Added support for optional parameters. A parameter can be marked as optional by setting `IsRequired = false` on the attribute. Only one parameter is allowed to be optional and such parameter must be the last in order. (Thanks [@AliReZa Sabouri](https://github.com/alirezanet))
 - Fixed an issue where parameters and options bound to properties implemented as default interface members were not working correctly. (Thanks [@AliReZa Sabouri](https://github.com/alirezanet))
 
-### v2.1 (04-Jan-2022)
+## v2.1 (04-Jan-2022)
 
 - Added `IConsole.Clear()` with corresponding implementations in `SystemConsole`, `FakeConsole`, and `FakeInMemoryConsole`. (Thanks [@Alex Rosenfeld](https://github.com/alexrosenfeld10))
 - Added `IConsole.ReadKey()` with corresponding implementations in `SystemConsole`, `FakeConsole`, and `FakeInMemoryConsole`. (Thanks [@Alex Rosenfeld](https://github.com/alexrosenfeld10))
 - Fixed an issue that caused parameters to appear out of order in the usage format section of the help text. (Thanks [@David Fallah](https://github.com/TAGC))
 
-### v2.0.6 (17-Jul-2021)
+## v2.0.6 (17-Jul-2021)
 
 - Fixed an issue where an exception thrown via reflection during parameter or option binding resulted in `Exception has been thrown by the target of an invocation` error instead of a more useful message. Such exceptions will now be unwrapped to provide better user experience.
 
-### v2.0.5 (09-Jul-2021)
+## v2.0.5 (09-Jul-2021)
 
 - Fixed an issue where calling `IConsole.Output.Encoding.EncodingName` and some other members threw an exception.
 - Added readme file to the package.
 
-### v2.0.4 (24-Apr-2021)
+## v2.0.4 (24-Apr-2021)
 
 - Fixed an issue where output and error streams in `SystemConsole` defaulted to UTF8 encoding with BOM when the application was running with UTF8 codepage. `ConsoleWriter` will now discard preamble from the specified encoding. This fix brings the behavior of `SystemConsole` in line with .NET's own `System.Console` which also discards preamble for output and error streams.
 - Fixed an issue where help text tried to show default values for parameters and options whose type does not override `ToString()` method.
 - Fixed an issue where help text didn't show default values for parameters and options whose type is an enumerable of nullable enums. (Thanks [@Robert Dailey](https://github.com/rcdailey))
 - Fixed an issue where specific parts of the help text weren't legible in some terminals due to low color resolution. Removed the usage of `ConsoleColor.DarkGray` in help text.
 
-### v2.0.3 (09-Apr-2021)
+## v2.0.3 (09-Apr-2021)
 
 - Improved help text by showing valid values for non-scalar enum parameters and options. (Thanks [@Robert Dailey](https://github.com/rcdailey))
 
-### v2.0.2 (31-Mar-2021)
+## v2.0.2 (31-Mar-2021)
 
 - Fixed an issue where having a transitive reference to CliFx sometimes resulted in `SystemConsoleShouldBeAvoidedAnalyzer` throwing `NullReferenceException` during build.
 - Fixed some documentation typos and inconsistencies.
 
-### v2.0.1 (24-Mar-2021)
+## v2.0.1 (24-Mar-2021)
 
 - Fixed an issue where some exceptions with async stack traces generated on .NET 3.1 or earlier were not parsed and formatted correctly.
 - Fixed an issue where help text applied slightly incorrect formatting when displaying choices for enum-based parameters and properties.
 
-### v2.0 (21-Mar-2021)
+## v2.0 (21-Mar-2021)
 
 > Note: this major release includes many breaking changes.
 > Please refer to the readme to find updated instructions and usage examples.
@@ -91,7 +118,7 @@
   - Assigned separate colors to parameters and options to make them visually stand out
   - Usage section no longer lists usage formats of all descendant commands
   - Command section now also lists available subcommands for each of the current command's subcommands
-- Changed the behavior of `[preview]` directive. Running the application with this directive will now also print all resolved environment variables, in addition to parsed command line arguments.
+- Changed the behavior of `[preview]` directive. Running the application with this directive will now also print all resolved environment variables, in addition to parsed command-line arguments.
 - Reworked `IArgumentValueConverter`/`ArgumentValueConverter` into `BindingConverter`. Method `ConvertFrom(...)` has been renamed to `Convert(...)`.
 - Reworked `ArgumentValueValidator` into `BindingValidator`. This class exposes an abstract `Validate(...)` method that returns a nullable `BindingValidationError`. This class also provides utility methods `Ok()` and `Error(...)` to help create corresponding validation results.
 - Changed the type of `IConsole.Output` and `IConsole.Error` from `StreamWriter` to `ConsoleWriter`. This type derives from `StreamWriter` and additionally exposes a `Console` property that refers to the console instance that owns the stream. This change enables you to author extension methods scoped specifically to console output and error streams.
@@ -105,34 +132,34 @@
   - `ITypeActivator`/`DefaultTypeActivator`/`DelegateTypeActivator` moved from `CliFx` to `CliFx.Infrastructure`
   - `BindingValidator`/`BindingConverter` moved from `CliFx` to `CliFx.Extensibility`
 
-### v1.6 (06-Dec-2020)
+## v1.6 (06-Dec-2020)
 
 - Added support for custom value validators. You can now create a type that inherits from `CliFx.ArgumentValueValidator<T>` to implement reusable validation logic for command arguments. To use a validator, include it in the `Validators` property on the `CommandOption` or `CommandParameter` attribute. (Thanks [@Oleksandr Shustov](https://github.com/AlexandrShustov))
 - Added `CliFx.ArgumentValueConverter<T>` class that you can inherit from to implement custom value converters. `CliFx.IArgumentValueConverter` interface is still available, but it is recommended to inherit from the generic class instead, due to the type safety it provides. The interface may become internal or get removed in one of the future major versions.
 - Updated requirements for option names and short names: short names now must be letter characters (lowercase or uppercase), while names must now start with a letter character. This means option names can no longer start with a digit or a special character. This change makes it possible to pass negative number values without the need to quote them, i.e. `--my-number -5`.
 
-### v1.5 (23-Oct-2020)
+## v1.5 (23-Oct-2020)
 
 - Added pretty-printing for unhandled exceptions thrown from within the application. This makes the errors easier to parse visually and should help in troubleshooting. This change does not affect `CommandException`, as it already has special treatment. (Thanks [@Mårten Åsberg](https://github.com/89netraM))
 - Added support for custom value converters. You can now create a type that implements `CliFx.IArgumentValueConverter` and specify it as a converter for your parameters or options via the `Converter` named property. This should enable conversion between raw argument values and custom types which are not string-initializable. (Thanks [@Oleksandr Shustov](https://github.com/AlexandrShustov))
 - Improved help text so that it also shows minimal usage examples for child and descendant commands, besides the actual command it was requested on. This should improve user experience for applications with many nested commands. (Thanks [@Nikiforov Alexey](https://github.com/NikiforovAll))
 
-### v1.4 (20-Aug-2020)
+## v1.4 (20-Aug-2020)
 
 - Added `VirtualConsole.CreateBuffered()` method to simplify test setup when using in-memory backing stores for output and error streams. Please refer to the readme for updated recommendations on how to test applications built with CliFx.
 - Added generic `CliApplicationBuilder.AddCommand<TCommand>()`. This overload simplifies adding commands one-by-one as it also checks that the type implements `ICommand`.
 
-### v1.3.2 (31-Jul-2020)
+## v1.3.2 (31-Jul-2020)
 
 - Fixed an issue where a command was incorrectly allowed to execute when the user did not specify any value for a non-scalar parameter. Since they are always required, a parameter needs to be bound to at least one value. (Thanks [@Daniel Hix](https://github.com/ADustyOldMuffin))
 - Fixed an issue where `CliApplication.RunAsync(...)` threw `ArgumentException` if there were two environment variables, whose names differed only in case. Environment variable names are now treated case-sensitively. (Thanks [@Ron Myers](https://github.com/ron-myers))
 
-### v1.3.1 (19-Jul-2020)
+## v1.3.1 (19-Jul-2020)
 
 - Running the application with the debug directive (`myapp [debug]`) will now also try to launch a debugger instance. In most cases it will save time as you won't need to attach the debugger manually. (Thanks [@Volodymyr Shkolka](https://github.com/BlackGad))
 - Fixed an issue where unhandled generic exceptions (i.e. not `CommandException`) sometimes caused the application to incorrectly return successful exit code due to an overflow issue on Unix systems. Starting from this version, all unhandled generic exceptions will produce `1` as the exit code when thrown. Instances of `CommandException` can still be configured to return any specified exit code, but it's recommended to constrain the values between `1` and `255` to avoid overflow issues. (Thanks [@Ihor Nechyporuk](https://github.com/inech))
 
-### v1.3 (23-May-2020)
+## v1.3 (23-May-2020)
 
 - Changed analyzers to report errors instead of warnings. If you find that some analyzer works incorrectly, please report it on GitHub. You can also configure inspection severity overrides in your project if you need to.
 - Improved help text by showing default values for non-required options. This only works on types that have a custom override for `ToString()` method. Additionally, if the type implements `IFormattable`, the overload with a format provider will be used instead. (Thanks [@Domn Werner](https://github.com/domn1995))
@@ -140,7 +167,7 @@
 - Fixed an issue where it was possible to define a command with an option that has the same name or short name as built-in help or version options. Previously it would lead to the user-defined option being ignored in favor of the built-in option. Now this will throw an exception instead.
 - Changed the underlying representation of `StreamReader`/`StreamWriter` objects used in `SystemConsole` and `VirtualConsole` to be thread-safe.
 
-### v1.2 (11-May-2020)
+## v1.2 (11-May-2020)
 
 - Added built-in Roslyn analyzers that help catch incorrect usage of the library. Currently, all analyzers report issues as warnings so as to not prevent the project from building. In the future that may change.
 - Added an optional parameter to `new CommandException(...)` called `showHelp` which can be used to instruct CliFx to show help for the current command after printing the error. (Thanks [@Domn Werner](https://github.com/domn1995))
@@ -151,7 +178,7 @@
 - Improved exception messages.
 - Improved exceptions related to user input by also showing help text after the error message. (Thanks [@Domn Werner](https://github.com/domn1995))
 
-### v1.1 (16-Mar-2020)
+## v1.1 (16-Mar-2020)
 
 - Changed `IConsole` interface (and as a result, `SystemConsole` and `VirtualConsole`) to support writing binary data. Instead of `TextReader`/`TextWriter` instances, the streams are now exposed as `StreamReader`/`StreamWriter` which provide the `BaseStream` property that allows raw access. Existing usages inside commands should remain the same because `StreamReader`/`StreamWriter` are compatible with their base classes `TextReader`/`TextWriter`, but if you were using `VirtualConsole` in tests, you may have to update it to the new API. Refer to the readme for more info.
 - Changed argument binding behavior so that an error is produced if the user provides an argument that doesn't match with any parameter or option. This is done in order to improve user experience, as otherwise the user may make a typo without knowing that their input wasn't taken into account.

CliFx.Analyzers.Tests/CliFx.Analyzers.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
@@ -9,14 +9,15 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Basic.Reference.Assemblies" Version="1.2.4" />
-    <PackageReference Include="GitHubActionsTestLogger" Version="2.0.0" PrivateAssets="all" />
-    <PackageReference Include="FluentAssertions" Version="6.7.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.2.0" />
-    <PackageReference Include="xunit" Version="2.4.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" PrivateAssets="all" />
-    <PackageReference Include="coverlet.collector" Version="3.1.2" PrivateAssets="all" />
+    <PackageReference Include="Basic.Reference.Assemblies.Net70" Version="1.4.5" />
+    <PackageReference Include="coverlet.collector" Version="6.0.0" PrivateAssets="all" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.26.1" PrivateAssets="all" />
+    <PackageReference Include="GitHubActionsTestLogger" Version="2.3.3" PrivateAssets="all" />
+    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.7.0" />
+    <PackageReference Include="xunit" Version="2.6.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Analyzers.Tests/CommandMustBeAnnotatedAnalyzerSpecs.cs

@@ -12,12 +12,13 @@ public class CommandMustBeAnnotatedAnalyzerSpecs
     public void Analyzer_reports_an_error_if_a_command_is_not_annotated_with_the_command_attribute()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -27,13 +28,14 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_command_is_annotated_with_the_command_attribute()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public abstract class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -43,12 +45,13 @@ public abstract class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_command_is_implemented_as_an_abstract_class()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public abstract class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -58,12 +61,13 @@ public abstract class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_class_that_is_not_a_command()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class Foo
             {
-    public int Bar { get; set; } = 5;
-}";
+                public int Bar { get; init; } = 5;
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/CommandMustImplementInterfaceAnalyzerSpecs.cs

@@ -6,19 +6,21 @@ namespace CliFx.Analyzers.Tests;
 
 public class CommandMustImplementInterfaceAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new CommandMustImplementInterfaceAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new CommandMustImplementInterfaceAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_command_does_not_implement_ICommand_interface()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand
             {
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -28,13 +30,14 @@ public class MyCommand
     public void Analyzer_does_not_report_an_error_if_a_command_implements_ICommand_interface()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -44,12 +47,13 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_class_that_is_not_a_command()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class Foo
             {
-    public int Bar { get; set; } = 5;
-}";
+                public int Bar { get; init; } = 5;
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustBeInsideCommandAnalyzerSpecs.cs

@@ -12,13 +12,14 @@ public class OptionMustBeInsideCommandAnalyzerSpecs
     public void Analyzer_reports_an_error_if_an_option_is_inside_a_class_that_is_not_a_command()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyClass
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
-}";
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -28,16 +29,17 @@ public class MyClass
     public void Analyzer_does_not_report_an_error_if_an_option_is_inside_a_command()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -47,13 +49,14 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_is_inside_an_abstract_class()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public abstract class MyCommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
-}";
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -63,15 +66,16 @@ public abstract class MyCommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustBeRequiredIfPropertyRequiredAnalyzerSpecs.cs

@@ -0,0 +1,110 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests;
+
+public class OptionMustBeRequiredIfPropertyRequiredAnalyzerSpecs
+{
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new OptionMustBeRequiredIfPropertyRequiredAnalyzer();
+
+    [Fact]
+    public void Analyzer_reports_an_error_if_a_non_required_option_is_bound_to_a_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandOption('f', IsRequired = false)]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().ProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_a_required_option_is_bound_to_a_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandOption('f')]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_a_non_required_option_is_bound_to_a_non_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandOption('f', IsRequired = false)]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_a_required_option_is_bound_to_a_non_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandOption('f')]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveNameOrShortNameAnalyzerSpecs.cs

@@ -6,22 +6,24 @@ namespace CliFx.Analyzers.Tests;
 
 public class OptionMustHaveNameOrShortNameAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveNameOrShortNameAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new OptionMustHaveNameOrShortNameAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_an_option_does_not_have_a_name_or_short_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption(null)]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -31,16 +33,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -50,16 +53,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_short_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -69,15 +73,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustHaveUniqueNameAnalyzerSpecs.cs

@@ -12,19 +12,20 @@ public class OptionMustHaveUniqueNameAnalyzerSpecs
     public void Analyzer_reports_an_error_if_an_option_has_the_same_name_as_another_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
-    [CommandOption(""foo"")]
-    public string Bar { get; set; }
+                [CommandOption("foo")]
+                public string? Bar { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +35,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_unique_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
-    [CommandOption(""bar"")]
-    public string Bar { get; set; }
+                [CommandOption("bar")]
+                public string? Bar { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,16 +58,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -75,15 +78,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustHaveUniqueShortNameAnalyzerSpecs.cs

@@ -6,25 +6,27 @@ namespace CliFx.Analyzers.Tests;
 
 public class OptionMustHaveUniqueShortNameAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveUniqueShortNameAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new OptionMustHaveUniqueShortNameAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_an_option_has_the_same_short_name_as_another_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 [CommandOption('f')]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +36,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_unique_short_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 [CommandOption('b')]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,19 +59,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_short_name_which_is_unique_only_in_casing()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 [CommandOption('F')]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -78,16 +82,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_short_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -97,15 +102,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustHaveValidConverterAnalyzerSpecs.cs

@@ -6,27 +6,29 @@ namespace CliFx.Analyzers.Tests;
 
 public class OptionMustHaveValidConverterAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveValidConverterAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new OptionMustHaveValidConverterAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_an_option_has_a_converter_that_does_not_derive_from_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter
             {
-    public string Convert(string rawValue) => rawValue;
+                public string Convert(string? rawValue) => rawValue;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Converter = typeof(MyConverter))]
-    public string Foo { get; set; }
+                [CommandOption("foo", Converter = typeof(MyConverter))]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -36,21 +38,22 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_an_option_has_a_converter_that_does_not_derive_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<int>
             {
-    public override int Convert(string rawValue) => 42;
+                public override int Convert(string? rawValue) => 42;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Converter = typeof(MyConverter))]
-    public string Foo { get; set; }
+                [CommandOption("foo", Converter = typeof(MyConverter))]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -60,21 +63,22 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_converter_that_derives_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<string>
             {
-    public override string Convert(string rawValue) => rawValue;
+                public override string Convert(string? rawValue) => rawValue;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Converter = typeof(MyConverter))]
-    public string Foo { get; set; }
+                [CommandOption("foo", Converter = typeof(MyConverter))]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -84,21 +88,22 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_nullable_option_has_a_converter_that_derives_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<int>
             {
-    public override int Convert(string rawValue) => 42;
+                public override int Convert(string? rawValue) => 42;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Converter = typeof(MyConverter))]
-    public int? Foo { get; set; }
+                [CommandOption("foo", Converter = typeof(MyConverter))]
+                public int? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -108,21 +113,22 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_non_scalar_option_has_a_converter_that_derives_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<string>
             {
-    public override string Convert(string rawValue) => rawValue;
+                public override string Convert(string? rawValue) => rawValue;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Converter = typeof(MyConverter))]
-    public IReadOnlyList<string> Foo { get; set; }
+                [CommandOption("foo", Converter = typeof(MyConverter))]
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -132,16 +138,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_converter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -151,15 +158,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustHaveValidNameAnalyzerSpecs.cs

@@ -12,16 +12,17 @@ public class OptionMustHaveValidNameAnalyzerSpecs
     public void Analyzer_reports_an_error_if_an_option_has_a_name_which_is_too_short()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""f"")]
-    public string Foo { get; set; }
+                [CommandOption("f")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -31,16 +32,17 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_an_option_has_a_name_that_starts_with_a_non_letter_character()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""1foo"")]
-    public string Foo { get; set; }
+                [CommandOption("1foo")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -50,16 +52,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_valid_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -69,16 +72,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -88,15 +92,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustHaveValidShortNameAnalyzerSpecs.cs

@@ -6,22 +6,24 @@ namespace CliFx.Analyzers.Tests;
 
 public class OptionMustHaveValidShortNameAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveValidShortNameAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new OptionMustHaveValidShortNameAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_an_option_has_a_short_name_which_is_not_a_letter_character()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('1')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -31,16 +33,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_a_valid_short_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -50,16 +53,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_short_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -69,15 +73,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/OptionMustHaveValidValidatorsAnalyzerSpecs.cs

@@ -6,14 +6,15 @@ namespace CliFx.Analyzers.Tests;
 
 public class OptionMustHaveValidValidatorsAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveValidValidatorsAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new OptionMustHaveValidValidatorsAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_an_option_has_a_validator_that_does_not_derive_from_BindingValidator()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyValidator
             {
                 public void Validate(string value) {}
@@ -22,11 +23,12 @@ public class MyValidator
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Validators = new[] {typeof(MyValidator)})]
-    public string Foo { get; set; }
+                [CommandOption("foo", Validators = new[] {typeof(MyValidator)})]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -36,8 +38,8 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_an_option_has_a_validator_that_does_not_derive_from_a_compatible_BindingValidator()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyValidator : BindingValidator<int>
             {
                 public override BindingValidationError Validate(int value) => Ok();
@@ -46,11 +48,12 @@ public class MyValidator : BindingValidator<int>
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Validators = new[] {typeof(MyValidator)})]
-    public string Foo { get; set; }
+                [CommandOption("foo", Validators = new[] {typeof(MyValidator)})]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -60,8 +63,8 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_has_validators_that_all_derive_from_compatible_BindingValidators()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyValidator : BindingValidator<string>
             {
                 public override BindingValidationError Validate(string value) => Ok();
@@ -70,11 +73,12 @@ public class MyValidator : BindingValidator<string>
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Validators = new[] {typeof(MyValidator)})]
-    public string Foo { get; set; }
+                [CommandOption("foo", Validators = new[] {typeof(MyValidator)})]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -84,16 +88,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_validators()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -103,15 +108,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustBeInsideCommandAnalyzerSpecs.cs

@@ -6,19 +6,21 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustBeInsideCommandAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeInsideCommandAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustBeInsideCommandAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_parameter_is_inside_a_class_that_is_not_a_command()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyClass
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
-}";
+                public required string Foo { get; init; }
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -28,16 +30,17 @@ public class MyClass
     public void Analyzer_does_not_report_an_error_if_a_parameter_is_inside_a_command()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -47,13 +50,14 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_is_inside_an_abstract_class()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public abstract class MyCommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
-}";
+                public required string Foo { get; init; }
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -63,15 +67,16 @@ public abstract class MyCommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustBeLastIfNonRequiredAnalyzerSpecs.cs

@@ -6,25 +6,27 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustBeLastIfNonRequiredAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeLastIfNonRequiredAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustBeLastIfNonRequiredAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_non_required_parameter_is_not_the_last_in_order()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandParameter(0, Name = ""foo"", IsRequired = false)]
-    public string Foo { get; set; }
+                [CommandParameter(0, IsRequired = false)]
+                public string? Foo { get; init; }
 
-    [CommandParameter(1, Name = ""bar"")]
-    public string Bar { get; set; }
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +36,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_non_required_parameter_is_the_last_in_order()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandParameter(0, Name = ""foo"")]
-    public string Foo { get; set; }
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
 
-    [CommandParameter(1, Name = ""bar"", IsRequired = false)]
-    public string Bar { get; set; }
+                [CommandParameter(1, IsRequired = false)]
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,19 +59,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_no_non_required_parameters_are_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandParameter(0, Name = ""foo"")]
-    public string Foo { get; set; }
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
 
-    [CommandParameter(1, Name = ""bar"", IsRequired = true)]
-    public string Bar { get; set; }
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -78,15 +82,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustBeLastIfNonScalarAnalyzerSpecs.cs

@@ -6,25 +6,27 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustBeLastIfNonScalarAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeLastIfNonScalarAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustBeLastIfNonScalarAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_non_scalar_parameter_is_not_the_last_in_order()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string[] Foo { get; set; }
+                public required string[] Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +36,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_non_scalar_parameter_is_the_last_in_order()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string[] Bar { get; set; }
+                public required string[] Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,19 +59,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_no_non_scalar_parameters_are_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -78,15 +82,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustBeRequiredIfPropertyRequiredAnalyzerSpecs.cs

@@ -0,0 +1,110 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests;
+
+public class ParameterMustBeRequiredIfPropertyRequiredAnalyzerSpecs
+{
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustBeRequiredIfPropertyRequiredAnalyzer();
+
+    [Fact]
+    public void Analyzer_reports_an_error_if_a_non_required_parameter_is_bound_to_a_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandParameter(0, IsRequired = false)]
+                public required string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().ProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_a_required_parameter_is_bound_to_a_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_a_non_required_parameter_is_bound_to_a_non_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandParameter(0, IsRequired = false)]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_a_required_parameter_is_bound_to_a_non_required_property()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
+    {
+        // Arrange
+        // lang=csharp
+        const string code = """
+            [Command]
+            public class MyCommand : ICommand
+            {
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """;
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+}

CliFx.Analyzers.Tests/ParameterMustBeSingleIfNonRequiredAnalyzerSpecs.cs

@@ -6,25 +6,27 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustBeSingleIfNonRequiredAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeSingleIfNonRequiredAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustBeSingleIfNonRequiredAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_more_than_one_non_required_parameters_are_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, IsRequired = false)]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 [CommandParameter(1, IsRequired = false)]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +36,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_only_one_non_required_parameter_is_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1, IsRequired = false)]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,19 +59,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_no_non_required_parameters_are_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
-    [CommandParameter(1, IsRequired = true)]
-    public string Bar { get; set; }
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -78,15 +82,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustBeSingleIfNonScalarAnalyzerSpecs.cs

@@ -6,25 +6,27 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustBeSingleIfNonScalarAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeSingleIfNonScalarAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustBeSingleIfNonScalarAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_more_than_one_non_scalar_parameters_are_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string[] Foo { get; set; }
+                public required string[] Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string[] Bar { get; set; }
+                public required string[] Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +36,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_only_one_non_scalar_parameter_is_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string[] Bar { get; set; }
+                public required string[] Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,19 +59,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_no_non_scalar_parameters_are_defined()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -78,15 +82,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustHaveUniqueNameAnalyzerSpecs.cs

@@ -12,19 +12,20 @@ public class ParameterMustHaveUniqueNameAnalyzerSpecs
     public void Analyzer_reports_an_error_if_a_parameter_has_the_same_name_as_another_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandParameter(0, Name = ""foo"")]
-    public string Foo { get; set; }
+                [CommandParameter(0, Name = "foo")]
+                public required string Foo { get; init; }
 
-    [CommandParameter(1, Name = ""foo"")]
-    public string Bar { get; set; }
+                [CommandParameter(1, Name = "foo")]
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +35,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_has_unique_name()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandParameter(0, Name = ""foo"")]
-    public string Foo { get; set; }
+                [CommandParameter(0, Name = "foo")]
+                public required string Foo { get; init; }
 
-    [CommandParameter(1, Name = ""bar"")]
-    public string Bar { get; set; }
+                [CommandParameter(1, Name = "bar")]
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,15 +58,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustHaveUniqueOrderAnalyzerSpecs.cs

@@ -6,25 +6,27 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustHaveUniqueOrderAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustHaveUniqueOrderAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustHaveUniqueOrderAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_parameter_has_the_same_order_as_another_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(0)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -34,19 +36,20 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_has_unique_order()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -56,15 +59,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustHaveValidConverterAnalyzerSpecs.cs

@@ -6,27 +6,29 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustHaveValidConverterAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustHaveValidConverterAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustHaveValidConverterAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_parameter_has_a_converter_that_does_not_derive_from_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter
             {
-    public string Convert(string rawValue) => rawValue;
+                public string Convert(string? rawValue) => rawValue;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Converter = typeof(MyConverter))]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -36,22 +38,22 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_a_parameter_has_a_converter_that_does_not_derive_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<int>
             {
-    public override int Convert(string rawValue) => 42;
+                public override int Convert(string? rawValue) => 42;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Converter = typeof(MyConverter))]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
-
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -61,21 +63,22 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_has_a_converter_that_derives_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<string>
             {
-    public override string Convert(string rawValue) => rawValue;
+                public override string Convert(string? rawValue) => rawValue;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Converter = typeof(MyConverter))]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -85,21 +88,22 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_nullable_parameter_has_a_converter_that_derives_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<int>
             {
-    public override int Convert(string rawValue) => 42;
+                public override int Convert(string? rawValue) => 42;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
-    [CommandOption(""foo"", Converter = typeof(MyConverter))]
-    public int? Foo { get; set; }
+                [CommandOption("foo", Converter = typeof(MyConverter))]
+                public int? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -109,21 +113,22 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_non_scalar_parameter_has_a_converter_that_derives_from_a_compatible_BindingConverter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyConverter : BindingConverter<string>
             {
-    public override string Convert(string rawValue) => rawValue;
+                public override string Convert(string? rawValue) => rawValue;
             }
 
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Converter = typeof(MyConverter))]
-    public IReadOnlyList<string> Foo { get; set; }
+                public required IReadOnlyList<string> Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -133,16 +138,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_does_not_have_a_converter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -152,15 +158,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/ParameterMustHaveValidValidatorsAnalyzerSpecs.cs

@@ -6,14 +6,15 @@ namespace CliFx.Analyzers.Tests;
 
 public class ParameterMustHaveValidValidatorsAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustHaveValidValidatorsAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new ParameterMustHaveValidValidatorsAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_a_parameter_has_a_validator_that_does_not_derive_from_BindingValidator()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyValidator
             {
                 public void Validate(string value) {}
@@ -23,10 +24,11 @@ public class MyValidator
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Validators = new[] {typeof(MyValidator)})]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -36,8 +38,8 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_a_parameter_has_a_validator_that_does_not_derive_from_a_compatible_BindingValidator()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyValidator : BindingValidator<int>
             {
                 public override BindingValidationError Validate(int value) => Ok();
@@ -47,10 +49,11 @@ public class MyValidator : BindingValidator<int>
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Validators = new[] {typeof(MyValidator)})]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -60,8 +63,8 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_has_validators_that_all_derive_from_compatible_BindingValidators()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             public class MyValidator : BindingValidator<string>
             {
                 public override BindingValidationError Validate(string value) => Ok();
@@ -71,10 +74,11 @@ public class MyValidator : BindingValidator<string>
             public class MyCommand : ICommand
             {
                 [CommandParameter(0, Validators = new[] {typeof(MyValidator)})]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -84,16 +88,17 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_parameter_does_not_have_validators()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -103,15 +108,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/SystemConsoleShouldBeAvoidedAnalyzerSpecs.cs

@@ -6,23 +6,25 @@ namespace CliFx.Analyzers.Tests;
 
 public class SystemConsoleShouldBeAvoidedAnalyzerSpecs
 {
-    private static DiagnosticAnalyzer Analyzer { get; } = new SystemConsoleShouldBeAvoidedAnalyzer();
+    private static DiagnosticAnalyzer Analyzer { get; } =
+        new SystemConsoleShouldBeAvoidedAnalyzer();
 
     [Fact]
     public void Analyzer_reports_an_error_if_a_command_calls_a_method_on_SystemConsole()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        Console.WriteLine(""Hello world"");
+                    Console.WriteLine("Hello world");
                     return default;
                 }
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -32,8 +34,8 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_a_command_accesses_a_property_on_SystemConsole()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
@@ -42,7 +44,9 @@ public class MyCommand : ICommand
                     Console.ForegroundColor = ConsoleColor.Black;
                     return default;
                 }
-}";
+            }
+            """;
+
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
     }
@@ -51,17 +55,18 @@ public class MyCommand : ICommand
     public void Analyzer_reports_an_error_if_a_command_calls_a_method_on_a_property_of_SystemConsole()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        Console.Error.WriteLine(""Hello world"");
+                    Console.Error.WriteLine("Hello world");
                     return default;
                 }
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().ProduceDiagnostics(code);
@@ -71,17 +76,18 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_command_interacts_with_the_console_through_IConsole()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Hello world"");
+                    console.Output.WriteLine("Hello world");
                     return default;
                 }
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -91,15 +97,16 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_IConsole_is_not_available_in_the_current_method()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
-    public void SomeOtherMethod() => Console.WriteLine(""Test"");
+                public void SomeOtherMethod() => Console.WriteLine("Test");
             
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);
@@ -109,8 +116,8 @@ public class MyCommand : ICommand
     public void Analyzer_does_not_report_an_error_if_a_command_does_not_access_SystemConsole()
     {
         // Arrange
-        // language=cs
-        const string code = @"
+        // lang=csharp
+        const string code = """
             [Command]
             public class MyCommand : ICommand
             {
@@ -118,7 +125,8 @@ public class MyCommand : ICommand
                 {
                     return default;
                 }
-}";
+            }
+            """;
 
         // Act & assert
         Analyzer.Should().NotProduceDiagnostics(code);

CliFx.Analyzers.Tests/Utils/AnalyzerAssertions.cs

@@ -18,9 +18,7 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
     protected override string Identifier { get; } = "analyzer";
 
     public AnalyzerAssertions(DiagnosticAnalyzer analyzer)
-        : base(analyzer)
-    {
-    }
+        : base(analyzer) { }
 
     private Compilation Compile(string sourceCode)
     {
@@ -43,10 +41,10 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
 
         // Append default imports to the source code
         var sourceCodeWithUsings =
-            string.Join(Environment.NewLine, defaultSystemNamespaces.Select(n => $"using {n};")) +
-            string.Join(Environment.NewLine, defaultCliFxNamespaces.Select(n => $"using {n};")) +
-            Environment.NewLine +
-            sourceCode;
+            string.Join(Environment.NewLine, defaultSystemNamespaces.Select(n => $"using {n};"))
+            + string.Join(Environment.NewLine, defaultCliFxNamespaces.Select(n => $"using {n};"))
+            + Environment.NewLine
+            + sourceCode;
 
         // Parse the source code
         var ast = SyntaxFactory.ParseSyntaxTree(
@@ -58,7 +56,9 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
         var compilation = CSharpCompilation.Create(
             "CliFxTests_DynamicAssembly_" + Guid.NewGuid(),
             new[] { ast },
-            ReferenceAssemblies.Net50
+            Net70
+                .References
+                .All
                 .Append(MetadataReference.CreateFromFile(typeof(ICommand).Assembly.Location)),
             // DLL to avoid having to define the Main() method
             new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
@@ -72,9 +72,10 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
         if (compilationErrors.Any())
         {
             throw new InvalidOperationException(
-                "Failed to compile code." +
-                Environment.NewLine +
-                string.Join(Environment.NewLine, compilationErrors.Select(e => e.ToString()))
+                $"""
+                Failed to compile code.
+                {string.Join(Environment.NewLine, compilationErrors.Select(e => e.ToString()))}
+                """
             );
         }
 
@@ -102,10 +103,13 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
         var producedDiagnosticIds = producedDiagnostics.Select(d => d.Id).Distinct().ToArray();
 
         var isSuccessfulAssertion =
-            expectedDiagnosticIds.Intersect(producedDiagnosticIds).Count() ==
-            expectedDiagnosticIds.Length;
+            expectedDiagnosticIds.Intersect(producedDiagnosticIds).Count()
+            == expectedDiagnosticIds.Length;
 
-        Execute.Assertion.ForCondition(isSuccessfulAssertion).FailWith(() =>
+        Execute
+            .Assertion
+            .ForCondition(isSuccessfulAssertion)
+            .FailWith(() =>
             {
                 var buffer = new StringBuilder();
 
@@ -147,7 +151,10 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
         var producedDiagnostics = GetProducedDiagnostics(sourceCode);
         var isSuccessfulAssertion = !producedDiagnostics.Any();
 
-        Execute.Assertion.ForCondition(isSuccessfulAssertion).FailWith(() =>
+        Execute
+            .Assertion
+            .ForCondition(isSuccessfulAssertion)
+            .FailWith(() =>
             {
                 var buffer = new StringBuilder();
 

CliFx.Analyzers/AnalyzerBase.cs

@@ -14,7 +14,8 @@ public abstract class AnalyzerBase : DiagnosticAnalyzer
     protected AnalyzerBase(
         string diagnosticTitle,
         string diagnosticMessage,
-        DiagnosticSeverity diagnosticSeverity = DiagnosticSeverity.Error)
+        DiagnosticSeverity diagnosticSeverity = DiagnosticSeverity.Error
+    )
     {
         SupportedDiagnostic = new DiagnosticDescriptor(
             "CliFx_" + GetType().Name.TrimEnd("Analyzer"),

CliFx.Analyzers/CliFx.Analyzers.csproj

@@ -3,14 +3,25 @@
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
-    <Nullable>annotations</Nullable>
+    <GenerateDependencyFile>true</GenerateDependencyFile>
+    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
     <NoWarn>$(NoWarn);RS1025;RS1026</NoWarn>
   </PropertyGroup>
 
+  <PropertyGroup>
+    <!--
+      Because this project only has a single target framework, the condition in
+      Directory.Build.props does not appear to work. This is a workaround for that.
+    -->
+    <Nullable>annotations</Nullable>
+  </PropertyGroup>
+
   <ItemGroup>
-    <!-- Keep this dependency as low as possible since we can't bundle it -->
-    <!-- https://github.com/Tyrrrz/CliFx/issues/127 -->
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.8.0" PrivateAssets="all" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.26.1" PrivateAssets="all" />
+    <!-- Make sure to target the lowest possible version of the compiler for wider support -->
+    <PackageReference Include="Microsoft.CodeAnalysis" Version="3.0.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.0.0" PrivateAssets="all" />
+    <PackageReference Include="PolyShim" Version="1.8.0" PrivateAssets="all" />
   </ItemGroup>
 
 </Project>

CliFx.Analyzers/CommandMustBeAnnotatedAnalyzer.cs

@@ -13,14 +13,14 @@ public class CommandMustBeAnnotatedAnalyzer : AnalyzerBase
     public CommandMustBeAnnotatedAnalyzer()
         : base(
             $"Commands must be annotated with `{SymbolNames.CliFxCommandAttribute}`",
-            $"This type must be annotated with `{SymbolNames.CliFxCommandAttribute}` in order to be a valid command.")
-    {
-    }
+            $"This type must be annotated with `{SymbolNames.CliFxCommandAttribute}` in order to be a valid command."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         ClassDeclarationSyntax classDeclaration,
-        ITypeSymbol type)
+        ITypeSymbol type
+    )
     {
         // Ignore abstract classes, because they may be used to define
         // base implementations for commands, in which case the command
@@ -28,12 +28,11 @@ public class CommandMustBeAnnotatedAnalyzer : AnalyzerBase
         if (type.IsAbstract)
             return;
 
-        var implementsCommandInterface = type
-            .AllInterfaces
-            .Any(i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+        var implementsCommandInterface = type.AllInterfaces.Any(
+            i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface)
+        );
 
-        var hasCommandAttribute = type
-            .GetAttributes()
+        var hasCommandAttribute = type.GetAttributes()
             .Select(a => a.AttributeClass)
             .Any(c => c.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
 
@@ -41,9 +40,7 @@ public class CommandMustBeAnnotatedAnalyzer : AnalyzerBase
         // then it's very likely a user error.
         if (implementsCommandInterface && !hasCommandAttribute)
         {
-            context.ReportDiagnostic(
-                CreateDiagnostic(classDeclaration.Identifier.GetLocation())
-            );
+            context.ReportDiagnostic(CreateDiagnostic(classDeclaration.Identifier.GetLocation()));
         }
     }
 

CliFx.Analyzers/CommandMustImplementInterfaceAnalyzer.cs

@@ -13,31 +13,28 @@ public class CommandMustImplementInterfaceAnalyzer : AnalyzerBase
     public CommandMustImplementInterfaceAnalyzer()
         : base(
             $"Commands must implement `{SymbolNames.CliFxCommandInterface}` interface",
-            $"This type must implement `{SymbolNames.CliFxCommandInterface}` interface in order to be a valid command.")
-    {
-    }
+            $"This type must implement `{SymbolNames.CliFxCommandInterface}` interface in order to be a valid command."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         ClassDeclarationSyntax classDeclaration,
-        ITypeSymbol type)
+        ITypeSymbol type
+    )
     {
-        var hasCommandAttribute = type
-            .GetAttributes()
+        var hasCommandAttribute = type.GetAttributes()
             .Select(a => a.AttributeClass)
             .Any(c => c.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
 
-        var implementsCommandInterface = type
-            .AllInterfaces
-            .Any(i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+        var implementsCommandInterface = type.AllInterfaces.Any(
+            i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface)
+        );
 
         // If the attribute is present, but the interface is not implemented,
         // it's very likely a user error.
         if (hasCommandAttribute && !implementsCommandInterface)
         {
-            context.ReportDiagnostic(
-                CreateDiagnostic(classDeclaration.Identifier.GetLocation())
-            );
+            context.ReportDiagnostic(CreateDiagnostic(classDeclaration.Identifier.GetLocation()));
         }
     }
 

CliFx.Analyzers/ObjectModel/CommandOptionSymbol.cs

@@ -13,6 +13,8 @@ internal partial class CommandOptionSymbol : ICommandMemberSymbol
 
     public char? ShortName { get; }
 
+    public bool? IsRequired { get; }
+
     public ITypeSymbol? ConverterType { get; }
 
     public IReadOnlyList<ITypeSymbol> ValidatorTypes { get; }
@@ -21,12 +23,15 @@ internal partial class CommandOptionSymbol : ICommandMemberSymbol
         IPropertySymbol property,
         string? name,
         char? shortName,
+        bool? isRequired,
         ITypeSymbol? converterType,
-        IReadOnlyList<ITypeSymbol> validatorTypes)
+        IReadOnlyList<ITypeSymbol> validatorTypes
+    )
     {
         Property = property;
         Name = name;
         ShortName = shortName;
+        IsRequired = isRequired;
         ConverterType = converterType;
         ValidatorTypes = validatorTypes;
     }
@@ -34,9 +39,14 @@ internal partial class CommandOptionSymbol : ICommandMemberSymbol
 
 internal partial class CommandOptionSymbol
 {
-    private static AttributeData? TryGetOptionAttribute(IPropertySymbol property) => property
+    private static AttributeData? TryGetOptionAttribute(IPropertySymbol property) =>
+        property
             .GetAttributes()
-        .FirstOrDefault(a => a.AttributeClass?.DisplayNameMatches(SymbolNames.CliFxCommandOptionAttribute) == true);
+            .FirstOrDefault(
+                a =>
+                    a.AttributeClass?.DisplayNameMatches(SymbolNames.CliFxCommandOptionAttribute)
+                    == true
+            );
 
     public static CommandOptionSymbol? TryResolve(IPropertySymbol property)
     {
@@ -44,18 +54,27 @@ internal partial class CommandOptionSymbol
         if (attribute is null)
             return null;
 
-        var name = attribute
+        var name =
+            attribute
                 .ConstructorArguments
                 .Where(a => a.Type?.SpecialType == SpecialType.System_String)
                 .Select(a => a.Value)
                 .FirstOrDefault() as string;
 
-        var shortName = attribute
+        var shortName =
+            attribute
                 .ConstructorArguments
                 .Where(a => a.Type?.SpecialType == SpecialType.System_Char)
                 .Select(a => a.Value)
                 .FirstOrDefault() as char?;
 
+        var isRequired =
+            attribute
+                .NamedArguments
+                .Where(a => a.Key == "IsRequired")
+                .Select(a => a.Value.Value)
+                .FirstOrDefault() as bool?;
+
         var converter = attribute
             .NamedArguments
             .Where(a => a.Key == "Converter")
@@ -71,7 +90,14 @@ internal partial class CommandOptionSymbol
             .Cast<ITypeSymbol>()
             .ToArray();
 
-        return new CommandOptionSymbol(property, name, shortName, converter, validators);
+        return new CommandOptionSymbol(
+            property,
+            name,
+            shortName,
+            isRequired,
+            converter,
+            validators
+        );
     }
 
     public static bool IsOptionProperty(IPropertySymbol property) =>

CliFx.Analyzers/ObjectModel/CommandParameterSymbol.cs

@@ -25,7 +25,8 @@ internal partial class CommandParameterSymbol : ICommandMemberSymbol
         string? name,
         bool? isRequired,
         ITypeSymbol? converterType,
-        IReadOnlyList<ITypeSymbol> validatorTypes)
+        IReadOnlyList<ITypeSymbol> validatorTypes
+    )
     {
         Property = property;
         Order = order;
@@ -38,9 +39,14 @@ internal partial class CommandParameterSymbol : ICommandMemberSymbol
 
 internal partial class CommandParameterSymbol
 {
-    private static AttributeData? TryGetParameterAttribute(IPropertySymbol property) => property
+    private static AttributeData? TryGetParameterAttribute(IPropertySymbol property) =>
+        property
             .GetAttributes()
-        .FirstOrDefault(a => a.AttributeClass?.DisplayNameMatches(SymbolNames.CliFxCommandParameterAttribute) == true);
+            .FirstOrDefault(
+                a =>
+                    a.AttributeClass?.DisplayNameMatches(SymbolNames.CliFxCommandParameterAttribute)
+                    == true
+            );
 
     public static CommandParameterSymbol? TryResolve(IPropertySymbol property)
     {
@@ -48,18 +54,17 @@ internal partial class CommandParameterSymbol
         if (attribute is null)
             return null;
 
-        var order = (int)attribute
-            .ConstructorArguments
-            .Select(a => a.Value)
-            .First()!;
+        var order = (int)attribute.ConstructorArguments.Select(a => a.Value).First()!;
 
-        var name = attribute
+        var name =
+            attribute
                 .NamedArguments
                 .Where(a => a.Key == "Name")
                 .Select(a => a.Value.Value)
                 .FirstOrDefault() as string;
 
-        var isRequired = attribute
+        var isRequired =
+            attribute
                 .NamedArguments
                 .Where(a => a.Key == "IsRequired")
                 .Select(a => a.Value.Value)

CliFx.Analyzers/ObjectModel/ICommandMemberSymbol.cs

@@ -16,6 +16,6 @@ internal interface ICommandMemberSymbol
 internal static class CommandMemberSymbolExtensions
 {
     public static bool IsScalar(this ICommandMemberSymbol member) =>
-        member.Property.Type.SpecialType == SpecialType.System_String ||
-        member.Property.Type.TryGetEnumerableUnderlyingType() is null;
+        member.Property.Type.SpecialType == SpecialType.System_String
+        || member.Property.Type.TryGetEnumerableUnderlyingType() is null;
 }

CliFx.Analyzers/ObjectModel/SymbolNames.cs

@@ -4,7 +4,8 @@ internal static class SymbolNames
 {
     public const string CliFxCommandInterface = "CliFx.ICommand";
     public const string CliFxCommandAttribute = "CliFx.Attributes.CommandAttribute";
-    public const string CliFxCommandParameterAttribute = "CliFx.Attributes.CommandParameterAttribute";
+    public const string CliFxCommandParameterAttribute =
+        "CliFx.Attributes.CommandParameterAttribute";
     public const string CliFxCommandOptionAttribute = "CliFx.Attributes.CommandOptionAttribute";
     public const string CliFxConsoleInterface = "CliFx.Infrastructure.IConsole";
     public const string CliFxBindingConverterClass = "CliFx.Extensibility.BindingConverter<T>";

CliFx.Analyzers/OptionMustBeInsideCommandAnalyzer.cs

@@ -13,14 +13,14 @@ public class OptionMustBeInsideCommandAnalyzer : AnalyzerBase
     public OptionMustBeInsideCommandAnalyzer()
         : base(
             "Options must be defined inside commands",
-            $"This option must be defined inside a class that implements `{SymbolNames.CliFxCommandInterface}`.")
-    {
-    }
+            $"This option must be defined inside a class that implements `{SymbolNames.CliFxCommandInterface}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;

CliFx.Analyzers/OptionMustBeRequiredIfPropertyRequiredAnalyzer.cs

@@ -0,0 +1,45 @@
+using CliFx.Analyzers.ObjectModel;
+using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CliFx.Analyzers;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class OptionMustBeRequiredIfPropertyRequiredAnalyzer : AnalyzerBase
+{
+    public OptionMustBeRequiredIfPropertyRequiredAnalyzer()
+        : base(
+            "Options bound to required properties cannot be marked as non-required",
+            "This option cannot be marked as non-required because it's bound to a required property."
+        ) { }
+
+    private void Analyze(
+        SyntaxNodeAnalysisContext context,
+        PropertyDeclarationSyntax propertyDeclaration,
+        IPropertySymbol property
+    )
+    {
+        if (property.ContainingType is null)
+            return;
+
+        if (!property.IsRequired())
+            return;
+
+        var option = CommandOptionSymbol.TryResolve(property);
+        if (option is null)
+            return;
+
+        if (option.IsRequired != false)
+            return;
+
+        context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.Identifier.GetLocation()));
+    }
+
+    public override void Initialize(AnalysisContext context)
+    {
+        base.Initialize(context);
+        context.HandlePropertyDeclaration(Analyze);
+    }
+}

CliFx.Analyzers/OptionMustHaveNameOrShortNameAnalyzer.cs

@@ -12,14 +12,14 @@ public class OptionMustHaveNameOrShortNameAnalyzer : AnalyzerBase
     public OptionMustHaveNameOrShortNameAnalyzer()
         : base(
             "Options must have either a name or short name specified",
-            "This option must have either a name or short name specified.")
-    {
-    }
+            "This option must have either a name or short name specified."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var option = CommandOptionSymbol.TryResolve(property);
         if (option is null)

CliFx.Analyzers/OptionMustHaveUniqueNameAnalyzer.cs

@@ -14,16 +14,16 @@ public class OptionMustHaveUniqueNameAnalyzer : AnalyzerBase
     public OptionMustHaveUniqueNameAnalyzer()
         : base(
             "Options must have unique names",
-            "This option's name must be unique within the command (comparison IS NOT case sensitive). " +
-            "Specified name: `{0}`. " +
-            "Property bound to another option with the same name: `{1}`.")
-    {
-    }
+            "This option's name must be unique within the command (comparison IS NOT case sensitive). "
+                + "Specified name: `{0}`. "
+                + "Property bound to another option with the same name: `{1}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -39,7 +39,7 @@ public class OptionMustHaveUniqueNameAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/OptionMustHaveUniqueShortNameAnalyzer.cs

@@ -13,16 +13,16 @@ public class OptionMustHaveUniqueShortNameAnalyzer : AnalyzerBase
     public OptionMustHaveUniqueShortNameAnalyzer()
         : base(
             "Options must have unique short names",
-            "This option's short name must be unique within the command (comparison IS case sensitive). " +
-            "Specified short name: `{0}` " +
-            "Property bound to another option with the same short name: `{1}`.")
-    {
-    }
+            "This option's short name must be unique within the command (comparison IS case sensitive). "
+                + "Specified short name: `{0}` "
+                + "Property bound to another option with the same short name: `{1}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -38,7 +38,7 @@ public class OptionMustHaveUniqueShortNameAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/OptionMustHaveValidConverterAnalyzer.cs

@@ -13,14 +13,14 @@ public class OptionMustHaveValidConverterAnalyzer : AnalyzerBase
     public OptionMustHaveValidConverterAnalyzer()
         : base(
             $"Option converters must derive from `{SymbolNames.CliFxBindingConverterClass}`",
-            $"Converter specified for this option must derive from a compatible `{SymbolNames.CliFxBindingConverterClass}`.")
-    {
-    }
+            $"Converter specified for this option must derive from a compatible `{SymbolNames.CliFxBindingConverterClass}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var option = CommandOptionSymbol.TryResolve(property);
         if (option is null)
@@ -32,18 +32,24 @@ public class OptionMustHaveValidConverterAnalyzer : AnalyzerBase
         var converterValueType = option
             .ConverterType
             .GetBaseTypes()
-            .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingConverterClass))?
-            .TypeArguments
+            .FirstOrDefault(
+                t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingConverterClass)
+            )
+            ?.TypeArguments
             .FirstOrDefault();
 
         // Value returned by the converter must be assignable to the property type
         var isCompatible =
-            converterValueType is not null && (option.IsScalar()
+            converterValueType is not null
+            && (
+                option.IsScalar()
                     // Scalar
                     ? context.Compilation.IsAssignable(converterValueType, property.Type)
                     // Non-scalar (assume we can handle all IEnumerable types for simplicity)
-                : property.Type.TryGetEnumerableUnderlyingType() is { } enumerableUnderlyingType &&
-                  context.Compilation.IsAssignable(converterValueType, enumerableUnderlyingType)
+                    : property.Type.TryGetEnumerableUnderlyingType() is { } enumerableUnderlyingType
+                        && context
+                            .Compilation
+                            .IsAssignable(converterValueType, enumerableUnderlyingType)
             );
 
         if (!isCompatible)

CliFx.Analyzers/OptionMustHaveValidNameAnalyzer.cs

@@ -12,15 +12,15 @@ public class OptionMustHaveValidNameAnalyzer : AnalyzerBase
     public OptionMustHaveValidNameAnalyzer()
         : base(
             "Options must have valid names",
-            "This option's name must be at least 2 characters long and must start with a letter. " +
-            "Specified name: `{0}`.")
-    {
-    }
+            "This option's name must be at least 2 characters long and must start with a letter. "
+                + "Specified name: `{0}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var option = CommandOptionSymbol.TryResolve(property);
         if (option is null)
@@ -32,10 +32,7 @@ public class OptionMustHaveValidNameAnalyzer : AnalyzerBase
         if (option.Name.Length < 2 || !char.IsLetter(option.Name[0]))
         {
             context.ReportDiagnostic(
-                CreateDiagnostic(
-                    propertyDeclaration.Identifier.GetLocation(),
-                    option.Name
-                )
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation(), option.Name)
             );
         }
     }

CliFx.Analyzers/OptionMustHaveValidShortNameAnalyzer.cs

@@ -12,15 +12,15 @@ public class OptionMustHaveValidShortNameAnalyzer : AnalyzerBase
     public OptionMustHaveValidShortNameAnalyzer()
         : base(
             "Option short names must be letter characters",
-            "This option's short name must be a single letter character. " +
-            "Specified short name: `{0}`.")
-    {
-    }
+            "This option's short name must be a single letter character. "
+                + "Specified short name: `{0}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var option = CommandOptionSymbol.TryResolve(property);
         if (option is null)
@@ -32,10 +32,7 @@ public class OptionMustHaveValidShortNameAnalyzer : AnalyzerBase
         if (!char.IsLetter(option.ShortName.Value))
         {
             context.ReportDiagnostic(
-                CreateDiagnostic(
-                    propertyDeclaration.Identifier.GetLocation(),
-                    option.ShortName
-                )
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation(), option.ShortName)
             );
         }
     }

CliFx.Analyzers/OptionMustHaveValidValidatorsAnalyzer.cs

@@ -13,14 +13,14 @@ public class OptionMustHaveValidValidatorsAnalyzer : AnalyzerBase
     public OptionMustHaveValidValidatorsAnalyzer()
         : base(
             $"Option validators must derive from `{SymbolNames.CliFxBindingValidatorClass}`",
-            $"Each validator specified for this option must derive from a compatible `{SymbolNames.CliFxBindingValidatorClass}`.")
-    {
-    }
+            $"Each validator specified for this option must derive from a compatible `{SymbolNames.CliFxBindingValidatorClass}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var option = CommandOptionSymbol.TryResolve(property);
         if (option is null)
@@ -30,14 +30,17 @@ public class OptionMustHaveValidValidatorsAnalyzer : AnalyzerBase
         {
             var validatorValueType = validatorType
                 .GetBaseTypes()
-                .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingValidatorClass))?
-                .TypeArguments
+                .FirstOrDefault(
+                    t =>
+                        t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingValidatorClass)
+                )
+                ?.TypeArguments
                 .FirstOrDefault();
 
             // Value passed to the validator must be assignable from the property type
             var isCompatible =
-                validatorValueType is not null &&
-                context.Compilation.IsAssignable(property.Type, validatorValueType);
+                validatorValueType is not null
+                && context.Compilation.IsAssignable(property.Type, validatorValueType);
 
             if (!isCompatible)
             {

CliFx.Analyzers/ParameterMustBeInsideCommandAnalyzer.cs

@@ -13,14 +13,14 @@ public class ParameterMustBeInsideCommandAnalyzer : AnalyzerBase
     public ParameterMustBeInsideCommandAnalyzer()
         : base(
             "Parameters must be defined inside commands",
-            $"This parameter must be defined inside a class that implements `{SymbolNames.CliFxCommandInterface}`.")
-    {
-    }
+            $"This parameter must be defined inside a class that implements `{SymbolNames.CliFxCommandInterface}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;

CliFx.Analyzers/ParameterMustBeLastIfNonRequiredAnalyzer.cs

@@ -13,15 +13,15 @@ public class ParameterMustBeLastIfNonRequiredAnalyzer : AnalyzerBase
     public ParameterMustBeLastIfNonRequiredAnalyzer()
         : base(
             "Parameters marked as non-required must be the last in order",
-            "This parameter is non-required so it must be the last in order (its order must be highest within the command). " +
-            "Property bound to another non-required parameter: `{0}`.")
-    {
-    }
+            "This parameter is non-required so it must be the last in order (its order must be highest within the command). "
+                + "Property bound to another non-required parameter: `{0}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -37,7 +37,7 @@ public class ParameterMustBeLastIfNonRequiredAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/ParameterMustBeLastIfNonScalarAnalyzer.cs

@@ -13,15 +13,15 @@ public class ParameterMustBeLastIfNonScalarAnalyzer : AnalyzerBase
     public ParameterMustBeLastIfNonScalarAnalyzer()
         : base(
             "Parameters of non-scalar types must be the last in order",
-            "This parameter has a non-scalar type so it must be the last in order (its order must be highest within the command). " +
-            "Property bound to another non-scalar parameter: `{0}`.")
-    {
-    }
+            "This parameter has a non-scalar type so it must be the last in order (its order must be highest within the command). "
+                + "Property bound to another non-scalar parameter: `{0}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -37,7 +37,7 @@ public class ParameterMustBeLastIfNonScalarAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/ParameterMustBeRequiredIfPropertyRequiredAnalyzer.cs

@@ -0,0 +1,45 @@
+using CliFx.Analyzers.ObjectModel;
+using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CliFx.Analyzers;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class ParameterMustBeRequiredIfPropertyRequiredAnalyzer : AnalyzerBase
+{
+    public ParameterMustBeRequiredIfPropertyRequiredAnalyzer()
+        : base(
+            "Parameters bound to required properties cannot be marked as non-required",
+            "This parameter cannot be marked as non-required because it's bound to a required property."
+        ) { }
+
+    private void Analyze(
+        SyntaxNodeAnalysisContext context,
+        PropertyDeclarationSyntax propertyDeclaration,
+        IPropertySymbol property
+    )
+    {
+        if (property.ContainingType is null)
+            return;
+
+        if (!property.IsRequired())
+            return;
+
+        var parameter = CommandParameterSymbol.TryResolve(property);
+        if (parameter is null)
+            return;
+
+        if (parameter.IsRequired != false)
+            return;
+
+        context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.Identifier.GetLocation()));
+    }
+
+    public override void Initialize(AnalysisContext context)
+    {
+        base.Initialize(context);
+        context.HandlePropertyDeclaration(Analyze);
+    }
+}

CliFx.Analyzers/ParameterMustBeSingleIfNonRequiredAnalyzer.cs

@@ -13,15 +13,15 @@ public class ParameterMustBeSingleIfNonRequiredAnalyzer : AnalyzerBase
     public ParameterMustBeSingleIfNonRequiredAnalyzer()
         : base(
             "Parameters marked as non-required are limited to one per command",
-            "This parameter is non-required so it must be the only such parameter in the command. " +
-            "Property bound to another non-required parameter: `{0}`.")
-    {
-    }
+            "This parameter is non-required so it must be the only such parameter in the command. "
+                + "Property bound to another non-required parameter: `{0}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -37,7 +37,7 @@ public class ParameterMustBeSingleIfNonRequiredAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/ParameterMustBeSingleIfNonScalarAnalyzer.cs

@@ -13,15 +13,15 @@ public class ParameterMustBeSingleIfNonScalarAnalyzer : AnalyzerBase
     public ParameterMustBeSingleIfNonScalarAnalyzer()
         : base(
             "Parameters of non-scalar types are limited to one per command",
-            "This parameter has a non-scalar type so it must be the only such parameter in the command. " +
-            "Property bound to another non-scalar parameter: `{0}`.")
-    {
-    }
+            "This parameter has a non-scalar type so it must be the only such parameter in the command. "
+                + "Property bound to another non-scalar parameter: `{0}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -37,7 +37,7 @@ public class ParameterMustBeSingleIfNonScalarAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/ParameterMustHaveUniqueNameAnalyzer.cs

@@ -14,16 +14,16 @@ public class ParameterMustHaveUniqueNameAnalyzer : AnalyzerBase
     public ParameterMustHaveUniqueNameAnalyzer()
         : base(
             "Parameters must have unique names",
-            "This parameter's name must be unique within the command (comparison IS NOT case sensitive). " +
-            "Specified name: `{0}`. " +
-            "Property bound to another parameter with the same name: `{1}`.")
-    {
-    }
+            "This parameter's name must be unique within the command (comparison IS NOT case sensitive). "
+                + "Specified name: `{0}`. "
+                + "Property bound to another parameter with the same name: `{1}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -39,7 +39,7 @@ public class ParameterMustHaveUniqueNameAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)
@@ -51,7 +51,13 @@ public class ParameterMustHaveUniqueNameAnalyzer : AnalyzerBase
             if (string.IsNullOrWhiteSpace(otherParameter.Name))
                 continue;
 
-            if (string.Equals(parameter.Name, otherParameter.Name, StringComparison.OrdinalIgnoreCase))
+            if (
+                string.Equals(
+                    parameter.Name,
+                    otherParameter.Name,
+                    StringComparison.OrdinalIgnoreCase
+                )
+            )
             {
                 context.ReportDiagnostic(
                     CreateDiagnostic(

CliFx.Analyzers/ParameterMustHaveUniqueOrderAnalyzer.cs

@@ -13,16 +13,16 @@ public class ParameterMustHaveUniqueOrderAnalyzer : AnalyzerBase
     public ParameterMustHaveUniqueOrderAnalyzer()
         : base(
             "Parameters must have unique order",
-            "This parameter's order must be unique within the command. " +
-            "Specified order: {0}. " +
-            "Property bound to another parameter with the same order: `{1}`.")
-    {
-    }
+            "This parameter's order must be unique within the command. "
+                + "Specified order: {0}. "
+                + "Property bound to another parameter with the same order: `{1}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         if (property.ContainingType is null)
             return;
@@ -35,7 +35,7 @@ public class ParameterMustHaveUniqueOrderAnalyzer : AnalyzerBase
             .ContainingType
             .GetMembers()
             .OfType<IPropertySymbol>()
-            .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+            .Where(m => !m.Equals(property))
             .ToArray();
 
         foreach (var otherProperty in otherProperties)

CliFx.Analyzers/ParameterMustHaveValidConverterAnalyzer.cs

@@ -13,14 +13,14 @@ public class ParameterMustHaveValidConverterAnalyzer : AnalyzerBase
     public ParameterMustHaveValidConverterAnalyzer()
         : base(
             $"Parameter converters must derive from `{SymbolNames.CliFxBindingConverterClass}`",
-            $"Converter specified for this parameter must derive from a compatible `{SymbolNames.CliFxBindingConverterClass}`.")
-    {
-    }
+            $"Converter specified for this parameter must derive from a compatible `{SymbolNames.CliFxBindingConverterClass}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var parameter = CommandParameterSymbol.TryResolve(property);
         if (parameter is null)
@@ -32,18 +32,24 @@ public class ParameterMustHaveValidConverterAnalyzer : AnalyzerBase
         var converterValueType = parameter
             .ConverterType
             .GetBaseTypes()
-            .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingConverterClass))?
-            .TypeArguments
+            .FirstOrDefault(
+                t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingConverterClass)
+            )
+            ?.TypeArguments
             .FirstOrDefault();
 
         // Value returned by the converter must be assignable to the property type
         var isCompatible =
-            converterValueType is not null && (parameter.IsScalar()
+            converterValueType is not null
+            && (
+                parameter.IsScalar()
                     // Scalar
                     ? context.Compilation.IsAssignable(converterValueType, property.Type)
                     // Non-scalar (assume we can handle all IEnumerable types for simplicity)
-                : property.Type.TryGetEnumerableUnderlyingType() is { } enumerableUnderlyingType &&
-                  context.Compilation.IsAssignable(converterValueType, enumerableUnderlyingType)
+                    : property.Type.TryGetEnumerableUnderlyingType() is { } enumerableUnderlyingType
+                        && context
+                            .Compilation
+                            .IsAssignable(converterValueType, enumerableUnderlyingType)
             );
 
         if (!isCompatible)

CliFx.Analyzers/ParameterMustHaveValidValidatorsAnalyzer.cs

@@ -13,14 +13,14 @@ public class ParameterMustHaveValidValidatorsAnalyzer : AnalyzerBase
     public ParameterMustHaveValidValidatorsAnalyzer()
         : base(
             $"Parameter validators must derive from `{SymbolNames.CliFxBindingValidatorClass}`",
-            $"Each validator specified for this parameter must derive from a compatible `{SymbolNames.CliFxBindingValidatorClass}`.")
-    {
-    }
+            $"Each validator specified for this parameter must derive from a compatible `{SymbolNames.CliFxBindingValidatorClass}`."
+        ) { }
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
         PropertyDeclarationSyntax propertyDeclaration,
-        IPropertySymbol property)
+        IPropertySymbol property
+    )
     {
         var parameter = CommandParameterSymbol.TryResolve(property);
         if (parameter is null)
@@ -30,14 +30,17 @@ public class ParameterMustHaveValidValidatorsAnalyzer : AnalyzerBase
         {
             var validatorValueType = validatorType
                 .GetBaseTypes()
-                .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingValidatorClass))?
-                .TypeArguments
+                .FirstOrDefault(
+                    t =>
+                        t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingValidatorClass)
+                )
+                ?.TypeArguments
                 .FirstOrDefault();
 
             // Value passed to the validator must be assignable from the property type
             var isCompatible =
-                validatorValueType is not null &&
-                context.Compilation.IsAssignable(property.Type, validatorValueType);
+                validatorValueType is not null
+                && context.Compilation.IsAssignable(property.Type, validatorValueType);
 
             if (!isCompatible)
             {

CliFx.Analyzers/SystemConsoleShouldBeAvoidedAnalyzer.cs

@@ -15,13 +15,13 @@ public class SystemConsoleShouldBeAvoidedAnalyzer : AnalyzerBase
         : base(
             $"Avoid calling `System.Console` where `{SymbolNames.CliFxConsoleInterface}` is available",
             $"Use the provided `{SymbolNames.CliFxConsoleInterface}` abstraction instead of `System.Console` to ensure that the command can be tested in isolation.",
-            DiagnosticSeverity.Warning)
-    {
-    }
+            DiagnosticSeverity.Warning
+        ) { }
 
     private MemberAccessExpressionSyntax? TryGetSystemConsoleMemberAccess(
         SyntaxNodeAnalysisContext context,
-        SyntaxNode node)
+        SyntaxNode node
+    )
     {
         var currentNode = node;
 
@@ -65,9 +65,7 @@ public class SystemConsoleShouldBeAvoidedAnalyzer : AnalyzerBase
 
         if (isConsoleInterfaceAvailable)
         {
-            context.ReportDiagnostic(
-                CreateDiagnostic(systemConsoleMemberAccess.GetLocation())
-            );
+            context.ReportDiagnostic(CreateDiagnostic(systemConsoleMemberAccess.GetLocation()));
         }
     }
 

CliFx.Analyzers/Utils/Extensions/RoslynExtensions.cs

@@ -29,19 +29,40 @@ internal static class RoslynExtensions
         }
     }
 
-    public static ITypeSymbol? TryGetEnumerableUnderlyingType(this ITypeSymbol type) => type
-        .AllInterfaces
-        .FirstOrDefault(i => i.ConstructedFrom.SpecialType == SpecialType.System_Collections_Generic_IEnumerable_T)?
-        .TypeArguments[0];
+    public static ITypeSymbol? TryGetEnumerableUnderlyingType(this ITypeSymbol type) =>
+        type.AllInterfaces
+            .FirstOrDefault(
+                i =>
+                    i.ConstructedFrom.SpecialType
+                    == SpecialType.System_Collections_Generic_IEnumerable_T
+            )
+            ?.TypeArguments[0];
 
-    public static bool IsAssignable(this Compilation compilation, ITypeSymbol source, ITypeSymbol destination) =>
-        compilation.ClassifyConversion(source, destination).Exists;
+    // Detect if the property is required through roundabout means so as to not have to take dependency
+    // on higher versions of the C# compiler.
+    public static bool IsRequired(this IPropertySymbol property) =>
+        property
+            // Can't rely on the RequiredMemberAttribute because it's generated by the compiler, not added by the user,
+            // so we have to check for the presence of the `required` modifier in the syntax tree instead.
+            .DeclaringSyntaxReferences
+            .Select(r => r.GetSyntax())
+            .OfType<PropertyDeclarationSyntax>()
+            .SelectMany(p => p.Modifiers)
+            .Any(m => m.IsKind((SyntaxKind)8447));
+
+    public static bool IsAssignable(
+        this Compilation compilation,
+        ITypeSymbol source,
+        ITypeSymbol destination
+    ) => compilation.ClassifyConversion(source, destination).Exists;
 
     public static void HandleClassDeclaration(
         this AnalysisContext analysisContext,
-        Action<SyntaxNodeAnalysisContext, ClassDeclarationSyntax, ITypeSymbol> analyze)
+        Action<SyntaxNodeAnalysisContext, ClassDeclarationSyntax, ITypeSymbol> analyze
+    )
     {
-        analysisContext.RegisterSyntaxNodeAction(ctx =>
+        analysisContext.RegisterSyntaxNodeAction(
+            ctx =>
             {
                 if (ctx.Node is not ClassDeclarationSyntax classDeclaration)
                     return;
@@ -51,14 +72,18 @@ internal static class RoslynExtensions
                     return;
 
                 analyze(ctx, classDeclaration, type);
-        }, SyntaxKind.ClassDeclaration);
+            },
+            SyntaxKind.ClassDeclaration
+        );
     }
 
     public static void HandlePropertyDeclaration(
         this AnalysisContext analysisContext,
-        Action<SyntaxNodeAnalysisContext, PropertyDeclarationSyntax, IPropertySymbol> analyze)
+        Action<SyntaxNodeAnalysisContext, PropertyDeclarationSyntax, IPropertySymbol> analyze
+    )
     {
-        analysisContext.RegisterSyntaxNodeAction(ctx =>
+        analysisContext.RegisterSyntaxNodeAction(
+            ctx =>
             {
                 if (ctx.Node is not PropertyDeclarationSyntax propertyDeclaration)
                     return;
@@ -68,6 +93,8 @@ internal static class RoslynExtensions
                     return;
 
                 analyze(ctx, propertyDeclaration, property);
-        }, SyntaxKind.PropertyDeclaration);
+            },
+            SyntaxKind.PropertyDeclaration
+        );
     }
 }

CliFx.Analyzers/Utils/Extensions/StringExtensions.cs

@@ -7,10 +7,11 @@ internal static class StringExtensions
     public static string TrimEnd(
         this string str,
         string sub,
-        StringComparison comparison = StringComparison.Ordinal)
+        StringComparison comparison = StringComparison.Ordinal
+    )
     {
         while (str.EndsWith(sub, comparison))
-            str = str.Substring(0, str.Length - sub.Length);
+            str = str[..^sub.Length];
 
         return str;
     }

CliFx.Benchmarks/Benchmarks.Clipr.cs

@@ -16,9 +16,7 @@ public partial class Benchmarks
         [NamedArgument('b', "bool", Constraint = NumArgsConstraint.Optional, Const = true)]
         public bool BoolOption { get; set; }
 
-        public void Execute()
-        {
-        }
+        public void Execute() { }
     }
 
     [Benchmark(Description = "Clipr")]

CliFx.Benchmarks/Benchmarks.Cocona.cs

@@ -8,14 +8,10 @@ public partial class Benchmarks
     public class CoconaCommand
     {
         public void Execute(
-            [Option("str", new []{'s'})]
-            string? strOption,
-            [Option("int", new []{'i'})]
-            int intOption,
-            [Option("bool", new []{'b'})]
-            bool boolOption)
-        {
-        }
+            [Option("str", new[] { 's' })] string? strOption,
+            [Option("int", new[] { 'i' })] int intOption,
+            [Option("bool", new[] { 'b' })] bool boolOption
+        ) { }
     }
 
     [Benchmark(Description = "Cocona")]

CliFx.Benchmarks/Benchmarks.CommandLineParser.cs

@@ -16,9 +16,7 @@ public partial class Benchmarks
         [Option('b', "bool")]
         public bool BoolOption { get; set; }
 
-        public void Execute()
-        {
-        }
+        public void Execute() { }
     }
 
     [Benchmark(Description = "CommandLineParser")]

CliFx.Benchmarks/Benchmarks.PowerArgs.cs

@@ -16,9 +16,7 @@ public partial class Benchmarks
         [ArgShortcut("--bool"), ArgShortcut("-b")]
         public bool BoolOption { get; set; }
 
-        public void Main()
-        {
-        }
+        public void Main() { }
     }
 
     [Benchmark(Description = "PowerArgs")]

CliFx.Benchmarks/Benchmarks.SystemCommandLine.cs

@@ -15,18 +15,9 @@ public partial class Benchmarks
         {
             var command = new RootCommand
             {
-                new Option(new[] {"--str", "-s"})
-                {
-                    Argument = new Argument<string?>()
-                },
-                new Option(new[] {"--int", "-i"})
-                {
-                    Argument = new Argument<int>()
-                },
-                new Option(new[] {"--bool", "-b"})
-                {
-                    Argument = new Argument<bool>()
-                }
+                new Option(new[] { "--str", "-s" }) { Argument = new Argument<string?>() },
+                new Option(new[] { "--int", "-i" }) { Argument = new Argument<int>() },
+                new Option(new[] { "--bool", "-b" }) { Argument = new Argument<bool>() }
             };
 
             command.Handler = CommandHandler.Create(

CliFx.Benchmarks/Benchmarks.cs

@@ -11,9 +11,8 @@ public partial class Benchmarks
 {
     private static readonly string[] Arguments = { "--str", "hello world", "-i", "13", "-b" };
 
-    public static void Main() => BenchmarkRunner.Run<Benchmarks>(
-        DefaultConfig
-            .Instance
-            .WithOptions(ConfigOptions.DisableOptimizationsValidator)
+    public static void Main() =>
+        BenchmarkRunner.Run<Benchmarks>(
+            DefaultConfig.Instance.WithOptions(ConfigOptions.DisableOptimizationsValidator)
         );
 }

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -2,16 +2,17 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.13.10" />
     <PackageReference Include="clipr" Version="1.6.1" />
-    <PackageReference Include="Cocona" Version="2.0.3" />
+    <PackageReference Include="Cocona" Version="2.2.0" />
     <PackageReference Include="CommandLineParser" Version="2.9.1" />
-    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="4.0.1" />
-    <PackageReference Include="PowerArgs" Version="3.6.0" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.26.1" PrivateAssets="all" />
+    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="4.1.0" />
+    <PackageReference Include="PowerArgs" Version="4.0.3" />
     <PackageReference Include="System.CommandLine" Version="2.0.0-beta1.20574.7" />
   </ItemGroup>
 

CliFx.Demo/CliFx.Demo.csproj

@@ -2,12 +2,13 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
+    <ApplicationIcon>../favicon.ico</ApplicationIcon>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="6.0.0" />
-    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.26.1" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Demo/Commands/BookAddCommand.cs

@@ -8,16 +8,16 @@ using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands;
 
-[Command("book add", Description = "Add a book to the library.")]
+[Command("book add", Description = "Adds a book to the library.")]
 public partial class BookAddCommand : ICommand
 {
     private readonly LibraryProvider _libraryProvider;
 
     [CommandParameter(0, Name = "title", Description = "Book title.")]
-    public string Title { get; init; } = "";
+    public required string Title { get; init; }
 
-    [CommandOption("author", 'a', IsRequired = true, Description = "Book author.")]
-    public string Author { get; init; } = "";
+    [CommandOption("author", 'a', Description = "Book author.")]
+    public required string Author { get; init; }
 
     [CommandOption("published", 'p', Description = "Book publish date.")]
     public DateTimeOffset Published { get; init; } = CreateRandomDate();
@@ -49,7 +49,8 @@ public partial class BookAddCommand
 {
     private static readonly Random Random = new();
 
-    private static DateTimeOffset CreateRandomDate() => new(
+    private static DateTimeOffset CreateRandomDate() =>
+        new(
             Random.Next(1800, 2020),
             Random.Next(1, 12),
             Random.Next(1, 28),
@@ -59,7 +60,8 @@ public partial class BookAddCommand
             TimeSpan.Zero
         );
 
-    private static Isbn CreateRandomIsbn() => new(
+    private static Isbn CreateRandomIsbn() =>
+        new(
             Random.Next(0, 999),
             Random.Next(0, 99),
             Random.Next(0, 99999),

CliFx.Demo/Commands/BookCommand.cs

@@ -7,13 +7,13 @@ using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands;
 
-[Command("book", Description = "Retrieve a book from the library.")]
+[Command("book", Description = "Retrieves a book from the library.")]
 public class BookCommand : ICommand
 {
     private readonly LibraryProvider _libraryProvider;
 
     [CommandParameter(0, Name = "title", Description = "Title of the book to retrieve.")]
-    public string Title { get; init; } = "";
+    public required string Title { get; init; }
 
     public BookCommand(LibraryProvider libraryProvider)
     {

CliFx.Demo/Commands/BookListCommand.cs

@@ -6,7 +6,7 @@ using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands;
 
-[Command("book list", Description = "List all books in the library.")]
+[Command("book list", Description = "Lists all books in the library.")]
 public class BookListCommand : ICommand
 {
     private readonly LibraryProvider _libraryProvider;

CliFx.Demo/Commands/BookRemoveCommand.cs

@@ -6,13 +6,13 @@ using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands;
 
-[Command("book remove", Description = "Remove a book from the library.")]
+[Command("book remove", Description = "Removes a book from the library.")]
 public class BookRemoveCommand : ICommand
 {
     private readonly LibraryProvider _libraryProvider;
 
     [CommandParameter(0, Name = "title", Description = "Title of the book to remove.")]
-    public string Title { get; init; } = "";
+    public required string Title { get; init; }
 
     public BookRemoveCommand(LibraryProvider libraryProvider)
     {

CliFx.Demo/Domain/Book.cs

@@ -2,21 +2,4 @@
 
 namespace CliFx.Demo.Domain;
 
-public class Book
-{
-    public string Title { get; }
-
-    public string Author { get; }
-
-    public DateTimeOffset Published { get; }
-
-    public Isbn Isbn { get; }
-
-    public Book(string title, string author, DateTimeOffset published, Isbn isbn)
-    {
-        Title = title;
-        Author = author;
-        Published = published;
-        Isbn = isbn;
-    }
-}
+public record Book(string Title, string Author, DateTimeOffset Published, Isbn Isbn);

CliFx.Demo/Domain/Isbn.cs

@@ -2,32 +2,19 @@
 
 namespace CliFx.Demo.Domain;
 
-public partial class Isbn
+public partial record Isbn(
+    int EanPrefix,
+    int RegistrationGroup,
+    int Registrant,
+    int Publication,
+    int CheckDigit
+)
 {
-    public int EanPrefix { get; }
-
-    public int RegistrationGroup { get; }
-
-    public int Registrant { get; }
-
-    public int Publication { get; }
-
-    public int CheckDigit { get; }
-
-    public Isbn(int eanPrefix, int registrationGroup, int registrant, int publication, int checkDigit)
-    {
-        EanPrefix = eanPrefix;
-        RegistrationGroup = registrationGroup;
-        Registrant = registrant;
-        Publication = publication;
-        CheckDigit = checkDigit;
-    }
-
     public override string ToString() =>
         $"{EanPrefix:000}-{RegistrationGroup:00}-{Registrant:00000}-{Publication:00}-{CheckDigit:0}";
 }
 
-public partial class Isbn
+public partial record Isbn
 {
     public static Isbn Parse(string value, IFormatProvider formatProvider)
     {

CliFx.Demo/Domain/Library.cs

@@ -4,15 +4,8 @@ using System.Linq;
 
 namespace CliFx.Demo.Domain;
 
-public partial class Library
+public partial record Library(IReadOnlyList<Book> Books)
 {
-    public IReadOnlyList<Book> Books { get; }
-
-    public Library(IReadOnlyList<Book> books)
-    {
-        Books = books;
-    }
-
     public Library WithBook(Book book)
     {
         var books = Books.ToList();
@@ -29,7 +22,7 @@ public partial class Library
     }
 }
 
-public partial class Library
+public partial record Library
 {
     public static Library Empty { get; } = new(Array.Empty<Book>());
 }

CliFx.Demo/Domain/LibraryProvider.cs

@@ -1,16 +1,17 @@
 using System.IO;
 using System.Linq;
-using Newtonsoft.Json;
+using System.Text.Json;
 
 namespace CliFx.Demo.Domain;
 
 public class LibraryProvider
 {
-    private static string StorageFilePath { get; } = Path.Combine(Directory.GetCurrentDirectory(), "Library.json");
+    private static string StorageFilePath { get; } =
+        Path.Combine(Directory.GetCurrentDirectory(), "Library.json");
 
     private void StoreLibrary(Library library)
     {
-        var data = JsonConvert.SerializeObject(library);
+        var data = JsonSerializer.Serialize(library);
         File.WriteAllText(StorageFilePath, data);
     }
 
@@ -21,10 +22,11 @@ public class LibraryProvider
 
         var data = File.ReadAllText(StorageFilePath);
 
-        return JsonConvert.DeserializeObject<Library>(data) ?? Library.Empty;
+        return JsonSerializer.Deserialize<Library>(data) ?? Library.Empty;
     }
 
-    public Book? TryGetBook(string title) => GetLibrary().Books.FirstOrDefault(b => b.Title == title);
+    public Book? TryGetBook(string title) =>
+        GetLibrary().Books.FirstOrDefault(b => b.Title == title);
 
     public void AddBook(Book book)
     {

CliFx.Demo/Program.cs

@@ -1,25 +1,21 @@
 using CliFx;
-using CliFx.Demo.Commands;
 using CliFx.Demo.Domain;
 using Microsoft.Extensions.DependencyInjection;
 
-// We use Microsoft.Extensions.DependencyInjection for injecting dependencies in commands
-var services = new ServiceCollection();
-
-// Register services
-services.AddSingleton<LibraryProvider>();
-
-// Register commands
-services.AddTransient<BookCommand>();
-services.AddTransient<BookAddCommand>();
-services.AddTransient<BookRemoveCommand>();
-services.AddTransient<BookListCommand>();
-
-var serviceProvider = services.BuildServiceProvider();
-
 return await new CliApplicationBuilder()
     .SetDescription("Demo application showcasing CliFx features.")
     .AddCommandsFromThisAssembly()
-    .UseTypeActivator(serviceProvider.GetRequiredService)
+    .UseTypeActivator(commandTypes =>
+    {
+        // We use Microsoft.Extensions.DependencyInjection for injecting dependencies in commands
+        var services = new ServiceCollection();
+        services.AddSingleton<LibraryProvider>();
+
+        // Register all commands as transient services
+        foreach (var commandType in commandTypes)
+            services.AddTransient(commandType);
+
+        return services.BuildServiceProvider();
+    })
     .Build()
     .RunAsync();

CliFx.Demo/Readme.md

@@ -1,5 +1,5 @@
 # CliFx Demo Project
 
-Sample command line interface for managing a library of books.
+Sample command-line interface for managing a library of books.
 
-This demo project showcases basic CliFx functionality such as command routing, argument parsing, autogenerated help text.
+This demo project showcases basic CliFx functionality such as command routing, argument parsing, and autogenerated help text.

CliFx.Tests.Dummy/CliFx.Tests.Dummy.csproj

@@ -2,9 +2,14 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
+    <ApplicationIcon>../favicon.ico</ApplicationIcon>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="CSharpier.MsBuild" Version="0.26.1" PrivateAssets="all" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\CliFx\CliFx.csproj" />
     <ProjectReference Include="..\CliFx.Analyzers\CliFx.Analyzers.csproj" ReferenceOutputAssembly="false" OutputItemType="analyzer" />

CliFx.Tests.Dummy/Commands/CancellationTestCommand.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Tests.Dummy.Commands;
+
+[Command("cancel-test")]
+public class CancellationTestCommand : ICommand
+{
+    public async ValueTask ExecuteAsync(IConsole console)
+    {
+        try
+        {
+            console.Output.WriteLine("Started.");
+
+            await Task.Delay(TimeSpan.FromSeconds(3), console.RegisterCancellationHandler());
+
+            console.Output.WriteLine("Completed.");
+        }
+        catch (OperationCanceledException)
+        {
+            console.Output.WriteLine("Cancelled.");
+            throw;
+        }
+    }
+}

CliFx.Tests.Dummy/Commands/EnvironmentTestCommand.cs

@@ -8,7 +8,7 @@ namespace CliFx.Tests.Dummy.Commands;
 public class EnvironmentTestCommand : ICommand
 {
     [CommandOption("target", EnvironmentVariable = "ENV_TARGET")]
-    public string GreetingTarget { get; set; } = "World";
+    public string GreetingTarget { get; init; } = "World";
 
     public ValueTask ExecuteAsync(IConsole console)
     {

CliFx.Tests.Dummy/Program.cs

@@ -1,20 +1,21 @@
 using System;
+using System.IO;
 using System.Reflection;
+using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 
 namespace CliFx.Tests.Dummy;
-// This dummy application is used in tests for scenarios
-// that require an external process to properly verify.
 
-public static partial class Program
+// This dummy application is used in tests for scenarios that require an external process to properly verify
+public static class Program
 {
-    public static Assembly Assembly { get; } = typeof(Program).Assembly;
+    // Path to the apphost
+    public static string FilePath { get; } =
+        Path.ChangeExtension(
+            Assembly.GetExecutingAssembly().Location,
+            RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "exe" : null
+        );
 
-    public static string Location { get; } = Assembly.Location;
-}
-
-public static partial class Program
-{
     public static async Task Main()
     {
         // Make sure color codes are not produced because we rely on the output in tests
@@ -23,9 +24,6 @@ public static partial class Program
             "false"
         );
 
-        await new CliApplicationBuilder()
-            .AddCommandsFromThisAssembly()
-            .Build()
-            .RunAsync();
+        await new CliApplicationBuilder().AddCommandsFromThisAssembly().Build().RunAsync();
     }
 }

CliFx.Tests/ApplicationSpecs.cs

@@ -11,12 +11,10 @@ namespace CliFx.Tests;
 public class ApplicationSpecs : SpecsBase
 {
     public ApplicationSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Application_can_be_created_with_minimal_configuration()
+    public async Task I_can_create_an_application_with_the_default_configuration()
     {
         // Act
         var app = new CliApplicationBuilder()
@@ -24,17 +22,14 @@ public class ApplicationSpecs : SpecsBase
             .UseConsole(FakeConsole)
             .Build();
 
-        var exitCode = await app.RunAsync(
-            Array.Empty<string>(),
-            new Dictionary<string, string>()
-        );
+        var exitCode = await app.RunAsync(Array.Empty<string>(), new Dictionary<string, string>());
 
         // Assert
         exitCode.Should().Be(0);
     }
 
     [Fact]
-    public async Task Application_can_be_created_with_a_fully_customized_configuration()
+    public async Task I_can_create_an_application_with_a_custom_configuration()
     {
         // Act
         var app = new CliApplicationBuilder()
@@ -53,17 +48,14 @@ public class ApplicationSpecs : SpecsBase
             .UseTypeActivator(Activator.CreateInstance!)
             .Build();
 
-        var exitCode = await app.RunAsync(
-            Array.Empty<string>(),
-            new Dictionary<string, string>()
-        );
+        var exitCode = await app.RunAsync(Array.Empty<string>(), new Dictionary<string, string>());
 
         // Assert
         exitCode.Should().Be(0);
     }
 
     [Fact]
-    public async Task Application_configuration_fails_if_an_invalid_command_is_registered()
+    public async Task I_can_try_to_create_an_application_and_get_an_error_if_it_has_invalid_commands()
     {
         // Act
         var app = new CliApplicationBuilder()
@@ -71,15 +63,12 @@ public class ApplicationSpecs : SpecsBase
             .UseConsole(FakeConsole)
             .Build();
 
-        var exitCode = await app.RunAsync(
-            Array.Empty<string>(),
-            new Dictionary<string, string>()
-        );
-
-        var stdErr = FakeConsole.ReadErrorString();
+        var exitCode = await app.RunAsync(Array.Empty<string>(), new Dictionary<string, string>());
 
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("not a valid command");
     }
 }

CliFx.Tests/CancellationSpecs.cs

@@ -1,7 +1,11 @@
 using System;
 using System.Collections.Generic;
+using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using CliWrap;
 using FluentAssertions;
 using Xunit;
 using Xunit.Abstractions;
@@ -11,17 +15,53 @@ namespace CliFx.Tests;
 public class CancellationSpecs : SpecsBase
 {
     public CancellationSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
+        : base(testOutput) { }
+
+    [Fact(Timeout = 15000)]
+    public async Task I_can_configure_the_command_to_listen_to_the_interrupt_signal()
     {
+        // Arrange
+        using var cts = new CancellationTokenSource();
+
+        // We need to send the cancellation request right after the process has registered
+        // a handler for the interrupt signal, otherwise the default handler will trigger
+        // and just kill the process.
+        void HandleStdOut(string line)
+        {
+            if (string.Equals(line, "Started.", StringComparison.OrdinalIgnoreCase))
+                cts.CancelAfter(TimeSpan.FromSeconds(0.2));
+        }
+
+        var stdOutBuffer = new StringBuilder();
+
+        var pipeTarget = PipeTarget.Merge(
+            PipeTarget.ToDelegate(HandleStdOut),
+            PipeTarget.ToStringBuilder(stdOutBuffer)
+        );
+
+        var command = Cli.Wrap(Dummy.Program.FilePath).WithArguments("cancel-test") | pipeTarget;
+
+        // Act & assert
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(
+            async () =>
+                await command.ExecuteAsync(
+                    // Forceful cancellation (not required because we have a timeout)
+                    CancellationToken.None,
+                    // Graceful cancellation
+                    cts.Token
+                )
+        );
+
+        stdOutBuffer.ToString().Trim().Should().ConsistOfLines("Started.", "Cancelled.");
     }
 
     [Fact]
-    public async Task Command_can_register_to_receive_a_cancellation_signal_from_the_console()
+    public async Task I_can_configure_the_command_to_listen_to_the_interrupt_signal_when_running_in_isolation()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
@@ -29,38 +69,42 @@ public class Command : ICommand
                 {
                     try
                     {
+                        console.Output.WriteLine("Started.");
+
                         await Task.Delay(
                             TimeSpan.FromSeconds(3),
                             console.RegisterCancellationHandler()
                         );
 
-            console.Output.WriteLine(""Completed successfully"");
+                        console.Output.WriteLine("Completed.");
                     }
                     catch (OperationCanceledException)
                     {
-            console.Output.WriteLine(""Cancelled"");
+                        console.Output.WriteLine("Cancelled.");
                         throw;
                     }
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
             .UseConsole(FakeConsole)
             .Build();
 
-        // Act
         FakeConsole.RequestCancellation(TimeSpan.FromSeconds(0.2));
 
+        // Act
         var exitCode = await application.RunAsync(
             Array.Empty<string>(),
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().NotBe(0);
-        stdOut.Trim().Should().Be("Cancelled");
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().ConsistOfLines("Started.", "Cancelled.");
     }
 }

CliFx.Tests/CliFx.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
@@ -9,16 +9,18 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Basic.Reference.Assemblies" Version="1.2.4" />
-    <PackageReference Include="CliWrap" Version="3.4.4" />
-    <PackageReference Include="FluentAssertions" Version="6.7.0" />
-    <PackageReference Include="GitHubActionsTestLogger" Version="2.0.0" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.2.0" />
-    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="6.0.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
-    <PackageReference Include="xunit" Version="2.4.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" PrivateAssets="all" />
-    <PackageReference Include="coverlet.collector" Version="3.1.2" PrivateAssets="all" />
+    <PackageReference Include="Basic.Reference.Assemblies.Net70" Version="1.4.5" />
+    <PackageReference Include="CliWrap" Version="3.6.4" />
+    <PackageReference Include="coverlet.collector" Version="6.0.0" PrivateAssets="all" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.26.1" PrivateAssets="all" />
+    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="GitHubActionsTestLogger" Version="2.3.3" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.7.0" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="8.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="PolyShim" Version="1.8.0" PrivateAssets="all" />
+    <PackageReference Include="xunit" Version="2.6.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>
@@ -26,12 +28,4 @@
     <ProjectReference Include="..\CliFx\CliFx.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <None Include="../CliFx.Tests.Dummy/bin/$(Configuration)/$(TargetFramework)/CliFx.Tests.Dummy.runtimeconfig.json">
-      <Link>CliFx.Tests.Dummy.runtimeconfig.json</Link>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      <Visible>false</Visible>
-    </None>
-  </ItemGroup>
-
 </Project>

CliFx.Tests/ConsoleSpecs.cs

@@ -17,22 +17,16 @@ namespace CliFx.Tests;
 public class ConsoleSpecs : SpecsBase
 {
     public ConsoleSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
-    [Fact]
-    public async Task Real_console_maps_directly_to_system_console()
+    [Fact(Timeout = 15000)]
+    public async Task I_can_run_the_application_with_the_default_console_implementation_to_interact_with_the_system_console()
     {
-        // Can't verify our own console output, so using an
-        // external process for this test.
+        // Can't verify our own console output, so using an external process for this test
 
         // Arrange
-        var command = "Hello world" | Cli.Wrap("dotnet")
-            .WithArguments(a => a
-                .Add(Dummy.Program.Location)
-                .Add("console-test")
-            );
+        var command =
+            "Hello world" | Cli.Wrap(Dummy.Program.FilePath).WithArguments("console-test");
 
         // Act
         var result = await command.ExecuteBufferedAsync();
@@ -43,12 +37,31 @@ public class ConsoleSpecs : SpecsBase
     }
 
     [Fact]
-    public async Task Fake_console_does_not_leak_to_system_console()
+    public void I_can_run_the_application_on_a_system_with_a_custom_console_encoding_and_not_get_corrupted_output()
+    {
+        // Arrange
+        using var buffer = new MemoryStream();
+        using var consoleWriter = new ConsoleWriter(FakeConsole, buffer, Encoding.UTF8);
+
+        // Act
+        consoleWriter.Write("Hello world");
+        consoleWriter.Flush();
+
+        // Assert
+        var outputBytes = buffer.ToArray();
+        outputBytes.Should().NotContain(Encoding.UTF8.GetPreamble());
+
+        var output = consoleWriter.Encoding.GetString(outputBytes);
+        output.Should().Be("Hello world");
+    }
+
+    [Fact]
+    public async Task I_can_run_the_application_with_the_fake_console_implementation_to_isolate_console_interactions()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
@@ -57,16 +70,19 @@ public class Command : ICommand
                     console.ResetColor();
                     console.ForegroundColor = ConsoleColor.DarkMagenta;
                     console.BackgroundColor = ConsoleColor.DarkMagenta;
+                    console.WindowWidth = 100;
+                    console.WindowHeight = 25;
                     console.CursorLeft = 42;
                     console.CursorTop = 24;
 
-        console.Output.WriteLine(""Hello "");
-        console.Error.WriteLine(""world!"");
+                    console.Output.WriteLine("Hello ");
+                    console.Error.WriteLine("world!");
 
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -90,6 +106,8 @@ public class Command : ICommand
         Console.BackgroundColor.Should().NotBe(ConsoleColor.DarkMagenta);
 
         // This fails because tests don't spawn a console window
+        //Console.WindowWidth.Should().Be(100);
+        //Console.WindowHeight.Should().Be(25);
         //Console.CursorLeft.Should().NotBe(42);
         //Console.CursorTop.Should().NotBe(24);
 
@@ -99,12 +117,12 @@ public class Command : ICommand
     }
 
     [Fact]
-    public async Task Fake_console_can_be_used_with_an_in_memory_backing_store()
+    public async Task I_can_run_the_application_with_the_fake_console_implementation_and_simulate_stream_interactions()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
@@ -117,7 +135,8 @@ public class Command : ICommand
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -132,22 +151,23 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("Hello world");
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Trim().Should().Be("Hello world");
     }
 
     [Fact]
-    public async Task Fake_console_can_read_key_presses()
+    public async Task I_can_run_the_application_with_the_fake_console_implementation_and_simulate_key_presses()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
@@ -160,7 +180,8 @@ public class Command : ICommand
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -177,31 +198,10 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Trim().Should().ConsistOfLines(
-            "D0",
-            "A",
-            "Backspace"
-        );
-    }
 
-    [Fact]
-    public void Console_does_not_emit_preamble_when_used_with_encoding_that_has_it()
-    {
-        // Arrange
-        using var buffer = new MemoryStream();
-        using var consoleWriter = new ConsoleWriter(FakeConsole, buffer, Encoding.UTF8);
-
-        // Act
-        consoleWriter.Write("Hello world");
-        consoleWriter.Flush();
-
-        var output = consoleWriter.Encoding.GetString(buffer.ToArray());
-
-        // Assert
-        output.Should().Be("Hello world");
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().ConsistOfLines("D0", "A", "Backspace");
     }
 }

CliFx.Tests/DirectivesSpecs.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using CliFx.Tests.Utils;
@@ -15,73 +14,49 @@ namespace CliFx.Tests;
 public class DirectivesSpecs : SpecsBase
 {
     public DirectivesSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
-    [Fact]
-    public async Task Debug_directive_can_be_specified_to_interrupt_execution_until_a_debugger_is_attached()
+    [Fact(Timeout = 15000)]
+    public async Task I_can_use_the_debug_directive_to_make_the_application_wait_for_the_debugger_to_attach()
     {
         // Arrange
-        var stdOutBuffer = new StringBuilder();
+        using var cts = new CancellationTokenSource();
 
-        var command = Cli.Wrap("dotnet")
-            .WithArguments(a => a
-                .Add(Dummy.Program.Location)
-                .Add("[debug]")
-            ) | stdOutBuffer;
+        // We can't actually attach a debugger, but we can ensure that the process is waiting for one
+        void HandleStdOut(string line)
+        {
+            // Kill the process once it writes the output we expect
+            if (line.Contains("Attach the debugger to", StringComparison.OrdinalIgnoreCase))
+                cts.Cancel();
+        }
 
-        // Act
+        var command = Cli.Wrap(Dummy.Program.FilePath).WithArguments("[debug]") | HandleStdOut;
+
+        // Act & assert
         try
         {
-            // This has a timeout just in case the execution hangs forever
-            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
-
-            var task = command.ExecuteAsync(cts.Token);
-
-            // We can't attach a debugger programmatically, so the application
-            // will hang indefinitely.
-            // To work around it, we will wait until the application writes
-            // something to the standard output and then kill it.
-            while (true)
+            await command.ExecuteAsync(cts.Token);
+        }
+        catch (OperationCanceledException ex) when (ex.CancellationToken == cts.Token)
         {
-                if (stdOutBuffer.Length > 0)
-                {
-                    cts.Cancel();
-                    break;
+            // This means that the process was killed after it wrote the expected output
         }
-
-                await Task.Delay(100, cts.Token);
-            }
-
-            await task;
-        }
-        catch (OperationCanceledException)
-        {
-            // This is expected
-        }
-
-        var stdOut = stdOutBuffer.ToString();
-
-        // Assert
-        stdOut.Should().Contain("Attach debugger to");
-
-        TestOutput.WriteLine(stdOut);
     }
 
     [Fact]
-    public async Task Preview_directive_can_be_specified_to_print_command_input()
+    public async Task I_can_use_the_preview_directive_to_make_the_application_print_the_parsed_command_input()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
-[Command(""cmd"")]
+            // lang=csharp
+            """
+            [Command("cmd")]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) => default;
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -92,21 +67,28 @@ public class Command : ICommand
         // Act
         var exitCode = await application.RunAsync(
             new[] { "[preview]", "cmd", "param", "-abc", "--option", "foo" },
-            new Dictionary<string, string>
-            {
-                ["ENV_QOP"] = "hello",
-                ["ENV_KIL"] = "world"
-            }
+            new Dictionary<string, string> { ["ENV_QOP"] = "hello", ["ENV_KIL"] = "world" }
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ContainAllInOrder(
-            "cmd", "<param>", "[-a]", "[-b]", "[-c]", "[--option \"foo\"]",
-            "ENV_QOP", "=", "\"hello\"",
-            "ENV_KIL", "=", "\"world\""
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "cmd",
+                "<param>",
+                "[-a]",
+                "[-b]",
+                "[-c]",
+                "[--option \"foo\"]",
+                "ENV_QOP",
+                "=",
+                "\"hello\"",
+                "ENV_KIL",
+                "=",
+                "\"world\""
             );
     }
 }

CliFx.Tests/EnvironmentSpecs.cs

@@ -15,30 +15,34 @@ namespace CliFx.Tests;
 public class EnvironmentSpecs : SpecsBase
 {
     public EnvironmentSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Option_can_fall_back_to_an_environment_variable()
+    public async Task I_can_configure_an_option_to_fall_back_to_an_environment_variable_if_the_user_does_not_provide_the_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", IsRequired = true, EnvironmentVariable = ""ENV_FOO"")]
-    public string Foo { get; set; }
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public string? Foo { get; init; }
+
+                [CommandOption("bar", EnvironmentVariable = "ENV_BAR")]
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
                     console.Output.WriteLine(Foo);
+                    console.Output.WriteLine(Bar);
+
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -47,74 +51,29 @@ public class Command : ICommand
 
         // Act
         var exitCode = await application.RunAsync(
-            Array.Empty<string>(),
-            new Dictionary<string, string>
-            {
-                ["ENV_FOO"] = "bar"
-            }
+            new[] { "--foo", "42" },
+            new Dictionary<string, string> { ["ENV_FOO"] = "100", ["ENV_BAR"] = "200" }
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Trim().Should().Be("bar");
-    }
-
-    [Fact]
-    public async Task Option_does_not_fall_back_to_an_environment_variable_if_a_value_is_provided_through_arguments()
-    {
-        // Arrange
-        var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
-[Command]
-public class Command : ICommand
-{
-    [CommandOption(""foo"", EnvironmentVariable = ""ENV_FOO"")]
-    public string Foo { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console)
-    {
-        console.Output.WriteLine(Foo);
-        return default;
-    }
-}
-");
-
-        var application = new CliApplicationBuilder()
-            .AddCommand(commandType)
-            .UseConsole(FakeConsole)
-            .Build();
-
-        // Act
-        var exitCode = await application.RunAsync(
-            new[] {"--foo", "baz"},
-            new Dictionary<string, string>
-            {
-                ["ENV_FOO"] = "bar"
-            }
-        );
 
         var stdOut = FakeConsole.ReadOutputString();
-
-        // Assert
-        exitCode.Should().Be(0);
-        stdOut.Trim().Should().Be("baz");
+        stdOut.Trim().Should().ConsistOfLines("42", "200");
     }
 
     [Fact]
-    public async Task Option_of_non_scalar_type_can_receive_multiple_values_from_an_environment_variable()
+    public async Task I_can_configure_an_option_bound_to_a_non_scalar_property_to_fall_back_to_an_environment_variable_if_the_user_does_not_provide_the_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", EnvironmentVariable = ""ENV_FOO"")]
-    public IReadOnlyList<string> Foo { get; set; }
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -124,7 +83,8 @@ public class Command : ICommand
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -134,34 +94,28 @@ public class Command : ICommand
         // Act
         var exitCode = await application.RunAsync(
             Array.Empty<string>(),
-            new Dictionary<string, string>
-            {
-                ["ENV_FOO"] = $"bar{Path.PathSeparator}baz"
-            }
+            new Dictionary<string, string> { ["ENV_FOO"] = $"bar{Path.PathSeparator}baz" }
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "bar",
-            "baz"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("bar", "baz");
     }
 
     [Fact]
-    public async Task Option_of_scalar_type_always_receives_a_single_value_from_an_environment_variable()
+    public async Task I_can_configure_an_option_bound_to_a_scalar_property_to_fall_back_to_an_environment_variable_while_ignoring_path_separators()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", EnvironmentVariable = ""ENV_FOO"")]
-    public string Foo { get; set; }
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -169,7 +123,8 @@ public class Command : ICommand
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -179,78 +134,26 @@ public class Command : ICommand
         // Act
         var exitCode = await application.RunAsync(
             Array.Empty<string>(),
-            new Dictionary<string, string>
-            {
-                ["ENV_FOO"] = $"bar{Path.PathSeparator}baz"
-            }
+            new Dictionary<string, string> { ["ENV_FOO"] = $"bar{Path.PathSeparator}baz" }
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be($"bar{Path.PathSeparator}baz");
     }
 
-    [Fact]
-    public async Task Environment_variables_are_matched_case_sensitively()
-    {
-        // Arrange
-        var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
-[Command]
-public class Command : ICommand
-{
-    [CommandOption(""foo"", EnvironmentVariable = ""ENV_FOO"")]
-    public string Foo { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console)
-    {
-        console.Output.WriteLine(Foo);
-        return default;
-    }
-}
-");
-
-        var application = new CliApplicationBuilder()
-            .AddCommand(commandType)
-            .UseConsole(FakeConsole)
-            .Build();
-
-        // Act
-        var exitCode = await application.RunAsync(
-            Array.Empty<string>(),
-            new Dictionary<string, string>
-            {
-                ["ENV_foo"] = "baz",
-                ["ENV_FOO"] = "bar",
-                ["env_FOO"] = "qop"
-            }
-        );
-
-        var stdOut = FakeConsole.ReadOutputString();
-
-        // Assert
-        exitCode.Should().Be(0);
-        stdOut.Trim().Should().Be("bar");
-    }
-
-    [Fact]
-    public async Task Environment_variables_are_extracted_automatically()
+    [Fact(Timeout = 15000)]
+    public async Task I_can_run_the_application_and_it_will_resolve_all_required_environment_variables_automatically()
     {
         // Ensures that the environment variables are properly obtained from
         // System.Environment when they are not provided explicitly to CliApplication.
 
         // Arrange
-        var command = Cli.Wrap("dotnet")
-            .WithArguments(a => a
-                .Add(Dummy.Program.Location)
-                .Add("env-test")
-            )
-            .WithEnvironmentVariables(e => e
-                .Set("ENV_TARGET", "Mars")
-            );
+        var command = Cli.Wrap(Dummy.Program.FilePath)
+            .WithArguments("env-test")
+            .WithEnvironmentVariables(e => e.Set("ENV_TARGET", "Mars"));
 
         // Act
         var result = await command.ExecuteBufferedAsync();

CliFx.Tests/ErrorReportingSpecs.cs

@@ -12,24 +12,23 @@ namespace CliFx.Tests;
 public class ErrorReportingSpecs : SpecsBase
 {
     public ErrorReportingSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Command_can_throw_an_exception_which_exits_with_a_stacktrace()
+    public async Task I_can_throw_an_exception_in_a_command_to_report_an_error_with_a_stacktrace()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) =>
-        throw new Exception(""Something went wrong"");
+                    throw new Exception("Something went wrong");
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -42,32 +41,33 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Should().BeEmpty();
-        stdErr.Should().ContainAllInOrder(
-            "System.Exception", "Something went wrong",
-            "at", "CliFx."
-        );
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr
+            .Should()
+            .ContainAllInOrder("System.Exception", "Something went wrong", "at", "CliFx.");
     }
 
     [Fact]
-    public async Task Command_can_throw_an_exception_with_an_inner_exception_which_exits_with_a_stacktrace()
+    public async Task I_can_throw_an_exception_with_an_inner_exception_in_a_command_to_report_an_error_with_a_stacktrace()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) =>
-        throw new Exception(""Something went wrong"", new Exception(""Another exception""));
+                    throw new Exception("Something went wrong", new Exception("Another exception"));
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -80,33 +80,40 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Should().BeEmpty();
-        stdErr.Should().ContainAllInOrder(
-            "System.Exception", "Something went wrong",
-            "System.Exception", "Another exception",
-            "at", "CliFx."
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr
+            .Should()
+            .ContainAllInOrder(
+                "System.Exception",
+                "Something went wrong",
+                "System.Exception",
+                "Another exception",
+                "at",
+                "CliFx."
             );
     }
 
     [Fact]
-    public async Task Command_can_throw_a_special_exception_which_exits_with_specified_code_and_message()
+    public async Task I_can_throw_an_exception_in_a_command_to_report_an_error_and_exit_with_the_specified_code()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) =>
-        throw new CommandException(""Something went wrong"", 69);
+                    throw new CommandException("Something went wrong", 69);
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -119,29 +126,31 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().Be(69);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Should().BeEmpty();
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Trim().Should().Be("Something went wrong");
     }
 
     [Fact]
-    public async Task Command_can_throw_a_special_exception_without_message_which_exits_with_a_stacktrace()
+    public async Task I_can_throw_an_exception_without_a_message_in_a_command_to_report_an_error_with_a_stacktrace()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) =>
-        throw new CommandException("""", 69);
+                    throw new CommandException("", 69);
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -154,32 +163,31 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().Be(69);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Should().BeEmpty();
-        stdErr.Should().ContainAllInOrder(
-            "CliFx.Exceptions.CommandException",
-            "at", "CliFx."
-        );
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().ContainAllInOrder("CliFx.Exceptions.CommandException", "at", "CliFx.");
     }
 
     [Fact]
-    public async Task Command_can_throw_a_special_exception_which_prints_help_text_before_exiting()
+    public async Task I_can_throw_an_exception_in_a_command_to_report_an_error_and_print_the_help_text()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console) =>
-        throw new CommandException(""Something went wrong"", 69, true);
+                    throw new CommandException("Something went wrong", 69, true);
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -193,12 +201,13 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().Be(69);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Should().Contain("This will be in help text");
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Trim().Should().Be("Something went wrong");
     }
 }

CliFx.Tests/OptionBindingSpecs.cs

@@ -12,29 +12,29 @@ namespace CliFx.Tests;
 public class OptionBindingSpecs : SpecsBase
 {
     public OptionBindingSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Option_is_bound_from_an_argument_matching_its_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_by_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public bool Foo { get; set; }
+                [CommandOption("foo")]
+                public bool Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
                     console.Output.WriteLine(Foo);
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -47,32 +47,34 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("True");
     }
 
     [Fact]
-    public async Task Option_is_bound_from_an_argument_matching_its_short_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_by_short_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandOption('f')]
-    public bool Foo { get; set; }
+                public bool Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
                     console.Output.WriteLine(Foo);
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -80,42 +82,41 @@ public class Command : ICommand
             .Build();
 
         // Act
-        var exitCode = await application.RunAsync(
-            new[] {"-f"},
-            new Dictionary<string, string>()
-        );
-
-        var stdOut = FakeConsole.ReadOutputString();
+        var exitCode = await application.RunAsync(new[] { "-f" }, new Dictionary<string, string>());
 
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("True");
     }
 
     [Fact]
-    public async Task Option_is_bound_from_a_set_of_arguments_matching_its_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_set_by_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
-    [CommandOption(""bar"")]
-    public string Bar { get; set; }
+                [CommandOption("bar")]
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -128,40 +129,39 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = one",
-            "Bar = two"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = two");
     }
 
     [Fact]
-    public async Task Option_is_bound_from_a_set_of_arguments_matching_its_short_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_set_by_short_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 [CommandOption('b')]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -174,40 +174,39 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = one",
-            "Bar = two"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = two");
     }
 
     [Fact]
-    public async Task Option_is_bound_from_a_stack_of_arguments_matching_its_short_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_stack_by_short_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandOption('f')]
-    public string Foo { get; set; }
+                public string? Foo { get; init; }
 
                 [CommandOption('b')]
-    public string Bar { get; set; }
+                public string? Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -220,28 +219,25 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = ",
-            "Bar = value"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = ", "Bar = value");
     }
 
     [Fact]
-    public async Task Option_of_non_scalar_type_is_bound_from_a_set_of_arguments_matching_its_name()
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_arguments_by_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""Foo"")]
-    public IReadOnlyList<string> Foo { get; set; }
+                [CommandOption("Foo")]
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -250,7 +246,9 @@ public class Command : ICommand
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -263,29 +261,25 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "one",
-            "two",
-            "three"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
     }
 
     [Fact]
-    public async Task Option_of_non_scalar_type_is_bound_from_a_set_of_arguments_matching_its_short_name()
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_arguments_by_short_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandOption('f')]
-    public IReadOnlyList<string> Foo { get; set; }
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -294,7 +288,9 @@ public class Command : ICommand
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -307,29 +303,25 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "one",
-            "two",
-            "three"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
     }
 
     [Fact]
-    public async Task Option_of_non_scalar_type_is_bound_from_multiple_sets_of_arguments_matching_its_name()
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_argument_sets_by_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public IReadOnlyList<string> Foo { get; set; }
+                [CommandOption("foo")]
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -338,7 +330,9 @@ public class Command : ICommand
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -351,29 +345,25 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "one",
-            "two",
-            "three"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
     }
 
     [Fact]
-    public async Task Option_of_non_scalar_type_is_bound_from_multiple_sets_of_arguments_matching_its_short_name()
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_argument_sets_by_short_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandOption('f')]
-    public IReadOnlyList<string> Foo { get; set; }
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -382,7 +372,9 @@ public class Command : ICommand
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -395,29 +387,25 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "one",
-            "two",
-            "three"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
     }
 
     [Fact]
-    public async Task Option_of_non_scalar_type_is_bound_from_multiple_sets_of_arguments_matching_its_name_or_short_name()
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_argument_sets_by_name_or_short_name()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", 'f')]
-    public IReadOnlyList<string> Foo { get; set; }
+                [CommandOption("foo", 'f')]
+                public IReadOnlyList<string>? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
@@ -426,7 +414,9 @@ public class Command : ICommand
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -439,41 +429,39 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "one",
-            "two",
-            "three"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
     }
 
     [Fact]
-    public async Task Option_is_not_bound_if_there_are_no_arguments_matching_its_name_or_short_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_no_value_if_the_user_does_not_provide_the_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
-    [CommandOption(""bar"")]
-    public string Bar { get; set; } = ""hello"";
+                [CommandOption("bar")]
+                public string? Bar { get; init; } = "hello";
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -486,23 +474,20 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = one",
-            "Bar = hello"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = hello");
     }
 
     [Fact]
-    public async Task Option_binding_supports_multiple_inheritance_through_default_interface_members()
+    public async Task I_can_bind_an_option_to_a_property_through_multiple_inheritance()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             public static class SharedContext
             {
                 public static int Foo { get; set; }
@@ -512,45 +497,46 @@ public static class SharedContext
 
             public interface IHasFoo : ICommand
             {
-    [CommandOption(""foo"")]
+                [CommandOption("foo")]
                 public int Foo
                 {
                     get => SharedContext.Foo;
-        set => SharedContext.Foo = value;
+                    init => SharedContext.Foo = value;
                 }
             }
 
             public interface IHasBar : ICommand
             {
-    [CommandOption(""bar"")]
+                [CommandOption("bar")]
                 public bool Bar
                 {
                     get => SharedContext.Bar;
-        set => SharedContext.Bar = value;
+                    init => SharedContext.Bar = value;
                 }
             }
 
             public interface IHasBaz : ICommand
             {
-    public string Baz { get; set; }
+                public string? Baz { get; init; }
             }
 
             [Command]
             public class Command : IHasFoo, IHasBar, IHasBaz
             {
-    [CommandOption(""baz"")]
-    public string Baz { get; set; }
+                [CommandOption("baz")]
+                public string? Baz { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + SharedContext.Foo);
-        console.Output.WriteLine(""Bar = "" + SharedContext.Bar);
-        console.Output.WriteLine(""Baz = "" + Baz);
+                    console.Output.WriteLine("Foo = " + SharedContext.Foo);
+                    console.Output.WriteLine("Bar = " + SharedContext.Bar);
+                    console.Output.WriteLine("Baz = " + Baz);
 
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -558,41 +544,36 @@ public class Command : IHasFoo, IHasBar, IHasBaz
             .Build();
 
         // Act
-        var exitCode = await application.RunAsync(
-            new[] { "--foo", "42", "--bar", "--baz", "xyz" }
-        );
-
-        var stdOut = FakeConsole.ReadOutputString();
+        var exitCode = await application.RunAsync(new[] { "--foo", "42", "--bar", "--baz", "xyz" });
 
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = 42",
-            "Bar = True",
-            "Baz = xyz"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = 42", "Bar = True", "Baz = xyz");
     }
 
     [Fact]
-    public async Task Option_binding_does_not_consider_a_negative_number_as_an_option_name_or_short_name()
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_correct_value_if_the_user_provides_an_argument_containing_a_negative_number()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
                     console.Output.WriteLine(Foo);
-
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -605,28 +586,30 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("-13");
     }
 
     [Fact]
-    public async Task Option_binding_fails_if_a_required_option_has_not_been_provided()
+    public async Task I_can_try_to_bind_a_required_option_to_a_property_and_get_an_error_if_the_user_does_not_provide_the_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", IsRequired = true)]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -639,28 +622,30 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Missing required option(s)");
     }
 
     [Fact]
-    public async Task Option_binding_fails_if_a_required_option_has_been_provided_with_an_empty_value()
+    public async Task I_can_try_to_bind_a_required_option_to_a_property_and_get_an_error_if_the_user_provides_an_empty_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", IsRequired = true)]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public required string Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -673,28 +658,30 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Missing required option(s)");
     }
 
     [Fact]
-    public async Task Option_binding_fails_if_a_required_option_of_non_scalar_type_has_not_been_provided_with_at_least_one_value()
+    public async Task I_can_try_to_bind_an_option_to_a_non_scalar_property_and_get_an_error_if_the_user_does_not_provide_at_least_one_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"", IsRequired = true)]
-    public IReadOnlyList<string> Foo { get; set; }
+                [CommandOption("foo")]
+                public required IReadOnlyList<string> Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -707,28 +694,30 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Missing required option(s)");
     }
 
     [Fact]
-    public async Task Option_binding_fails_if_one_of_the_provided_option_names_is_not_recognized()
+    public async Task I_can_try_to_bind_options_and_get_an_error_if_the_user_provides_unrecognized_arguments()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -741,28 +730,30 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Unrecognized option(s)");
     }
 
     [Fact]
-    public async Task Option_binding_fails_if_an_option_of_scalar_type_has_been_provided_with_multiple_values()
+    public async Task I_can_try_to_bind_an_option_to_a_scalar_property_and_get_an_error_if_the_user_provides_too_many_arguments()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
-    [CommandOption(""foo"")]
-    public string Foo { get; set; }
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -775,10 +766,10 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("expects a single argument, but provided with multiple");
     }
 }

CliFx.Tests/ParameterBindingSpecs.cs

@@ -11,34 +11,34 @@ namespace CliFx.Tests;
 public class ParameterBindingSpecs : SpecsBase
 {
     public ParameterBindingSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Parameter_is_bound_from_an_argument_matching_its_order()
+    public async Task I_can_bind_a_parameter_to_a_property_and_get_the_value_from_the_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -51,49 +51,48 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = one",
-            "Bar = two"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = two");
     }
 
     [Fact]
-    public async Task Parameter_of_non_scalar_type_is_bound_from_remaining_non_option_arguments()
+    public async Task I_can_bind_a_parameter_to_a_non_scalar_property_and_get_values_from_the_remaining_non_option_arguments()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 [CommandParameter(2)]
-    public IReadOnlyList<string> Baz { get; set; }
+                public required IReadOnlyList<string> Baz { get; init; }
 
-    [CommandOption(""boo"")]
-    public string Boo { get; set; }
+                [CommandOption("boo")]
+                public string? Boo { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     foreach (var i in Baz)
-            console.Output.WriteLine(""Baz = "" + i);
+                        console.Output.WriteLine("Baz = " + i);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -106,43 +105,119 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = one",
-            "Bar = two",
-            "Baz = three",
-            "Baz = four",
-            "Baz = five"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ConsistOfLines("Foo = one", "Bar = two", "Baz = three", "Baz = four", "Baz = five");
     }
 
     [Fact]
-    public async Task Parameter_is_not_bound_if_there_are_no_arguments_matching_its_order()
+    public async Task I_can_try_to_bind_a_parameter_to_a_property_and_get_an_error_if_the_user_does_not_provide_the_corresponding_argument()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            new[] { "one" },
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required parameter(s)");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_to_a_non_scalar_property_and_get_an_error_if_the_user_does_not_provide_at_least_one_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required IReadOnlyList<string> Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            new[] { "one" },
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required parameter(s)");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_non_required_parameter_to_a_property_and_get_no_value_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
 
                 [CommandParameter(1, IsRequired = false)]
-    public string Bar { get; set; } = ""xyz"";
+                public string? Bar { get; init; } = "xyz";
 
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""Foo = "" + Foo);
-        console.Output.WriteLine(""Bar = "" + Bar);
+                    console.Output.WriteLine("Foo = " + Foo);
+                    console.Output.WriteLine("Bar = " + Bar);
 
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -155,109 +230,34 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
-        stdOut.Should().ConsistOfLines(
-            "Foo = abc",
-            "Bar = xyz"
-        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = abc", "Bar = xyz");
     }
 
     [Fact]
-    public async Task Parameter_binding_fails_if_a_required_parameter_has_not_been_provided()
+    public async Task I_can_try_to_bind_parameters_and_get_an_error_if_the_user_provides_too_many_arguments()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 [CommandParameter(0)]
-    public string Foo { get; set; }
+                public required string Foo { get; init; }
 
                 [CommandParameter(1)]
-    public string Bar { get; set; }
+                public required string Bar { get; init; }
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
-
-        var application = new CliApplicationBuilder()
-            .AddCommand(commandType)
-            .UseConsole(FakeConsole)
-            .Build();
-
-        // Act
-        var exitCode = await application.RunAsync(
-            new[] {"one"},
-            new Dictionary<string, string>()
-        );
-
-        var stdErr = FakeConsole.ReadErrorString();
-
-        // Assert
-        exitCode.Should().NotBe(0);
-        stdErr.Should().Contain("Missing required parameter(s)");
             }
-
-    [Fact]
-    public async Task Parameter_binding_fails_if_a_parameter_of_non_scalar_type_has_not_been_provided_with_at_least_one_value()
-    {
-        // Arrange
-        var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
-[Command]
-public class Command : ICommand
-{
-    [CommandParameter(0)]
-    public string Foo { get; set; }
-
-    [CommandParameter(1)]
-    public IReadOnlyList<string> Bar { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}");
-
-        var application = new CliApplicationBuilder()
-            .AddCommand(commandType)
-            .UseConsole(FakeConsole)
-            .Build();
-
-        // Act
-        var exitCode = await application.RunAsync(
-            new[] {"one"},
-            new Dictionary<string, string>()
+            """
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
-        // Assert
-        exitCode.Should().NotBe(0);
-        stdErr.Should().Contain("Missing required parameter(s)");
-    }
-
-    [Fact]
-    public async Task Parameter_binding_fails_if_one_of_the_provided_parameters_is_unexpected()
-    {
-        // Arrange
-        var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
-[Command]
-public class Command : ICommand
-{
-    [CommandParameter(0)]
-    public string Foo { get; set; }
-
-    [CommandParameter(1)]
-    public string Bar { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}");
-
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
             .UseConsole(FakeConsole)
@@ -269,10 +269,10 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Unexpected parameter(s)");
     }
 }

CliFx.Tests/RoutingSpecs.cs

@@ -11,47 +11,46 @@ namespace CliFx.Tests;
 public class RoutingSpecs : SpecsBase
 {
     public RoutingSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Default_command_is_executed_if_provided_arguments_do_not_match_any_named_command()
+    public async Task I_can_configure_a_command_to_be_executed_by_default_when_the_user_does_not_specify_a_command_name()
     {
         // Arrange
         var commandTypes = DynamicCommandBuilder.CompileMany(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class DefaultCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""default"");
+                    console.Output.WriteLine("default");
                     return default;
                 }
             }
 
-[Command(""cmd"")]
+            [Command("cmd")]
             public class NamedCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""cmd"");
+                    console.Output.WriteLine("cmd");
                     return default;
                 }
             }
 
-[Command(""cmd child"")]
+            [Command("cmd child")]
             public class NamedChildCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""cmd child"");
+                    console.Output.WriteLine("cmd child");
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommands(commandTypes)
@@ -64,50 +63,51 @@ public class NamedChildCommand : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("default");
     }
 
     [Fact]
-    public async Task Specific_named_command_is_executed_if_provided_arguments_match_its_name()
+    public async Task I_can_configure_a_command_to_be_executed_when_the_user_specifies_its_name()
     {
         // Arrange
         var commandTypes = DynamicCommandBuilder.CompileMany(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class DefaultCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""default"");
+                    console.Output.WriteLine("default");
                     return default;
                 }
             }
 
-[Command(""cmd"")]
+            [Command("cmd")]
             public class NamedCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""cmd"");
+                    console.Output.WriteLine("cmd");
                     return default;
                 }
             }
 
-[Command(""cmd child"")]
+            [Command("cmd child")]
             public class NamedChildCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""cmd child"");
+                    console.Output.WriteLine("cmd child");
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommands(commandTypes)
@@ -120,50 +120,51 @@ public class NamedChildCommand : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("cmd");
     }
 
     [Fact]
-    public async Task Specific_named_child_command_is_executed_if_provided_arguments_match_its_name()
+    public async Task I_can_configure_a_nested_command_to_be_executed_when_the_user_specifies_its_name()
     {
         // Arrange
         var commandTypes = DynamicCommandBuilder.CompileMany(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class DefaultCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""default"");
+                    console.Output.WriteLine("default");
                     return default;
                 }
             }
 
-[Command(""cmd"")]
+            [Command("cmd")]
             public class NamedCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""cmd"");
+                    console.Output.WriteLine("cmd");
                     return default;
                 }
             }
 
-[Command(""cmd child"")]
+            [Command("cmd child")]
             public class NamedChildCommand : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""cmd child"");
+                    console.Output.WriteLine("cmd child");
                     return default;
                 }
             }
-");
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommands(commandTypes)
@@ -176,10 +177,10 @@ public class NamedChildCommand : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("cmd child");
     }
 }

CliFx.Tests/SpecsBase.cs

@@ -11,8 +11,7 @@ public abstract class SpecsBase : IDisposable
 
     public FakeInMemoryConsole FakeConsole { get; } = new();
 
-    protected SpecsBase(ITestOutputHelper testOutput) =>
-        TestOutput = testOutput;
+    protected SpecsBase(ITestOutputHelper testOutput) => TestOutput = testOutput;
 
     public void Dispose()
     {

CliFx.Tests/TypeActivationSpecs.cs

@@ -13,26 +13,26 @@ namespace CliFx.Tests;
 public class TypeActivationSpecs : SpecsBase
 {
     public TypeActivationSpecs(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
+        : base(testOutput) { }
 
     [Fact]
-    public async Task Default_type_activator_can_initialize_a_type_if_it_has_a_parameterless_constructor()
+    public async Task I_can_configure_the_application_to_use_the_default_type_activator_to_initialize_types_through_parameterless_constructors()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""foo"");
+                    console.Output.WriteLine("foo");
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -46,27 +46,29 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("foo");
     }
 
     [Fact]
-    public async Task Default_type_activator_fails_if_the_type_does_not_have_a_parameterless_constructor()
+    public async Task I_can_try_to_configure_the_application_to_use_the_default_type_activator_and_get_an_error_if_the_requested_type_does_not_have_a_parameterless_constructor()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public Command(string foo) {}
 
                 public ValueTask ExecuteAsync(IConsole console) => default;
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -80,20 +82,20 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Failed to create an instance of type");
     }
 
     [Fact]
-    public async Task Custom_type_activator_can_initialize_a_type_using_a_given_function()
+    public async Task I_can_configure_the_application_to_use_a_custom_type_activator_to_initialize_types_using_a_delegate()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
@@ -106,7 +108,9 @@ public class Command : ICommand
                     console.Output.WriteLine(_foo);
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
@@ -120,20 +124,20 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("Hello world");
     }
 
     [Fact]
-    public async Task Custom_type_activator_can_initialize_a_type_using_a_service_provider()
+    public async Task I_can_configure_the_application_to_use_a_custom_type_activator_to_initialize_types_using_a_service_provider()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
@@ -146,16 +150,27 @@ public class Command : ICommand
                     console.Output.WriteLine(_foo);
                     return default;
                 }
-}");
-
-        var serviceProvider = new ServiceCollection()
-            .AddSingleton(commandType, Activator.CreateInstance(commandType, "Hello world")!)
-            .BuildServiceProvider();
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
             .UseConsole(FakeConsole)
-            .UseTypeActivator(serviceProvider)
+            .UseTypeActivator(commandTypes =>
+            {
+                var services = new ServiceCollection();
+
+                foreach (var serviceType in commandTypes)
+                {
+                    services.AddSingleton(
+                        serviceType,
+                        Activator.CreateInstance(serviceType, "Hello world")!
+                    );
+                }
+
+                return services.BuildServiceProvider();
+            })
             .Build();
 
         // Act
@@ -164,34 +179,36 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdOut = FakeConsole.ReadOutputString();
-
         // Assert
         exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
         stdOut.Trim().Should().Be("Hello world");
     }
 
     [Fact]
-    public async Task Custom_type_activator_fails_if_the_underlying_function_returns_null()
+    public async Task I_can_try_to_configure_the_application_to_use_a_custom_type_activator_and_get_an_error_if_the_requested_type_cannot_be_initialized()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
+            // lang=csharp
+            """
             [Command]
             public class Command : ICommand
             {
                 public ValueTask ExecuteAsync(IConsole console)
                 {
-        console.Output.WriteLine(""foo"");
+                    console.Output.WriteLine("foo");
                     return default;
                 }
-}");
+            }
+            """
+        );
 
         var application = new CliApplicationBuilder()
             .AddCommand(commandType)
             .UseConsole(FakeConsole)
-            .UseTypeActivator(_ => null!)
+            .UseTypeActivator((Type _) => null!)
             .Build();
 
         // Act
@@ -200,10 +217,10 @@ public class Command : ICommand
             new Dictionary<string, string>()
         );
 
-        var stdErr = FakeConsole.ReadErrorString();
-
         // Assert
         exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
         stdErr.Should().Contain("Failed to create an instance of type");
     }
 }

CliFx.Tests/Utils/DynamicCommandBuilder.cs

@@ -11,14 +11,9 @@ using Microsoft.CodeAnalysis.Text;
 namespace CliFx.Tests.Utils;
 
 // This class uses Roslyn to compile commands dynamically.
-//
-// It allows us to collocate commands with tests more
-// easily, which helps a lot when reasoning about them.
-// Unfortunately, this comes at a cost of static typing,
-// but this is still a worthwhile trade off.
-//
-// Maybe one day C# will allow declaring classes inside
-// methods and doing this will no longer be necessary.
+// It allows us to collocate commands with tests more easily, which helps a lot when reasoning about them.
+// Unfortunately, this comes at a cost of static typing, but this is still a worthwhile trade off.
+// Maybe one day C# will allow declaring classes inside methods and doing this will no longer be necessary.
 // Language proposal: https://github.com/dotnet/csharplang/discussions/130
 internal static class DynamicCommandBuilder
 {
@@ -46,10 +41,10 @@ internal static class DynamicCommandBuilder
 
         // Append default imports to the source code
         var sourceCodeWithUsings =
-            string.Join(Environment.NewLine, defaultSystemNamespaces.Select(n => $"using {n};")) +
-            string.Join(Environment.NewLine, defaultCliFxNamespaces.Select(n => $"using {n};")) +
-            Environment.NewLine +
-            sourceCode;
+            string.Join(Environment.NewLine, defaultSystemNamespaces.Select(n => $"using {n};"))
+            + string.Join(Environment.NewLine, defaultCliFxNamespaces.Select(n => $"using {n};"))
+            + Environment.NewLine
+            + sourceCode;
 
         // Parse the source code
         var ast = SyntaxFactory.ParseSyntaxTree(
@@ -61,9 +56,15 @@ internal static class DynamicCommandBuilder
         var compilation = CSharpCompilation.Create(
             "CliFxTests_DynamicAssembly_" + Guid.NewGuid(),
             new[] { ast },
-            ReferenceAssemblies.Net50
+            Net70
+                .References
+                .All
                 .Append(MetadataReference.CreateFromFile(typeof(ICommand).Assembly.Location))
-                .Append(MetadataReference.CreateFromFile(typeof(DynamicCommandBuilder).Assembly.Location)),
+                .Append(
+                    MetadataReference.CreateFromFile(
+                        typeof(DynamicCommandBuilder).Assembly.Location
+                    )
+                ),
             // DLL to avoid having to define the Main() method
             new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
         );
@@ -76,9 +77,10 @@ internal static class DynamicCommandBuilder
         if (compilationErrors.Any())
         {
             throw new InvalidOperationException(
-                "Failed to compile code." +
-                Environment.NewLine +
-                string.Join(Environment.NewLine, compilationErrors.Select(e => e.ToString()))
+                $"""
+                Failed to compile code.
+                {string.Join(Environment.NewLine, compilationErrors.Select(e => e.ToString()))}
+                """
             );
         }
 
@@ -86,17 +88,17 @@ internal static class DynamicCommandBuilder
         using var buffer = new MemoryStream();
         var emit = compilation.Emit(buffer);
 
-        var emitErrors = emit
-            .Diagnostics
+        var emitErrors = emit.Diagnostics
             .Where(d => d.Severity >= DiagnosticSeverity.Error)
             .ToArray();
 
         if (emitErrors.Any())
         {
             throw new InvalidOperationException(
-                "Failed to emit code." +
-                Environment.NewLine +
-                string.Join(Environment.NewLine, emitErrors.Select(e => e.ToString()))
+                $"""
+                Failed to emit code.
+                {string.Join(Environment.NewLine, emitErrors.Select(e => e.ToString()))}
+                """
             );
         }
 
@@ -122,7 +124,6 @@ internal static class DynamicCommandBuilder
     public static Type Compile(string sourceCode)
     {
         var commandTypes = CompileMany(sourceCode);
-
         if (commandTypes.Count > 1)
         {
             throw new InvalidOperationException(

CliFx.Tests/Utils/Extensions/AssertionExtensions.cs

@@ -10,20 +10,21 @@ internal static class AssertionExtensions
 {
     public static void ConsistOfLines(
         this StringAssertions assertions,
-        IEnumerable<string> lines)
-    {
-        var actualLines = assertions.Subject.Split(new[] {'\n', '\r'}, StringSplitOptions.RemoveEmptyEntries);
-        actualLines.Should().Equal(lines);
-    }
+        IEnumerable<string> lines
+    ) =>
+        assertions
+            .Subject
+            .Split(new[] { '\n', '\r' }, StringSplitOptions.RemoveEmptyEntries)
+            .Should()
+            .Equal(lines);
 
-    public static void ConsistOfLines(
-        this StringAssertions assertions,
-        params string[] lines) =>
+    public static void ConsistOfLines(this StringAssertions assertions, params string[] lines) =>
         assertions.ConsistOfLines((IEnumerable<string>)lines);
 
     public static AndConstraint<StringAssertions> ContainAllInOrder(
         this StringAssertions assertions,
-        IEnumerable<string> values)
+        IEnumerable<string> values
+    )
     {
         var lastIndex = 0;
 
@@ -33,7 +34,9 @@ internal static class AssertionExtensions
 
             if (index < 0)
             {
-                Execute.Assertion.FailWith(
+                Execute
+                    .Assertion
+                    .FailWith(
                         $"Expected string '{assertions.Subject}' to contain '{value}' after position {lastIndex}."
                     );
             }
@@ -41,11 +44,11 @@ internal static class AssertionExtensions
             lastIndex = index;
         }
 
-        return new(assertions);
+        return new AndConstraint<StringAssertions>(assertions);
     }
 
     public static AndConstraint<StringAssertions> ContainAllInOrder(
         this StringAssertions assertions,
-        params string[] values) =>
-        assertions.ContainAllInOrder((IEnumerable<string>) values);
+        params string[] values
+    ) => assertions.ContainAllInOrder((IEnumerable<string>)values);
 }

CliFx.Tests/Utils/Extensions/ConsoleExtensions.cs

@@ -5,12 +5,15 @@ namespace CliFx.Tests.Utils.Extensions;
 
 internal static class ConsoleExtensions
 {
-    public static void DumpToTestOutput(this FakeInMemoryConsole console, ITestOutputHelper testOutputHelper)
+    public static void DumpToTestOutput(
+        this FakeInMemoryConsole console,
+        ITestOutputHelper testOutput
+    )
     {
-        testOutputHelper.WriteLine("[*] Captured standard output:");
-        testOutputHelper.WriteLine(console.ReadOutputString());
+        testOutput.WriteLine("[*] Captured standard output:");
+        testOutput.WriteLine(console.ReadOutputString());
 
-        testOutputHelper.WriteLine("[*] Captured standard error:");
-        testOutputHelper.WriteLine(console.ReadErrorString());
+        testOutput.WriteLine("[*] Captured standard error:");
+        testOutput.WriteLine(console.ReadErrorString());
     }
 }

CliFx.Tests/Utils/NoOpCommand.cs

@@ -5,7 +5,7 @@ using CliFx.Infrastructure;
 namespace CliFx.Tests.Utils;
 
 [Command]
-public class NoOpCommand : ICommand
+internal class NoOpCommand : ICommand
 {
     public ValueTask ExecuteAsync(IConsole console) => default;
 }