Update version

Fixes #104

.gitattributes

@@ -1,63 +0,0 @@
-###############################################################################
-# Set default behavior to automatically normalize line endings.
-###############################################################################
-* text=auto
-
-###############################################################################
-# Set default behavior for command prompt diff.
-#
-# This is need for earlier builds of msysgit that does not have it on by
-# default for csharp files.
-# Note: This is only used by command line
-###############################################################################
-#*.cs     diff=csharp
-
-###############################################################################
-# Set the merge driver for project and solution files
-#
-# Merging from the command prompt will add diff markers to the files if there
-# are conflicts (Merging from VS is not affected by the settings below, in VS
-# the diff markers are never inserted). Diff markers may cause the following 
-# file extensions to fail to load in VS. An alternative would be to treat
-# these files as binary and thus will always conflict and require user
-# intervention with every merge. To do so, just uncomment the entries below
-###############################################################################
-#*.sln       merge=binary
-#*.csproj    merge=binary
-#*.vbproj    merge=binary
-#*.vcxproj   merge=binary
-#*.vcproj    merge=binary
-#*.dbproj    merge=binary
-#*.fsproj    merge=binary
-#*.lsproj    merge=binary
-#*.wixproj   merge=binary
-#*.modelproj merge=binary
-#*.sqlproj   merge=binary
-#*.wwaproj   merge=binary
-
-###############################################################################
-# behavior for image files
-#
-# image files are treated as binary by default.
-###############################################################################
-#*.jpg   binary
-#*.png   binary
-#*.gif   binary
-
-###############################################################################
-# diff behavior for common document formats
-# 
-# Convert binary document formats to text before diffing them. This feature
-# is only available from the command line. Turn it on by uncommenting the 
-# entries below.
-###############################################################################
-#*.doc   diff=astextplain
-#*.DOC   diff=astextplain
-#*.docx  diff=astextplain
-#*.DOCX  diff=astextplain
-#*.dot   diff=astextplain
-#*.DOT   diff=astextplain
-#*.pdf   diff=astextplain
-#*.PDF   diff=astextplain
-#*.rtf   diff=astextplain
-#*.RTF   diff=astextplain

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -0,0 +1,30 @@
+name: "\U0001F41E Bug report"
+description: Report broken functionality.
+labels: [bug]
+body:
+- type: markdown
+  attributes:
+    value: |
+      - Please check existing issues (both opened and closed) to ensure that this bug hasn't been reported before.
+      - If you want to ask a question instead of reporting a bug, use [discussions](https://github.com/Tyrrrz/CliFx/discussions/new) instead.
+
+- type: input
+  attributes:
+    label: Version
+    description: "Which version(s) of CliFx does this bug affect?"
+  validations:
+    required: true
+
+- type: textarea
+  attributes:
+    label: Details
+    description: "Clear and thorough explanation of the bug. If relevant, include screenshots or screen recordings."
+  validations:
+    required: true
+
+- type: textarea
+  attributes:
+    label: Steps to reproduce
+    description: "Minimum steps or code required to reproduce the bug."
+  validations:
+    required: true

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: false
+contact_links:
+  - name: "\U0001F5E8 Ask a question"
+    url: https://github.com/Tyrrrz/CliFx/discussions/new
+    about: Please ask and answer questions here.  

.github/ISSUE_TEMPLATE/feature-request.yml

@@ -0,0 +1,16 @@
+name: "\U00002728 Feature request"
+description: Request a new feature.
+labels: [enhancement]
+body:
+- type: markdown
+  attributes:
+    value: |
+      - Please check existing issues (both opened and closed) to ensure that this feature hasn't been requested before.
+      - If you want to ask a question instead of requesting a feature, 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/CD.yml

@@ -3,7 +3,7 @@ name: CD
 on:
   push:
     tags:
-    - '*'
+      - "*"
 
 jobs:
   build:
@@ -11,12 +11,12 @@ jobs:
 
     steps:
       - name: Checkout
-      uses: actions/checkout@v2
+        uses: actions/checkout@v2.3.3
 
-    - name: Install .NET Core
+      - name: Install .NET
-      uses: actions/setup-dotnet@v1.4.0
+        uses: actions/setup-dotnet@v1.7.2
         with:
-        dotnet-version: 3.1.100
+          dotnet-version: 5.0.x
 
       - name: Pack
         run: dotnet pack CliFx --configuration Release

.github/workflows/CI.yml

@@ -12,12 +12,12 @@ jobs:
 
     steps:
       - name: Checkout
-      uses: actions/checkout@v2
+        uses: actions/checkout@v2.3.3
 
-    - name: Install .NET Core
+      - name: Install .NET
-      uses: actions/setup-dotnet@v1.4.0
+        uses: actions/setup-dotnet@v1.7.2
         with:
-        dotnet-version: 3.1.100
+          dotnet-version: 5.0.x
 
       - name: Build & test
         run: dotnet test --configuration Release --logger GitHubActions
@@ -26,10 +26,3 @@ jobs:
         uses: codecov/codecov-action@v1.0.5
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
-        file: CliFx.Tests/bin/Release/Coverage.xml
-
-    - name: Upload coverage (analyzers)
-      uses: codecov/codecov-action@v1.0.5
-      with:
-        token: ${{ secrets.CODECOV_TOKEN }}
-        file: CliFx.Analyzers.Tests/bin/Release/Coverage.xml

.gitignore

@@ -1,341 +1,21 @@
-## Ignore Visual Studio temporary files, build results, and
-## files generated by popular Visual Studio add-ons.
-##
-## Get latest from https://github.com/github/gitignore/blob/master/VisualStudio.gitignore
-
 # User-specific files
-*.rsuser
 *.suo
 *.user
 *.userosscache
 *.sln.docstates
-
+.idea/
-# User-specific files (MonoDevelop/Xamarin Studio)
-*.userprefs
 
 # Build results
 [Dd]ebug/
 [Dd]ebugPublic/
 [Rr]elease/
 [Rr]eleases/
-x64/
+[Xx]64/
-x86/
+[Xx]86/
-[Aa][Rr][Mm]/
+[Bb]uild/
-[Aa][Rr][Mm]64/
 bld/
 [Bb]in/
 [Oo]bj/
-[Ll]og/
 
-# Visual Studio 2015/2017 cache/options directory
+# Coverage
-.vs/
+*.opencover.xml
-# Uncomment if you have tasks that create the project's static files in wwwroot
-#wwwroot/
-
-# Visual Studio 2017 auto generated files
-Generated\ Files/
-
-# MSTest test Results
-[Tt]est[Rr]esult*/
-[Bb]uild[Ll]og.*
-
-# NUNIT
-*.VisualState.xml
-TestResult.xml
-
-# Build Results of an ATL Project
-[Dd]ebugPS/
-[Rr]eleasePS/
-dlldata.c
-
-# Benchmark Results
-BenchmarkDotNet.Artifacts/
-
-# .NET Core
-project.lock.json
-project.fragment.lock.json
-artifacts/
-
-# StyleCop
-StyleCopReport.xml
-
-# Files built by Visual Studio
-*_i.c
-*_p.c
-*_h.h
-*.ilk
-*.meta
-*.obj
-*.iobj
-*.pch
-*.pdb
-*.ipdb
-*.pgc
-*.pgd
-*.rsp
-*.sbr
-*.tlb
-*.tli
-*.tlh
-*.tmp
-*.tmp_proj
-*_wpftmp.csproj
-*.log
-*.vspscc
-*.vssscc
-.builds
-*.pidb
-*.svclog
-*.scc
-
-# Chutzpah Test files
-_Chutzpah*
-
-# Visual C++ cache files
-ipch/
-*.aps
-*.ncb
-*.opendb
-*.opensdf
-*.sdf
-*.cachefile
-*.VC.db
-*.VC.VC.opendb
-
-# Visual Studio profiler
-*.psess
-*.vsp
-*.vspx
-*.sap
-
-# Visual Studio Trace Files
-*.e2e
-
-# TFS 2012 Local Workspace
-$tf/
-
-# Guidance Automation Toolkit
-*.gpState
-
-# ReSharper is a .NET coding add-in
-_ReSharper*/
-*.[Rr]e[Ss]harper
-*.DotSettings.user
-
-# JustCode is a .NET coding add-in
-.JustCode
-
-# TeamCity is a build add-in
-_TeamCity*
-
-# DotCover is a Code Coverage Tool
-*.dotCover
-
-# AxoCover is a Code Coverage Tool
-.axoCover/*
-!.axoCover/settings.json
-
-# Visual Studio code coverage results
-*.coverage
-*.coveragexml
-
-# NCrunch
-_NCrunch_*
-.*crunch*.local.xml
-nCrunchTemp_*
-.ncrunchsolution
-
-# MightyMoose
-*.mm.*
-AutoTest.Net/
-
-# Web workbench (sass)
-.sass-cache/
-
-# Installshield output folder
-[Ee]xpress/
-
-# DocProject is a documentation generator add-in
-DocProject/buildhelp/
-DocProject/Help/*.HxT
-DocProject/Help/*.HxC
-DocProject/Help/*.hhc
-DocProject/Help/*.hhk
-DocProject/Help/*.hhp
-DocProject/Help/Html2
-DocProject/Help/html
-
-# Click-Once directory
-publish/
-
-# Publish Web Output
-*.[Pp]ublish.xml
-*.azurePubxml
-# Note: Comment the next line if you want to checkin your web deploy settings,
-# but database connection strings (with potential passwords) will be unencrypted
-*.pubxml
-*.publishproj
-
-# Microsoft Azure Web App publish settings. Comment the next line if you want to
-# checkin your Azure Web App publish settings, but sensitive information contained
-# in these scripts will be unencrypted
-PublishScripts/
-
-# NuGet Packages
-*.nupkg
-# The packages folder can be ignored because of Package Restore
-**/[Pp]ackages/*
-# except build/, which is used as an MSBuild target.
-!**/[Pp]ackages/build/
-# Uncomment if necessary however generally it will be regenerated when needed
-#!**/[Pp]ackages/repositories.config
-# NuGet v3's project.json files produces more ignorable files
-*.nuget.props
-*.nuget.targets
-
-# Microsoft Azure Build Output
-csx/
-*.build.csdef
-
-# Microsoft Azure Emulator
-ecf/
-rcf/
-
-# Windows Store app package directories and files
-AppPackages/
-BundleArtifacts/
-Package.StoreAssociation.xml
-_pkginfo.txt
-*.appx
-
-# Visual Studio cache files
-# files ending in .cache can be ignored
-*.[Cc]ache
-# but keep track of directories ending in .cache
-!?*.[Cc]ache/
-
-# Others
-ClientBin/
-~$*
-*~
-*.dbmdl
-*.dbproj.schemaview
-*.jfm
-*.pfx
-*.publishsettings
-orleans.codegen.cs
-
-# Including strong name files can present a security risk
-# (https://github.com/github/gitignore/pull/2483#issue-259490424)
-#*.snk
-
-# Since there are multiple workflows, uncomment next line to ignore bower_components
-# (https://github.com/github/gitignore/pull/1529#issuecomment-104372622)
-#bower_components/
-
-# RIA/Silverlight projects
-Generated_Code/
-
-# Backup & report files from converting an old project file
-# to a newer Visual Studio version. Backup files are not needed,
-# because we have git ;-)
-_UpgradeReport_Files/
-Backup*/
-UpgradeLog*.XML
-UpgradeLog*.htm
-ServiceFabricBackup/
-*.rptproj.bak
-
-# SQL Server files
-*.mdf
-*.ldf
-*.ndf
-
-# Business Intelligence projects
-*.rdl.data
-*.bim.layout
-*.bim_*.settings
-*.rptproj.rsuser
-*- Backup*.rdl
-
-# Microsoft Fakes
-FakesAssemblies/
-
-# GhostDoc plugin setting file
-*.GhostDoc.xml
-
-# Node.js Tools for Visual Studio
-.ntvs_analysis.dat
-node_modules/
-
-# Visual Studio 6 build log
-*.plg
-
-# Visual Studio 6 workspace options file
-*.opt
-
-# Visual Studio 6 auto-generated workspace file (contains which files were open etc.)
-*.vbw
-
-# Visual Studio LightSwitch build output
-**/*.HTMLClient/GeneratedArtifacts
-**/*.DesktopClient/GeneratedArtifacts
-**/*.DesktopClient/ModelManifest.xml
-**/*.Server/GeneratedArtifacts
-**/*.Server/ModelManifest.xml
-_Pvt_Extensions
-
-# Paket dependency manager
-.paket/paket.exe
-paket-files/
-
-# FAKE - F# Make
-.fake/
-
-# JetBrains Rider
-.idea/
-*.sln.iml
-
-# CodeRush personal settings
-.cr/personal
-
-# Python Tools for Visual Studio (PTVS)
-__pycache__/
-*.pyc
-
-# Cake - Uncomment if you are using it
-# tools/**
-# !tools/packages.config
-
-# Tabs Studio
-*.tss
-
-# Telerik's JustMock configuration file
-*.jmconfig
-
-# BizTalk build output
-*.btp.cs
-*.btm.cs
-*.odx.cs
-*.xsd.cs
-
-# OpenCover UI analysis results
-OpenCover/
-
-# Azure Stream Analytics local run output
-ASALocalRun/
-
-# MSBuild Binary and Structured Log
-*.binlog
-
-# NVidia Nsight GPU debugger configuration file
-*.nvuser
-
-# MFractors (Xamarin productivity tool) working folder
-.mfractor/
-
-# Local History for Visual Studio
-.localhistory/
-
-# BeatPulse healthcheck temp database
-healthchecksdb

Changelog.md

@@ -1,3 +1,85 @@
+### 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)
+
+- 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)
+
+- 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)
+
+- 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)
+
+> Note: this major release includes many breaking changes.
+Please refer to the readme to find updated instructions and usage examples.
+
+- Renamed property `EnvironmentVariableName` to `EnvironmentVariable` on `CommandOption` attribute.
+- Removed most of schema validation checks that used to take place during application startup. Going forward, CliFx will be relying solely on its built-in set of Roslyn analyzers to catch common errors in command configuration.
+- Removed `ProgressTicker` utility. The recommended migration path is to use the [Spectre.Console](https://github.com/spectresystems/spectre.console) library which provides a wide array of console widgets and components. See [this wiki page](https://github.com/Tyrrrz/CliFx/wiki/Integrating-with-Spectre.Console) to learn how to integrate Spectre.Console with CliFx.
+- Removed `MemoryStreamWriter` utility as it's no longer used within CliFx.
+- Improved wording in all error messages.
+- Renamed some methods on `CliApplicationBuilder`:
+  - `UseTitle()` renamed to `SetTitle()`
+  - `UseExecutableName()` renamed to `SetExecutableName()`
+  - `UseVersionText()` renamed to `SetVersion()`
+  - `UseDescription()` renamed to `SetDescription()`
+- Changed the behavior of autogenerated help text:
+  - Changed the color scheme to a more neutral set of tones
+  - 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.
+- 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.
+- Changed the type of `IConsole.Input` from `StreamReader` to `ConsoleReader`. This type derives from `StreamReader` 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 the console input stream.
+- Changed methods `IConsole.WithForegroundColor(...)`, `IConsole.WithBackgroundColor(...)`, and `IConsole.WithColors(...)` to return `IDisposable`, replacing the delegate parameter they previously had. You can wrap the returned `IDisposable` in a using statement to ensure that the console colors get reset back to their original values once the execution reaches the end of the block.
+- Renamed `IConsole.GetCancellationToken()` to `IConsole.RegisterCancellationHandler()`.
+- Reworked `VirtualConsole` into `FakeConsole`. This class no longer takes `CancellationToken` as a constructor parameter, but instead encapsulates its own instance of `CancellationTokenSource` that can be triggered using the provided `RequestCancellation()` method.
+- Removed `VirtualConsole.CreateBuffered()` and replaced it with the `FakeInMemoryConsole` class. This class derives from `FakeConsole` and uses in-memory standard input, output, and error streams. It also provides methods to easily read the data written to the streams.
+- Moved some types to different namespaces:
+  - `IConsole`/`FakeConsole`/`FakeInMemoryConsole` moved from `CliFx` to `CliFx.Infrastructure`
+  - `ITypeActivator`/`DefaultTypeActivator`/`DelegateTypeActivator` moved from `CliFx` to `CliFx.Infrastructure`
+  - `BindingValidator`/`BindingConverter` moved from `CliFx` to `CliFx.Extensibility`
+
+### 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)
+
+- 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)
+
+- 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)
+
+- 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)
+
+- 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)
 
 - 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.

CliFx.Analyzers.Tests/AnalyzerTestCase.cs

@@ -1,43 +0,0 @@
-using System.Collections.Generic;
-using System.Linq;
-using Microsoft.CodeAnalysis;
-
-namespace CliFx.Analyzers.Tests
-{
-    public class AnalyzerTestCase
-    {
-        public string Name { get; }
-
-        public IReadOnlyList<DiagnosticDescriptor> TestedDiagnostics { get; }
-
-        public IReadOnlyList<string> SourceCodes { get; }
-
-        public AnalyzerTestCase(
-            string name,
-            IReadOnlyList<DiagnosticDescriptor> testedDiagnostics,
-            IReadOnlyList<string> sourceCodes)
-        {
-            Name = name;
-            TestedDiagnostics = testedDiagnostics;
-            SourceCodes = sourceCodes;
-        }
-
-        public AnalyzerTestCase(
-            string name,
-            IReadOnlyList<DiagnosticDescriptor> testedDiagnostics,
-            string sourceCode)
-            : this(name, testedDiagnostics, new[] {sourceCode})
-        {
-        }
-
-        public AnalyzerTestCase(
-            string name,
-            DiagnosticDescriptor testedDiagnostic,
-            string sourceCode)
-            : this(name, new[] {testedDiagnostic}, sourceCode)
-        {
-        }
-
-        public override string ToString() => $"{Name} [{string.Join(", ", TestedDiagnostics.Select(d => d.Id))}]";
-    }
-}

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

@@ -1,24 +1,25 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
     <CollectCoverage>true</CollectCoverage>
     <CoverletOutputFormat>opencover</CoverletOutputFormat>
-    <CoverletOutput>bin/$(Configuration)/Coverage.xml</CoverletOutput>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Gu.Roslyn.Asserts" Version="3.3.0" />
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
-    <PackageReference Include="GitHubActionsTestLogger" Version="1.0.0" />
+  </ItemGroup>
-    <PackageReference Include="FluentAssertions" Version="5.10.2" />
+
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
+  <ItemGroup>
+    <PackageReference Include="GitHubActionsTestLogger" Version="1.2.0" />
+    <PackageReference Include="FluentAssertions" Version="5.10.3" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.4" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.4.0" />
     <PackageReference Include="xunit" Version="2.4.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="3.4.0" />
+    <PackageReference Include="coverlet.msbuild" Version="3.0.3" PrivateAssets="all" />
-    <PackageReference Include="coverlet.msbuild" Version="2.8.0" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Analyzers.Tests/CommandMustBeAnnotatedAnalyzerSpecs.cs

@@ -0,0 +1,72 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class CommandMustBeAnnotatedAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new CommandMustBeAnnotatedAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_a_command_is_not_annotated_with_the_command_attribute()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_command_is_annotated_with_the_command_attribute()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public abstract class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_command_is_implemented_as_an_abstract_class()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public abstract class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_on_a_class_that_is_not_a_command()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class Foo
+{
+    public int Bar { get; set; } = 5;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/CommandMustImplementInterfaceAnalyzerSpecs.cs

@@ -0,0 +1,58 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class CommandMustImplementInterfaceAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand
+{
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_command_implements_ICommand_interface()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_on_a_class_that_is_not_a_command()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class Foo
+{
+    public int Bar { get; set; } = 5;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/CommandSchemaAnalyzerTests.cs

@@ -1,489 +0,0 @@
-using System.Collections.Generic;
-using CliFx.Analyzers.Tests.Internal;
-using Microsoft.CodeAnalysis.Diagnostics;
-using Xunit;
-
-namespace CliFx.Analyzers.Tests
-{
-    public class CommandSchemaAnalyzerTests
-    {
-        private static DiagnosticAnalyzer Analyzer { get; } = new CommandSchemaAnalyzer();
-
-        public static IEnumerable<object[]> GetValidCases()
-        {
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Non-command type",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-public class Foo
-{
-    public int Bar { get; set; } = 5;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Command implements interface and has attribute",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Command doesn't have an attribute but is an abstract type",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-public abstract class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Parameters with unique order",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(13)]
-    public string ParamA { get; set; }
-    
-    [CommandParameter(15)]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Parameters with unique names",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(13, Name = ""foo"")]
-    public string ParamA { get; set; }
-    
-    [CommandParameter(15, Name = ""bar"")]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Single non-scalar parameter",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(1)]
-    public string ParamA { get; set; }
-    
-    [CommandParameter(2)]
-    public HashSet<string> ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Non-scalar parameter is last in order",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(1)]
-    public string ParamA { get; set; }
-    
-    [CommandParameter(2)]
-    public IReadOnlyList<string> ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Option with a proper name",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption(""foo"")]
-    public string Param { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Option with a proper name and short name",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption(""foo"", 'f')]
-    public string Param { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Options with unique names",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption(""foo"")]
-    public string ParamA { get; set; }
-    
-    [CommandOption(""bar"")]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Options with unique short names",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption('f')]
-    public string ParamA { get; set; }
-    
-    [CommandOption('x')]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Options with unique environment variable names",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption('a', EnvironmentVariableName = ""env_var_a"")]
-    public string ParamA { get; set; }
-    
-    [CommandOption('b', EnvironmentVariableName = ""env_var_b"")]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-        }
-
-        public static IEnumerable<object[]> GetInvalidCases()
-        {
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Command is missing the attribute",
-                    DiagnosticDescriptors.CliFx0002,
-
-                    // language=cs
-                    @"
-public class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Command doesn't implement the interface",
-                    DiagnosticDescriptors.CliFx0001,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand
-{
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Parameters with duplicate order",
-                    DiagnosticDescriptors.CliFx0021,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(13)]
-    public string ParamA { get; set; }
-    
-    [CommandParameter(13)]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Parameters with duplicate names",
-                    DiagnosticDescriptors.CliFx0022,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(13, Name = ""foo"")]
-    public string ParamA { get; set; }
-    
-    [CommandParameter(15, Name = ""foo"")]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Multiple non-scalar parameters",
-                    DiagnosticDescriptors.CliFx0023,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(1)]
-    public IReadOnlyList<string> ParamA { get; set; }
-    
-    [CommandParameter(2)]
-    public HashSet<string> ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Non-last non-scalar parameter",
-                    DiagnosticDescriptors.CliFx0024,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandParameter(1)]
-    public IReadOnlyList<string> ParamA { get; set; }
-    
-    [CommandParameter(2)]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Option with an empty name",
-                    DiagnosticDescriptors.CliFx0041,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption("""")]
-    public string Param { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Option with a name which is too short",
-                    DiagnosticDescriptors.CliFx0042,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption(""a"")]
-    public string Param { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Options with duplicate names",
-                    DiagnosticDescriptors.CliFx0043,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption(""foo"")]
-    public string ParamA { get; set; }
-    
-    [CommandOption(""foo"")]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Options with duplicate short names",
-                    DiagnosticDescriptors.CliFx0044,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption('f')]
-    public string ParamA { get; set; }
-    
-    [CommandOption('f')]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Options with duplicate environment variable names",
-                    DiagnosticDescriptors.CliFx0045,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    [CommandOption('a', EnvironmentVariableName = ""env_var"")]
-    public string ParamA { get; set; }
-    
-    [CommandOption('b', EnvironmentVariableName = ""env_var"")]
-    public string ParamB { get; set; }
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-        }
-
-        [Theory]
-        [MemberData(nameof(GetValidCases))]
-        public void Valid(AnalyzerTestCase testCase) =>
-            Analyzer.Should().NotProduceDiagnostics(testCase);
-
-        [Theory]
-        [MemberData(nameof(GetInvalidCases))]
-        public void Invalid(AnalyzerTestCase testCase) =>
-            Analyzer.Should().ProduceDiagnostics(testCase);
-    }
-}

CliFx.Analyzers.Tests/ConsoleUsageAnalyzerTests.cs

@@ -1,144 +0,0 @@
-using System.Collections.Generic;
-using CliFx.Analyzers.Tests.Internal;
-using Microsoft.CodeAnalysis.Diagnostics;
-using Xunit;
-
-namespace CliFx.Analyzers.Tests
-{
-    public class ConsoleUsageAnalyzerTests
-    {
-        private static DiagnosticAnalyzer Analyzer { get; } = new ConsoleUsageAnalyzer();
-
-        public static IEnumerable<object[]> GetValidCases()
-        {
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Using console abstraction",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console)
-    {
-        console.Output.WriteLine(""Hello world"");
-        return default;
-    }
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Console abstraction is not available in scope",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public void SomeOtherMethod() => Console.WriteLine(""Test"");
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-        }
-
-        public static IEnumerable<object[]> GetInvalidCases()
-        {
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Not using available console abstraction in the ExecuteAsync method",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console)
-    {
-        Console.WriteLine(""Hello world"");
-        return default;
-    }
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Not using available console abstraction in the ExecuteAsync method when writing stderr",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console)
-    {
-        Console.Error.WriteLine(""Hello world"");
-        return default;
-    }
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Not using available console abstraction while referencing System.Console by full name",
-                    Analyzer.SupportedDiagnostics,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public ValueTask ExecuteAsync(IConsole console)
-    {
-        System.Console.Error.WriteLine(""Hello world"");
-        return default;
-    }
-}"
-                )
-            };
-
-            yield return new object[]
-            {
-                new AnalyzerTestCase(
-                    "Not using available console abstraction in another method",
-                    DiagnosticDescriptors.CliFx0100,
-
-                    // language=cs
-                    @"
-[Command]
-public class MyCommand : ICommand
-{
-    public void SomeOtherMethod(IConsole console) => Console.WriteLine(""Test"");
-
-    public ValueTask ExecuteAsync(IConsole console) => default;
-}"
-                )
-            };
-        }
-
-        [Theory]
-        [MemberData(nameof(GetValidCases))]
-        public void Valid(AnalyzerTestCase testCase) =>
-            Analyzer.Should().NotProduceDiagnostics(testCase);
-
-        [Theory]
-        [MemberData(nameof(GetInvalidCases))]
-        public void Invalid(AnalyzerTestCase testCase) =>
-            Analyzer.Should().ProduceDiagnostics(testCase);
-    }
-}

CliFx.Analyzers.Tests/GeneralSpecs.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Linq;
+using FluentAssertions;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class GeneralSpecs
+    {
+        [Fact]
+        public void All_analyzers_have_unique_diagnostic_IDs()
+        {
+            // Arrange
+            var analyzers = typeof(AnalyzerBase)
+                .Assembly
+                .GetTypes()
+                .Where(t => !t.IsAbstract && t.IsAssignableTo(typeof(DiagnosticAnalyzer)))
+                .Select(t => (DiagnosticAnalyzer) Activator.CreateInstance(t)!)
+                .ToArray();
+
+            // Act
+            var diagnosticIds = analyzers
+                .SelectMany(a => a.SupportedDiagnostics.Select(d => d.Id))
+                .ToArray();
+
+            // Assert
+            diagnosticIds.Should().OnlyHaveUniqueItems();
+        }
+    }
+}

CliFx.Analyzers.Tests/Internal/AnalyzerAssertions.cs

@@ -1,107 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using FluentAssertions.Execution;
-using FluentAssertions.Primitives;
-using Gu.Roslyn.Asserts;
-using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.CSharp;
-using Microsoft.CodeAnalysis.Diagnostics;
-
-namespace CliFx.Analyzers.Tests.Internal
-{
-    internal partial class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer, AnalyzerAssertions>
-    {
-        protected override string Identifier { get; } = "analyzer";
-
-        public AnalyzerAssertions(DiagnosticAnalyzer analyzer)
-            : base(analyzer)
-        {
-        }
-
-        public void ProduceDiagnostics(
-            IReadOnlyList<DiagnosticDescriptor> diagnostics,
-            IReadOnlyList<string> sourceCodes)
-        {
-            var producedDiagnostics = GetProducedDiagnostics(Subject, sourceCodes);
-
-            var expectedIds = diagnostics.Select(d => d.Id).Distinct().OrderBy(d => d).ToArray();
-            var producedIds = producedDiagnostics.Select(d => d.Id).Distinct().OrderBy(d => d).ToArray();
-
-            var result = expectedIds.Intersect(producedIds).Count() == expectedIds.Length;
-
-            Execute.Assertion.ForCondition(result).FailWith($@"
-Expected and produced diagnostics do not match.
-
-Expected: {string.Join(", ", expectedIds)}
-Produced: {(producedIds.Any() ? string.Join(", ", producedIds) : "<none>")}
-".Trim());
-        }
-
-        public void ProduceDiagnostics(AnalyzerTestCase testCase) =>
-            ProduceDiagnostics(testCase.TestedDiagnostics, testCase.SourceCodes);
-
-        public void NotProduceDiagnostics(
-            IReadOnlyList<DiagnosticDescriptor> diagnostics,
-            IReadOnlyList<string> sourceCodes)
-        {
-            var producedDiagnostics = GetProducedDiagnostics(Subject, sourceCodes);
-
-            var expectedIds = diagnostics.Select(d => d.Id).Distinct().OrderBy(d => d).ToArray();
-            var producedIds = producedDiagnostics.Select(d => d.Id).Distinct().OrderBy(d => d).ToArray();
-
-            var result = !expectedIds.Intersect(producedIds).Any();
-
-            Execute.Assertion.ForCondition(result).FailWith($@"
-Expected no produced diagnostics.
-
-Produced: {string.Join(", ", producedIds)}
-".Trim());
-        }
-
-        public void NotProduceDiagnostics(AnalyzerTestCase testCase) =>
-            NotProduceDiagnostics(testCase.TestedDiagnostics, testCase.SourceCodes);
-    }
-
-    internal partial class AnalyzerAssertions
-    {
-        private static IReadOnlyList<MetadataReference> DefaultMetadataReferences { get; } =
-            MetadataReferences.Transitive(typeof(CliApplication).Assembly).ToArray();
-
-        private static string WrapCodeWithUsingDirectives(string code)
-        {
-            var usingDirectives = new[]
-            {
-                "using System;",
-                "using System.Collections.Generic;",
-                "using System.Threading.Tasks;",
-                "using CliFx;",
-                "using CliFx.Attributes;",
-                "using CliFx.Exceptions;",
-                "using CliFx.Utilities;"
-            };
-
-            return
-                string.Join(Environment.NewLine, usingDirectives) +
-                Environment.NewLine +
-                code;
-        }
-
-        private static IReadOnlyList<Diagnostic> GetProducedDiagnostics(
-            DiagnosticAnalyzer analyzer,
-            IReadOnlyList<string> sourceCodes)
-        {
-            var compilationOptions = new CSharpCompilationOptions(OutputKind.ConsoleApplication);
-            var wrappedSourceCodes = sourceCodes.Select(WrapCodeWithUsingDirectives).ToArray();
-
-            return Analyze.GetDiagnostics(analyzer, wrappedSourceCodes, compilationOptions, DefaultMetadataReferences)
-                .SelectMany(d => d)
-                .ToArray();
-        }
-    }
-
-    internal static class AnalyzerAssertionsExtensions
-    {
-        public static AnalyzerAssertions Should(this DiagnosticAnalyzer analyzer) => new AnalyzerAssertions(analyzer);
-    }
-}

CliFx.Analyzers.Tests/OptionMustBeInsideCommandAnalyzerSpecs.cs

@@ -0,0 +1,80 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustBeInsideCommandAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustBeInsideCommandAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_an_option_is_inside_a_class_that_is_not_a_command()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyClass
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_is_inside_a_command()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_is_inside_an_abstract_class()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public abstract class MyCommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_an_option()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveNameOrShortNameAnalyzerSpecs.cs

@@ -0,0 +1,86 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveNameOrShortNameAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(null)]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_has_a_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_has_a_short_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveUniqueNameAnalyzerSpecs.cs

@@ -0,0 +1,92 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveUniqueNameAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveUniqueNameAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_an_option_has_the_same_name_as_another_option()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    [CommandOption(""foo"")]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_has_a_unique_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    [CommandOption(""bar"")]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveUniqueShortNameAnalyzerSpecs.cs

@@ -0,0 +1,114 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveUniqueShortNameAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    [CommandOption('f')]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_has_a_unique_short_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    [CommandOption('b')]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    [CommandOption('F')]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_short_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveValidConverterAnalyzerSpecs.cs

@@ -0,0 +1,96 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveValidConverterAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveValidConverterAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_the_specified_option_converter_does_not_derive_from_BindingConverter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyConverter
+{
+    public string Convert(string rawValue) => rawValue;
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"", Converter = typeof(MyConverter))]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_the_specified_option_converter_derives_from_BindingConverter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyConverter : BindingConverter<string>
+{
+    public override string Convert(string rawValue) => rawValue;
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"", Converter = typeof(MyConverter))]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_converter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveValidNameAnalyzerSpecs.cs

@@ -0,0 +1,105 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveValidNameAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveValidNameAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_an_option_has_a_name_which_is_too_short()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""f"")]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""1foo"")]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_has_a_valid_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveValidShortNameAnalyzerSpecs.cs

@@ -0,0 +1,86 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveValidShortNameAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('1')]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_has_a_valid_short_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption('f')]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_a_short_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/OptionMustHaveValidValidatorsAnalyzerSpecs.cs

@@ -0,0 +1,96 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class OptionMustHaveValidValidatorsAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new OptionMustHaveValidValidatorsAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_one_of_the_specified_option_validators_does_not_derive_from_BindingValidator()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyValidator
+{
+    public void Validate(string value) {}
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"", Validators = new[] {typeof(MyValidator)})]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_all_specified_option_validators_derive_from_BindingValidator()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyValidator : BindingValidator<string>
+{
+    public override BindingValidationError Validate(string value) => Ok();
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"", Validators = new[] {typeof(MyValidator)})]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_an_option_does_not_have_validators()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandOption(""foo"")]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustBeInsideCommandAnalyzerSpecs.cs

@@ -0,0 +1,80 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustBeInsideCommandAnalyzerSpecs
+    {
+        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 = @"
+public class MyClass
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_parameter_is_inside_a_command()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_parameter_is_inside_an_abstract_class()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public abstract class MyCommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_on_a_property_that_is_not_a_parameter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustBeLastIfNonScalarAnalyzerSpecs.cs

@@ -0,0 +1,95 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustBeLastIfNonScalarAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeLastIfNonScalarAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_a_non_scalar_parameter_is_not_last_in_order()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string[] Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_non_scalar_parameter_is_last_in_order()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string[] Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_no_non_scalar_parameters_are_defined()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string Bar { get; set; }
+
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustBeSingleIfNonScalarAnalyzerSpecs.cs

@@ -0,0 +1,95 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustBeSingleIfNonScalarAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string[] Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string[] Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_only_one_non_scalar_parameter_is_defined()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string[] Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_no_non_scalar_parameters_are_defined()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string Bar { get; set; }
+
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustHaveUniqueNameAnalyzerSpecs.cs

@@ -0,0 +1,73 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustHaveUniqueNameAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustHaveUniqueNameAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_a_parameter_has_the_same_name_as_another_parameter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"")]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1, Name = ""foo"")]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_parameter_has_unique_name()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"")]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1, Name = ""bar"")]
+    public string Bar { get; set; }
+
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustHaveUniqueOrderAnalyzerSpecs.cs

@@ -0,0 +1,73 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustHaveUniqueOrderAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    [CommandParameter(0)]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_parameter_has_unique_order()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1)]
+    public string Bar { get; set; }
+
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustHaveValidConverterAnalyzerSpecs.cs

@@ -0,0 +1,96 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustHaveValidConverterAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustHaveValidConverterAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_the_specified_parameter_converter_does_not_derive_from_BindingConverter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyConverter
+{
+    public string Convert(string rawValue) => rawValue;
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Converter = typeof(MyConverter))]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_the_specified_parameter_converter_derives_from_BindingConverter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyConverter : BindingConverter<string>
+{
+    public override string Convert(string rawValue) => rawValue;
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Converter = typeof(MyConverter))]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_parameter_does_not_have_a_converter()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/ParameterMustHaveValidValidatorsAnalyzerSpecs.cs

@@ -0,0 +1,96 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class ParameterMustHaveValidValidatorsAnalyzerSpecs
+    {
+        private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustHaveValidValidatorsAnalyzer();
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_one_of_the_specified_parameter_validators_does_not_derive_from_BindingValidator()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyValidator
+{
+    public void Validate(string value) {}
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Validators = new[] {typeof(MyValidator)})]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_all_specified_parameter_validators_derive_from_BindingValidator()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+public class MyValidator : BindingValidator<string>
+{
+    public override BindingValidationError Validate(string value) => Ok();
+}
+
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Validators = new[] {typeof(MyValidator)})]
+    public string Foo { get; set; }
+    
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_parameter_does_not_have_validators()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+    
+    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
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public string Foo { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/SystemConsoleShouldBeAvoidedAnalyzerSpecs.cs

@@ -0,0 +1,127 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests
+{
+    public class SystemConsoleShouldBeAvoidedAnalyzerSpecs
+    {
+        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 = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        Console.WriteLine(""Hello world"");
+        return default;
+    }
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_a_command_accesses_a_property_on_SystemConsole()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        Console.ForegroundColor = ConsoleColor.Black;
+        return default;
+    }
+}";
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_reports_an_error_if_a_command_calls_a_method_on_a_property_of_SystemConsole()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        Console.Error.WriteLine(""Hello world"");
+        return default;
+    }
+}";
+
+            // Act & assert
+            Analyzer.Should().ProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_command_interacts_with_the_console_through_IConsole()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        console.Output.WriteLine(""Hello world"");
+        return default;
+    }
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_IConsole_is_not_available_in_the_current_method()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public void SomeOtherMethod() => Console.WriteLine(""Test"");
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+
+        [Fact]
+        public void Analyzer_does_not_report_an_error_if_a_command_does_not_access_SystemConsole()
+        {
+            // Arrange
+            // language=cs
+            const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        return default;
+    }
+}";
+
+            // Act & assert
+            Analyzer.Should().NotProduceDiagnostics(code);
+        }
+    }
+}

CliFx.Analyzers.Tests/Utils/AnalyzerAssertions.cs

@@ -0,0 +1,174 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+using System.Reflection;
+using System.Text;
+using FluentAssertions.Execution;
+using FluentAssertions.Primitives;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Text;
+
+namespace CliFx.Analyzers.Tests.Utils
+{
+    internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer, AnalyzerAssertions>
+    {
+        protected override string Identifier { get; } = "analyzer";
+
+        public AnalyzerAssertions(DiagnosticAnalyzer analyzer)
+            : base(analyzer)
+        {
+        }
+
+        private Compilation Compile(string sourceCode)
+        {
+            // Get default system namespaces
+            var defaultSystemNamespaces = new[]
+            {
+                "System",
+                "System.Collections.Generic",
+                "System.Threading.Tasks"
+            };
+
+            // Get default CliFx namespaces
+            var defaultCliFxNamespaces = typeof(ICommand)
+                .Assembly
+                .GetTypes()
+                .Where(t => t.IsPublic)
+                .Select(t => t.Namespace)
+                .Distinct()
+                .ToArray();
+
+            // 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;
+
+            // Parse the source code
+            var ast = SyntaxFactory.ParseSyntaxTree(
+                SourceText.From(sourceCodeWithUsings),
+                CSharpParseOptions.Default
+            );
+
+            // Compile the code to IL
+            var compilation = CSharpCompilation.Create(
+                "CliFxTests_DynamicAssembly_" + Guid.NewGuid(),
+                new[] {ast},
+                new[]
+                {
+                    MetadataReference.CreateFromFile(Assembly.Load("netstandard").Location),
+                    MetadataReference.CreateFromFile(Assembly.Load("System.Runtime").Location),
+                    MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
+                    MetadataReference.CreateFromFile(typeof(Console).Assembly.Location),
+                    MetadataReference.CreateFromFile(typeof(ICommand).Assembly.Location)
+                },
+                // DLL to avoid having to define the Main() method
+                new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
+            );
+
+            var compilationErrors = compilation
+                .GetDiagnostics()
+                .Where(d => d.Severity >= DiagnosticSeverity.Error)
+                .ToArray();
+
+            if (compilationErrors.Any())
+            {
+                throw new InvalidOperationException(
+                    "Failed to compile code." +
+                    Environment.NewLine +
+                    string.Join(Environment.NewLine, compilationErrors.Select(e => e.ToString()))
+                );
+            }
+
+            return compilation;
+        }
+
+        private IReadOnlyList<Diagnostic> GetProducedDiagnostics(string sourceCode)
+        {
+            var analyzers = ImmutableArray.Create(Subject);
+            var compilation = Compile(sourceCode);
+
+            return compilation
+                .WithAnalyzers(analyzers)
+                .GetAnalyzerDiagnosticsAsync(analyzers, default)
+                .GetAwaiter()
+                .GetResult();
+        }
+
+        public void ProduceDiagnostics(string sourceCode)
+        {
+            var expectedDiagnostics = Subject.SupportedDiagnostics;
+            var producedDiagnostics = GetProducedDiagnostics(sourceCode);
+
+            var expectedDiagnosticIds = expectedDiagnostics.Select(d => d.Id).Distinct().ToArray();
+            var producedDiagnosticIds = producedDiagnostics.Select(d => d.Id).Distinct().ToArray();
+
+            var result =
+                expectedDiagnosticIds.Intersect(producedDiagnosticIds).Count() ==
+                expectedDiagnosticIds.Length;
+
+            Execute.Assertion.ForCondition(result).FailWith(() =>
+            {
+                var buffer = new StringBuilder();
+
+                buffer.AppendLine("Expected and produced diagnostics do not match.");
+                buffer.AppendLine();
+
+                buffer.AppendLine("Expected diagnostics:");
+
+                foreach (var expectedDiagnostic in expectedDiagnostics)
+                {
+                    buffer.Append("  - ");
+                    buffer.Append(expectedDiagnostic.Id);
+                    buffer.AppendLine();
+                }
+
+                buffer.AppendLine();
+
+                buffer.AppendLine("Produced diagnostics:");
+
+                foreach (var producedDiagnostic in producedDiagnostics)
+                {
+                    buffer.Append("  - ");
+                    buffer.Append(producedDiagnostic);
+                }
+
+                return new FailReason(buffer.ToString());
+            });
+        }
+
+        public void NotProduceDiagnostics(string sourceCode)
+        {
+            var producedDiagnostics = GetProducedDiagnostics(sourceCode);
+
+            var result = !producedDiagnostics.Any();
+
+            Execute.Assertion.ForCondition(result).FailWith(() =>
+            {
+                var buffer = new StringBuilder();
+
+                buffer.AppendLine("Expected no produced diagnostics.");
+                buffer.AppendLine();
+
+                buffer.AppendLine("Produced diagnostics:");
+
+                foreach (var producedDiagnostic in producedDiagnostics)
+                {
+                    buffer.Append("  - ");
+                    buffer.Append(producedDiagnostic);
+                }
+
+                return new FailReason(buffer.ToString());
+            });
+        }
+    }
+
+    internal static class AnalyzerAssertionsExtensions
+    {
+        public static AnalyzerAssertions Should(this DiagnosticAnalyzer analyzer) => new(analyzer);
+    }
+}

CliFx.Analyzers.Tests/xunit.runner.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "methodDisplayOptions": "all",
+  "methodDisplay": "method"
+}

CliFx.Analyzers/AnalyzerBase.cs

@@ -0,0 +1,40 @@
+using System.Collections.Immutable;
+using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CliFx.Analyzers
+{
+    public abstract class AnalyzerBase : DiagnosticAnalyzer
+    {
+        public DiagnosticDescriptor SupportedDiagnostic { get; }
+
+        public sealed override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; }
+
+        protected AnalyzerBase(
+            string diagnosticTitle,
+            string diagnosticMessage,
+            DiagnosticSeverity diagnosticSeverity = DiagnosticSeverity.Error)
+        {
+            SupportedDiagnostic = new DiagnosticDescriptor(
+                "CliFx_" + GetType().Name.TrimEnd("Analyzer"),
+                diagnosticTitle,
+                diagnosticMessage,
+                "CliFx",
+                diagnosticSeverity,
+                true
+            );
+
+            SupportedDiagnostics = ImmutableArray.Create(SupportedDiagnostic);
+        }
+
+        protected Diagnostic CreateDiagnostic(Location location) =>
+            Diagnostic.Create(SupportedDiagnostic, location);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.EnableConcurrentExecution();
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+        }
+    }
+}

CliFx.Analyzers/CliFx.Analyzers.csproj

@@ -1,13 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
     <Nullable>annotations</Nullable>
+    <NoWarn>$(NoWarn);RS1025;RS1026</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="3.4.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.4.0" PrivateAssets="all" />
   </ItemGroup>
 
 </Project>

CliFx.Analyzers/CommandMustBeAnnotatedAnalyzer.cs

@@ -0,0 +1,54 @@
+using System.Linq;
+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 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.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            ClassDeclarationSyntax classDeclaration,
+            ITypeSymbol type)
+        {
+            // Ignore abstract classes, because they may be used to define
+            // base implementations for commands, in which case the command
+            // attribute doesn't make sense.
+            if (type.IsAbstract)
+                return;
+
+            var implementsCommandInterface = type
+                .AllInterfaces
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+
+            var hasCommandAttribute = type
+                .GetAttributes()
+                .Select(a => a.AttributeClass)
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
+
+            // If the interface is implemented, but the attribute is missing,
+            // then it's very likely a user error.
+            if (implementsCommandInterface && !hasCommandAttribute)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(classDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandleClassDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/CommandMustImplementInterfaceAnalyzer.cs

@@ -0,0 +1,48 @@
+using System.Linq;
+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 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.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            ClassDeclarationSyntax classDeclaration,
+            ITypeSymbol type)
+        {
+            var hasCommandAttribute = type
+                .GetAttributes()
+                .Select(a => a.AttributeClass)
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
+
+            var implementsCommandInterface = type
+                .AllInterfaces
+                .Any(s => s.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.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandleClassDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/CommandSchemaAnalyzer.cs

@@ -1,297 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Collections.Immutable;
-using System.Linq;
-using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.Diagnostics;
-
-namespace CliFx.Analyzers
-{
-    [DiagnosticAnalyzer(LanguageNames.CSharp)]
-    public class CommandSchemaAnalyzer : DiagnosticAnalyzer
-    {
-        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(
-            DiagnosticDescriptors.CliFx0001,
-            DiagnosticDescriptors.CliFx0002,
-            DiagnosticDescriptors.CliFx0021,
-            DiagnosticDescriptors.CliFx0022,
-            DiagnosticDescriptors.CliFx0023,
-            DiagnosticDescriptors.CliFx0024,
-            DiagnosticDescriptors.CliFx0041,
-            DiagnosticDescriptors.CliFx0042,
-            DiagnosticDescriptors.CliFx0043,
-            DiagnosticDescriptors.CliFx0044,
-            DiagnosticDescriptors.CliFx0045
-        );
-
-        private static bool IsScalarType(ITypeSymbol typeSymbol) =>
-            KnownSymbols.IsSystemString(typeSymbol) ||
-            !typeSymbol.AllInterfaces.Select(i => i.ConstructedFrom).Any(KnownSymbols.IsSystemCollectionsGenericIEnumerable);
-
-        private static void CheckCommandParameterProperties(
-            SymbolAnalysisContext context,
-            IReadOnlyList<IPropertySymbol> properties)
-        {
-            var parameters = properties
-                .Select(p =>
-                {
-                    var attribute = p
-                        .GetAttributes()
-                        .First(a => KnownSymbols.IsCommandParameterAttribute(a.AttributeClass));
-
-                    var order = attribute
-                        .ConstructorArguments
-                        .Select(a => a.Value)
-                        .FirstOrDefault() as int?;
-
-                    var name = attribute
-                        .NamedArguments
-                        .Where(a => a.Key == "Name")
-                        .Select(a => a.Value.Value)
-                        .FirstOrDefault() as string;
-
-                    return new
-                    {
-                        Property = p,
-                        Order = order,
-                        Name = name
-                    };
-                })
-                .ToArray();
-
-            // Duplicate order
-            var duplicateOrderParameters = parameters
-                .Where(p => p.Order != null)
-                .GroupBy(p => p.Order)
-                .Where(g => g.Count() > 1)
-                .SelectMany(g => g.AsEnumerable())
-                .ToArray();
-
-            foreach (var parameter in duplicateOrderParameters)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0021, parameter.Property.Locations.First()));
-            }
-
-            // Duplicate name
-            var duplicateNameParameters = parameters
-                .Where(p => !string.IsNullOrWhiteSpace(p.Name))
-                .GroupBy(p => p.Name, StringComparer.OrdinalIgnoreCase)
-                .Where(g => g.Count() > 1)
-                .SelectMany(g => g.AsEnumerable())
-                .ToArray();
-
-            foreach (var parameter in duplicateNameParameters)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0022, parameter.Property.Locations.First()));
-            }
-
-            // Multiple non-scalar
-            var nonScalarParameters = parameters
-                .Where(p => !IsScalarType(p.Property.Type))
-                .ToArray();
-
-            if (nonScalarParameters.Length > 1)
-            {
-                foreach (var parameter in nonScalarParameters)
-                {
-                    context.ReportDiagnostic(
-                        Diagnostic.Create(DiagnosticDescriptors.CliFx0023, parameter.Property.Locations.First()));
-                }
-            }
-
-            // Non-last non-scalar
-            var nonLastNonScalarParameter = parameters
-                .OrderByDescending(a => a.Order)
-                .Skip(1)
-                .LastOrDefault(p => !IsScalarType(p.Property.Type));
-
-            if (nonLastNonScalarParameter != null)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0024, nonLastNonScalarParameter.Property.Locations.First()));
-            }
-        }
-
-        private static void CheckCommandOptionProperties(
-            SymbolAnalysisContext context,
-            IReadOnlyList<IPropertySymbol> properties)
-        {
-            var options = properties
-                .Select(p =>
-                {
-                    var attribute = p
-                        .GetAttributes()
-                        .First(a => KnownSymbols.IsCommandOptionAttribute(a.AttributeClass));
-
-                    var name = attribute
-                        .ConstructorArguments
-                        .Where(a => KnownSymbols.IsSystemString(a.Type))
-                        .Select(a => a.Value)
-                        .FirstOrDefault() as string;
-
-                    var shortName = attribute
-                        .ConstructorArguments
-                        .Where(a => KnownSymbols.IsSystemChar(a.Type))
-                        .Select(a => a.Value)
-                        .FirstOrDefault() as char?;
-
-                    var envVarName = attribute
-                        .NamedArguments
-                        .Where(a => a.Key == "EnvironmentVariableName")
-                        .Select(a => a.Value.Value)
-                        .FirstOrDefault() as string;
-
-                    return new
-                    {
-                        Property = p,
-                        Name = name,
-                        ShortName = shortName,
-                        EnvironmentVariableName = envVarName
-                    };
-                })
-                .ToArray();
-
-            // No name
-            var noNameOptions = options
-                .Where(o => string.IsNullOrWhiteSpace(o.Name) && o.ShortName == null)
-                .ToArray();
-
-            foreach (var option in noNameOptions)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0041, option.Property.Locations.First()));
-            }
-
-            // Too short name
-            var invalidNameLengthOptions = options
-                .Where(o => !string.IsNullOrWhiteSpace(o.Name) && o.Name.Length <= 1)
-                .ToArray();
-
-            foreach (var option in invalidNameLengthOptions)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0042, option.Property.Locations.First()));
-            }
-
-            // Duplicate name
-            var duplicateNameOptions = options
-                .Where(p => !string.IsNullOrWhiteSpace(p.Name))
-                .GroupBy(p => p.Name, StringComparer.OrdinalIgnoreCase)
-                .Where(g => g.Count() > 1)
-                .SelectMany(g => g.AsEnumerable())
-                .ToArray();
-
-            foreach (var option in duplicateNameOptions)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0043, option.Property.Locations.First()));
-            }
-
-            // Duplicate name
-            var duplicateShortNameOptions = options
-                .Where(p => p.ShortName != null)
-                .GroupBy(p => p.ShortName)
-                .Where(g => g.Count() > 1)
-                .SelectMany(g => g.AsEnumerable())
-                .ToArray();
-
-            foreach (var option in duplicateShortNameOptions)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0044, option.Property.Locations.First()));
-            }
-
-            // Duplicate environment variable name
-            var duplicateEnvironmentVariableNameOptions = options
-                .Where(p => !string.IsNullOrWhiteSpace(p.EnvironmentVariableName))
-                .GroupBy(p => p.EnvironmentVariableName, StringComparer.OrdinalIgnoreCase)
-                .Where(g => g.Count() > 1)
-                .SelectMany(g => g.AsEnumerable())
-                .ToArray();
-
-            foreach (var option in duplicateEnvironmentVariableNameOptions)
-            {
-                context.ReportDiagnostic(
-                    Diagnostic.Create(DiagnosticDescriptors.CliFx0045, option.Property.Locations.First()));
-            }
-        }
-
-        private static void CheckCommandType(SymbolAnalysisContext context)
-        {
-            // Named type: MyCommand
-            if (!(context.Symbol is INamedTypeSymbol namedTypeSymbol))
-                return;
-
-            // Only classes
-            if (namedTypeSymbol.TypeKind != TypeKind.Class)
-                return;
-
-            // Implements ICommand?
-            var implementsCommandInterface = namedTypeSymbol
-                .AllInterfaces
-                .Any(KnownSymbols.IsCommandInterface);
-
-            // Has CommandAttribute?
-            var hasCommandAttribute = namedTypeSymbol
-                .GetAttributes()
-                .Select(a => a.AttributeClass)
-                .Any(KnownSymbols.IsCommandAttribute);
-
-            var isValidCommandType =
-                // implements interface
-                implementsCommandInterface && (
-                    // and either abstract class or has attribute
-                    namedTypeSymbol.IsAbstract || hasCommandAttribute
-                );
-
-            if (!isValidCommandType)
-            {
-                // See if this was meant to be a command type (either interface or attribute present)
-                var isAlmostValidCommandType = implementsCommandInterface ^ hasCommandAttribute;
-
-                if (isAlmostValidCommandType && !implementsCommandInterface)
-                    context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.CliFx0001, namedTypeSymbol.Locations.First()));
-
-                if (isAlmostValidCommandType && !hasCommandAttribute)
-                    context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.CliFx0002, namedTypeSymbol.Locations.First()));
-
-                return;
-            }
-
-            var properties = namedTypeSymbol
-                .GetMembers()
-                .Where(m => m.Kind == SymbolKind.Property)
-                .OfType<IPropertySymbol>().ToArray();
-
-            // Check parameters
-            var parameterProperties = properties
-                .Where(p => p
-                    .GetAttributes()
-                    .Select(a => a.AttributeClass)
-                    .Any(KnownSymbols.IsCommandParameterAttribute))
-                .ToArray();
-
-            CheckCommandParameterProperties(context, parameterProperties);
-
-            // Check options
-            var optionsProperties = properties
-                .Where(p => p
-                    .GetAttributes()
-                    .Select(a => a.AttributeClass)
-                    .Any(KnownSymbols.IsCommandOptionAttribute))
-                .ToArray();
-
-            CheckCommandOptionProperties(context, optionsProperties);
-        }
-
-        public override void Initialize(AnalysisContext context)
-        {
-            context.EnableConcurrentExecution();
-            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
-
-            context.RegisterSymbolAction(CheckCommandType, SymbolKind.NamedType);
-        }
-    }
-}

CliFx.Analyzers/ConsoleUsageAnalyzer.cs

@@ -1,80 +0,0 @@
-using System.Collections.Immutable;
-using System.Linq;
-using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.CSharp;
-using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Diagnostics;
-
-namespace CliFx.Analyzers
-{
-    [DiagnosticAnalyzer(LanguageNames.CSharp)]
-    public class ConsoleUsageAnalyzer : DiagnosticAnalyzer
-    {
-        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(
-            DiagnosticDescriptors.CliFx0100
-        );
-
-        private static bool IsSystemConsoleInvocation(
-            SyntaxNodeAnalysisContext context,
-            InvocationExpressionSyntax invocationSyntax)
-        {
-            // Get the method member access (Console.WriteLine or Console.Error.WriteLine)
-            if (!(invocationSyntax.Expression is MemberAccessExpressionSyntax memberAccessSyntax))
-                return false;
-
-            // Get the semantic model for the invoked method
-            if (!(context.SemanticModel.GetSymbolInfo(memberAccessSyntax).Symbol is IMethodSymbol methodSymbol))
-                return false;
-
-            // Check if contained within System.Console
-            if (KnownSymbols.IsSystemConsole(methodSymbol.ContainingType))
-                return true;
-
-            // In case with Console.Error.WriteLine that wouldn't work, we need to check parent member access too
-            if (!(memberAccessSyntax.Expression is MemberAccessExpressionSyntax parentMemberAccessSyntax))
-                return false;
-
-            // Get the semantic model for the parent member
-            if (!(context.SemanticModel.GetSymbolInfo(parentMemberAccessSyntax).Symbol is IPropertySymbol propertySymbol))
-                return false;
-
-            // Check if contained within System.Console
-            if (KnownSymbols.IsSystemConsole(propertySymbol.ContainingType))
-                return true;
-
-            return false;
-        }
-
-        private static void CheckSystemConsoleUsage(SyntaxNodeAnalysisContext context)
-        {
-            if (!(context.Node is InvocationExpressionSyntax invocationSyntax))
-                return;
-
-            if (!IsSystemConsoleInvocation(context, invocationSyntax))
-                return;
-
-            // Check if IConsole is available in the scope as a viable alternative
-            var isConsoleInterfaceAvailable = invocationSyntax
-                .Ancestors()
-                .OfType<MethodDeclarationSyntax>()
-                .SelectMany(m => m.ParameterList.Parameters)
-                .Select(p => p.Type)
-                .Select(t => context.SemanticModel.GetSymbolInfo(t).Symbol)
-                .Where(s => s != null)
-                .Any(KnownSymbols.IsConsoleInterface!);
-
-            if (!isConsoleInterfaceAvailable)
-                return;
-
-            context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.CliFx0100, invocationSyntax.GetLocation()));
-        }
-
-        public override void Initialize(AnalysisContext context)
-        {
-            context.EnableConcurrentExecution();
-            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
-
-            context.RegisterSyntaxNodeAction(CheckSystemConsoleUsage, SyntaxKind.InvocationExpression);
-        }
-    }
-}

CliFx.Analyzers/DiagnosticDescriptors.cs

@@ -1,79 +0,0 @@
-using Microsoft.CodeAnalysis;
-
-namespace CliFx.Analyzers
-{
-    public static class DiagnosticDescriptors
-    {
-        public static readonly DiagnosticDescriptor CliFx0001 =
-            new DiagnosticDescriptor(nameof(CliFx0001),
-                "Type must implement the 'CliFx.ICommand' interface in order to be a valid command",
-                "Type must implement the 'CliFx.ICommand' interface in order to be a valid command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0002 =
-            new DiagnosticDescriptor(nameof(CliFx0002),
-                "Type must be annotated with the 'CliFx.Attributes.CommandAttribute' in order to be a valid command",
-                "Type must be annotated with the 'CliFx.Attributes.CommandAttribute' in order to be a valid command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0021 =
-            new DiagnosticDescriptor(nameof(CliFx0021),
-                "Parameter order must be unique within its command",
-                "Parameter order must be unique within its command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0022 =
-            new DiagnosticDescriptor(nameof(CliFx0022),
-                "Parameter order must have unique name within its command",
-                "Parameter order must have unique name within its command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0023 =
-            new DiagnosticDescriptor(nameof(CliFx0023),
-                "Only one non-scalar parameter per command is allowed",
-                "Only one non-scalar parameter per command is allowed",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0024 =
-            new DiagnosticDescriptor(nameof(CliFx0024),
-                "Non-scalar parameter must be last in order",
-                "Non-scalar parameter must be last in order",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0041 =
-            new DiagnosticDescriptor(nameof(CliFx0041),
-                "Option must have a name or short name specified",
-                "Option must have a name or short name specified",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0042 =
-            new DiagnosticDescriptor(nameof(CliFx0042),
-                "Option name must be at least 2 characters long",
-                "Option name must be at least 2 characters long",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0043 =
-            new DiagnosticDescriptor(nameof(CliFx0043),
-                "Option name must be unique within its command",
-                "Option name must be unique within its command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0044 =
-            new DiagnosticDescriptor(nameof(CliFx0044),
-                "Option short name must be unique within its command",
-                "Option short name must be unique within its command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0045 =
-            new DiagnosticDescriptor(nameof(CliFx0045),
-                "Option environment variable name must be unique within its command",
-                "Option environment variable name must be unique within its command",
-                "Usage", DiagnosticSeverity.Error, true);
-
-        public static readonly DiagnosticDescriptor CliFx0100 =
-            new DiagnosticDescriptor(nameof(CliFx0100),
-                "Use the provided IConsole abstraction instead of System.Console to ensure that the command can be tested in isolation",
-                "Use the provided IConsole abstraction instead of System.Console to ensure that the command can be tested in isolation",
-                "Usage", DiagnosticSeverity.Warning, true);
-    }
-}

CliFx.Analyzers/Internal/RoslynExtensions.cs

@@ -1,11 +0,0 @@
-using System;
-using Microsoft.CodeAnalysis;
-
-namespace CliFx.Analyzers.Internal
-{
-    internal static class RoslynExtensions
-    {
-        public static bool DisplayNameMatches(this ISymbol symbol, string name) =>
-            string.Equals(symbol.ToDisplayString(), name, StringComparison.Ordinal);
-    }
-}

CliFx.Analyzers/KnownSymbols.cs

@@ -1,37 +0,0 @@
-using CliFx.Analyzers.Internal;
-using Microsoft.CodeAnalysis;
-
-namespace CliFx.Analyzers
-{
-    public static class KnownSymbols
-    {
-        public static bool IsSystemString(ISymbol symbol) =>
-            symbol.DisplayNameMatches("string") ||
-            symbol.DisplayNameMatches("System.String");
-
-        public static bool IsSystemChar(ISymbol symbol) =>
-            symbol.DisplayNameMatches("char") ||
-            symbol.DisplayNameMatches("System.Char");
-
-        public static bool IsSystemCollectionsGenericIEnumerable(ISymbol symbol) =>
-            symbol.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>");
-
-        public static bool IsSystemConsole(ISymbol symbol) =>
-            symbol.DisplayNameMatches("System.Console");
-
-        public static bool IsConsoleInterface(ISymbol symbol) =>
-            symbol.DisplayNameMatches("CliFx.IConsole");
-
-        public static bool IsCommandInterface(ISymbol symbol) =>
-            symbol.DisplayNameMatches("CliFx.ICommand");
-
-        public static bool IsCommandAttribute(ISymbol symbol) =>
-            symbol.DisplayNameMatches("CliFx.Attributes.CommandAttribute");
-
-        public static bool IsCommandParameterAttribute(ISymbol symbol) =>
-            symbol.DisplayNameMatches("CliFx.Attributes.CommandParameterAttribute");
-
-        public static bool IsCommandOptionAttribute(ISymbol symbol) =>
-            symbol.DisplayNameMatches("CliFx.Attributes.CommandOptionAttribute");
-    }
-}

CliFx.Analyzers/ObjectModel/CommandOptionSymbol.cs

@@ -0,0 +1,83 @@
+using System.Collections.Generic;
+using Microsoft.CodeAnalysis;
+using System.Linq;
+using CliFx.Analyzers.Utils.Extensions;
+
+namespace CliFx.Analyzers.ObjectModel
+{
+    internal partial class CommandOptionSymbol
+    {
+        public string? Name { get; }
+
+        public char? ShortName { get; }
+
+        public ITypeSymbol? ConverterType { get; }
+
+        public IReadOnlyList<ITypeSymbol> ValidatorTypes { get; }
+
+        public CommandOptionSymbol(
+            string? name,
+            char? shortName,
+            ITypeSymbol? converterType,
+            IReadOnlyList<ITypeSymbol> validatorTypes)
+        {
+            Name = name;
+            ShortName = shortName;
+            ConverterType = converterType;
+            ValidatorTypes = validatorTypes;
+        }
+    }
+
+    internal partial class CommandOptionSymbol
+    {
+        private static AttributeData? TryGetOptionAttribute(IPropertySymbol property) =>
+            property
+                .GetAttributes()
+                .FirstOrDefault(a => a.AttributeClass.DisplayNameMatches(SymbolNames.CliFxCommandOptionAttribute));
+
+        private static CommandOptionSymbol FromAttribute(AttributeData attribute)
+        {
+            var name = attribute
+                .ConstructorArguments
+                .Where(a => a.Type.DisplayNameMatches("string") || a.Type.DisplayNameMatches("System.String"))
+                .Select(a => a.Value)
+                .FirstOrDefault() as string;
+
+            var shortName = attribute
+                .ConstructorArguments
+                .Where(a => a.Type.DisplayNameMatches("char") || a.Type.DisplayNameMatches("System.Char"))
+                .Select(a => a.Value)
+                .FirstOrDefault() as char?;
+
+            var converter = attribute
+                .NamedArguments
+                .Where(a => a.Key == "Converter")
+                .Select(a => a.Value.Value)
+                .Cast<ITypeSymbol?>()
+                .FirstOrDefault();
+
+            var validators = attribute
+                .NamedArguments
+                .Where(a => a.Key == "Validators")
+                .SelectMany(a => a.Value.Values)
+                .Select(c => c.Value)
+                .Cast<ITypeSymbol>()
+                .ToArray();
+
+            return new CommandOptionSymbol(name, shortName, converter, validators);
+        }
+
+        public static CommandOptionSymbol? TryResolve(IPropertySymbol property)
+        {
+            var attribute = TryGetOptionAttribute(property);
+
+            if (attribute is null)
+                return null;
+
+            return FromAttribute(attribute);
+        }
+
+        public static bool IsOptionProperty(IPropertySymbol property) =>
+            TryGetOptionAttribute(property) is not null;
+    }
+}

CliFx.Analyzers/ObjectModel/CommandParameterSymbol.cs

@@ -0,0 +1,82 @@
+using System.Collections.Generic;
+using System.Linq;
+using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.Analyzers.ObjectModel
+{
+    internal partial class CommandParameterSymbol
+    {
+        public int Order { get; }
+
+        public string? Name { get; }
+
+        public ITypeSymbol? ConverterType { get; }
+
+        public IReadOnlyList<ITypeSymbol> ValidatorTypes { get; }
+
+        public CommandParameterSymbol(
+            int order,
+            string? name,
+            ITypeSymbol? converterType,
+            IReadOnlyList<ITypeSymbol> validatorTypes)
+        {
+            Order = order;
+            Name = name;
+            ConverterType = converterType;
+            ValidatorTypes = validatorTypes;
+        }
+    }
+
+    internal partial class CommandParameterSymbol
+    {
+        private static AttributeData? TryGetParameterAttribute(IPropertySymbol property) =>
+            property
+                .GetAttributes()
+                .FirstOrDefault(a => a.AttributeClass.DisplayNameMatches(SymbolNames.CliFxCommandParameterAttribute));
+
+        private static CommandParameterSymbol FromAttribute(AttributeData attribute)
+        {
+            var order = (int) attribute
+                .ConstructorArguments
+                .Select(a => a.Value)
+                .First()!;
+
+            var name = attribute
+                .NamedArguments
+                .Where(a => a.Key == "Name")
+                .Select(a => a.Value.Value)
+                .FirstOrDefault() as string;
+
+            var converter = attribute
+                .NamedArguments
+                .Where(a => a.Key == "Converter")
+                .Select(a => a.Value.Value)
+                .Cast<ITypeSymbol?>()
+                .FirstOrDefault();
+
+            var validators = attribute
+                .NamedArguments
+                .Where(a => a.Key == "Validators")
+                .SelectMany(a => a.Value.Values)
+                .Select(c => c.Value)
+                .Cast<ITypeSymbol>()
+                .ToArray();
+
+            return new CommandParameterSymbol(order, name, converter, validators);
+        }
+
+        public static CommandParameterSymbol? TryResolve(IPropertySymbol property)
+        {
+            var attribute = TryGetParameterAttribute(property);
+
+            if (attribute is null)
+                return null;
+
+            return FromAttribute(attribute);
+        }
+
+        public static bool IsParameterProperty(IPropertySymbol property) =>
+            TryGetParameterAttribute(property) is not null;
+    }
+}

CliFx.Analyzers/ObjectModel/SymbolNames.cs

@@ -0,0 +1,15 @@
+namespace CliFx.Analyzers.ObjectModel
+{
+    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 CliFxCommandOptionAttribute = "CliFx.Attributes.CommandOptionAttribute";
+        public const string CliFxConsoleInterface = "CliFx.Infrastructure.IConsole";
+        public const string CliFxBindingConverterInterface = "CliFx.Extensibility.IBindingConverter";
+        public const string CliFxBindingConverterClass = "CliFx.Extensibility.BindingConverter<T>";
+        public const string CliFxBindingValidatorInterface = "CliFx.Extensibility.IBindingValidator";
+        public const string CliFxBindingValidatorClass = "CliFx.Extensibility.BindingValidator<T>";
+    }
+}

CliFx.Analyzers/OptionMustBeInsideCommandAnalyzer.cs

@@ -0,0 +1,51 @@
+using System.Linq;
+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 OptionMustBeInsideCommandAnalyzer : AnalyzerBase
+    {
+        public OptionMustBeInsideCommandAnalyzer()
+            : base(
+                "Options must be defined inside commands",
+                $"This option must be defined inside a class that implements `{SymbolNames.CliFxCommandInterface}`.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            if (property.ContainingType.IsAbstract)
+                return;
+
+            if (!CommandOptionSymbol.IsOptionProperty(property))
+                return;
+
+            var isInsideCommand = property
+                .ContainingType
+                .AllInterfaces
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+
+            if (!isInsideCommand)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveNameOrShortNameAnalyzer.cs

@@ -0,0 +1,40 @@
+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 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.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            if (string.IsNullOrWhiteSpace(option.Name) && option.ShortName is null)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveUniqueNameAnalyzer.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Linq;
+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 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).")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            if (string.IsNullOrWhiteSpace(option.Name))
+                return;
+
+            var otherProperties = property
+                .ContainingType
+                .GetMembers()
+                .OfType<IPropertySymbol>()
+                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+                .ToArray();
+
+            foreach (var otherProperty in otherProperties)
+            {
+                var otherOption = CommandOptionSymbol.TryResolve(otherProperty);
+                if (otherOption is null)
+                    continue;
+
+                if (string.IsNullOrWhiteSpace(otherOption.Name))
+                    continue;
+
+                if (string.Equals(option.Name, otherOption.Name, StringComparison.OrdinalIgnoreCase))
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveUniqueShortNameAnalyzer.cs

@@ -0,0 +1,64 @@
+using System.Linq;
+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 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).")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            if (option.ShortName is null)
+                return;
+
+            var otherProperties = property
+                .ContainingType
+                .GetMembers()
+                .OfType<IPropertySymbol>()
+                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+                .ToArray();
+
+            foreach (var otherProperty in otherProperties)
+            {
+                var otherOption = CommandOptionSymbol.TryResolve(otherProperty);
+                if (otherOption is null)
+                    continue;
+
+                if (otherOption.ShortName is null)
+                    continue;
+
+                if (option.ShortName == otherOption.ShortName)
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveValidConverterAnalyzer.cs

@@ -0,0 +1,50 @@
+using System.Linq;
+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 OptionMustHaveValidConverterAnalyzer : AnalyzerBase
+    {
+        public OptionMustHaveValidConverterAnalyzer()
+            : base(
+                $"Option converters must derive from `{SymbolNames.CliFxBindingConverterClass}`",
+                $"Converter specified for this option must derive from `{SymbolNames.CliFxBindingConverterClass}`.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            if (option.ConverterType is null)
+                return;
+
+            // We check against an internal interface because checking against a generic class is a pain
+            var converterImplementsInterface = option
+                .ConverterType
+                .AllInterfaces
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingConverterInterface));
+
+            if (!converterImplementsInterface)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveValidNameAnalyzer.cs

@@ -0,0 +1,43 @@
+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 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.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            if (string.IsNullOrWhiteSpace(option.Name))
+                return;
+
+            if (option.Name.Length < 2 || !char.IsLetter(option.Name[0]))
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveValidShortNameAnalyzer.cs

@@ -0,0 +1,43 @@
+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 OptionMustHaveValidShortNameAnalyzer : AnalyzerBase
+    {
+        public OptionMustHaveValidShortNameAnalyzer()
+            : base(
+                "Option short names must be letter characters",
+                "This option's short name must be a single letter character.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            if (option.ShortName is null)
+                return;
+
+            if (!char.IsLetter(option.ShortName.Value))
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/OptionMustHaveValidValidatorsAnalyzer.cs

@@ -0,0 +1,52 @@
+using System.Linq;
+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 OptionMustHaveValidValidatorsAnalyzer : AnalyzerBase
+    {
+        public OptionMustHaveValidValidatorsAnalyzer()
+            : base(
+                $"Option validators must derive from `{SymbolNames.CliFxBindingValidatorClass}`",
+                $"All validators specified for this option must derive from `{SymbolNames.CliFxBindingValidatorClass}`.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var option = CommandOptionSymbol.TryResolve(property);
+            if (option is null)
+                return;
+
+            foreach (var validatorType in option.ValidatorTypes)
+            {
+                // We check against an internal interface because checking against a generic class is a pain
+                var validatorImplementsInterface = validatorType
+                    .AllInterfaces
+                    .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingValidatorInterface));
+
+                if (!validatorImplementsInterface)
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+
+                    // No need to report multiple identical diagnostics on the same node
+                    break;
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustBeInsideCommandAnalyzer.cs

@@ -0,0 +1,51 @@
+using System.Linq;
+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 ParameterMustBeInsideCommandAnalyzer : AnalyzerBase
+    {
+        public ParameterMustBeInsideCommandAnalyzer()
+            : base(
+                "Parameters must be defined inside commands",
+                $"This parameter must be defined inside a class that implements `{SymbolNames.CliFxCommandInterface}`.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            if (property.ContainingType.IsAbstract)
+                return;
+
+            if (!CommandParameterSymbol.IsParameterProperty(property))
+                return;
+
+            var isInsideCommand = property
+                .ContainingType
+                .AllInterfaces
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+
+            if (!isInsideCommand)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustBeLastIfNonScalarAnalyzer.cs

@@ -0,0 +1,68 @@
+using System.Linq;
+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 ParameterMustBeLastIfNonScalarAnalyzer : AnalyzerBase
+    {
+        public ParameterMustBeLastIfNonScalarAnalyzer()
+            : base(
+                "Parameters of non-scalar types must be last in order",
+                "This parameter has a non-scalar type so it must be last in order (its order must be highest within the command).")
+        {
+        }
+
+        private static bool IsScalar(ITypeSymbol type) =>
+            type.DisplayNameMatches("string") ||
+            type.DisplayNameMatches("System.String") ||
+            !type.AllInterfaces
+                .Select(i => i.ConstructedFrom)
+                .Any(s => s.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            if (IsScalar(property.Type))
+                return;
+
+            var parameter = CommandParameterSymbol.TryResolve(property);
+            if (parameter is null)
+                return;
+
+            var otherProperties = property
+                .ContainingType
+                .GetMembers()
+                .OfType<IPropertySymbol>()
+                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+                .ToArray();
+
+            foreach (var otherProperty in otherProperties)
+            {
+                var otherParameter = CommandParameterSymbol.TryResolve(otherProperty);
+                if (otherParameter is null)
+                    continue;
+
+                if (otherParameter.Order > parameter.Order)
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustBeSingleIfNonScalarAnalyzer.cs

@@ -0,0 +1,66 @@
+using System.Linq;
+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 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.")
+        {
+        }
+
+        private static bool IsScalar(ITypeSymbol type) =>
+            type.DisplayNameMatches("string") ||
+            type.DisplayNameMatches("System.String") ||
+            !type.AllInterfaces
+                .Select(i => i.ConstructedFrom)
+                .Any(s => s.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            if (!CommandParameterSymbol.IsParameterProperty(property))
+                return;
+
+            if (IsScalar(property.Type))
+                return;
+
+            var otherProperties = property
+                .ContainingType
+                .GetMembers()
+                .OfType<IPropertySymbol>()
+                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+                .ToArray();
+
+            foreach (var otherProperty in otherProperties)
+            {
+                if (!CommandParameterSymbol.IsParameterProperty(otherProperty))
+                    continue;
+
+                if (!IsScalar(otherProperty.Type))
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustHaveUniqueNameAnalyzer.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Linq;
+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 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).")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            var parameter = CommandParameterSymbol.TryResolve(property);
+            if (parameter is null)
+                return;
+
+            if (string.IsNullOrWhiteSpace(parameter.Name))
+                return;
+
+            var otherProperties = property
+                .ContainingType
+                .GetMembers()
+                .OfType<IPropertySymbol>()
+                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+                .ToArray();
+
+            foreach (var otherProperty in otherProperties)
+            {
+                var otherParameter = CommandParameterSymbol.TryResolve(otherProperty);
+                if (otherParameter is null)
+                    continue;
+
+                if (string.IsNullOrWhiteSpace(otherParameter.Name))
+                    continue;
+
+                if (string.Equals(parameter.Name, otherParameter.Name, StringComparison.OrdinalIgnoreCase))
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustHaveUniqueOrderAnalyzer.cs

@@ -0,0 +1,58 @@
+using System.Linq;
+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 ParameterMustHaveUniqueOrderAnalyzer : AnalyzerBase
+    {
+        public ParameterMustHaveUniqueOrderAnalyzer()
+            : base(
+                "Parameters must have unique order",
+                "This parameter's order must be unique within the command.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            if (property.ContainingType is null)
+                return;
+
+            var parameter = CommandParameterSymbol.TryResolve(property);
+            if (parameter is null)
+                return;
+
+            var otherProperties = property
+                .ContainingType
+                .GetMembers()
+                .OfType<IPropertySymbol>()
+                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
+                .ToArray();
+
+            foreach (var otherProperty in otherProperties)
+            {
+                var otherParameter = CommandParameterSymbol.TryResolve(otherProperty);
+                if (otherParameter is null)
+                    continue;
+
+                if (parameter.Order == otherParameter.Order)
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustHaveValidConverterAnalyzer.cs

@@ -0,0 +1,50 @@
+using System.Linq;
+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 ParameterMustHaveValidConverterAnalyzer : AnalyzerBase
+    {
+        public ParameterMustHaveValidConverterAnalyzer()
+            : base(
+                $"Parameter converters must derive from `{SymbolNames.CliFxBindingConverterClass}`",
+                $"Converter specified for this parameter must derive from `{SymbolNames.CliFxBindingConverterClass}`.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var parameter = CommandParameterSymbol.TryResolve(property);
+            if (parameter is null)
+                return;
+
+            if (parameter.ConverterType is null)
+                return;
+
+            // We check against an internal interface because checking against a generic class is a pain
+            var converterImplementsInterface = parameter
+                .ConverterType
+                .AllInterfaces
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingConverterInterface));
+
+            if (!converterImplementsInterface)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/ParameterMustHaveValidValidatorsAnalyzer.cs

@@ -0,0 +1,52 @@
+using System.Linq;
+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 ParameterMustHaveValidValidatorsAnalyzer : AnalyzerBase
+    {
+        public ParameterMustHaveValidValidatorsAnalyzer()
+            : base(
+                $"Parameter validators must derive from `{SymbolNames.CliFxBindingValidatorClass}`",
+                $"All validators specified for this parameter must derive from `{SymbolNames.CliFxBindingValidatorClass}`.")
+        {
+        }
+
+        private void Analyze(
+            SyntaxNodeAnalysisContext context,
+            PropertyDeclarationSyntax propertyDeclaration,
+            IPropertySymbol property)
+        {
+            var parameter = CommandParameterSymbol.TryResolve(property);
+            if (parameter is null)
+                return;
+
+            foreach (var validatorType in parameter.ValidatorTypes)
+            {
+                // We check against an internal interface because checking against a generic class is a pain
+                var validatorImplementsInterface = validatorType
+                    .AllInterfaces
+                    .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingValidatorInterface));
+
+                if (!validatorImplementsInterface)
+                {
+                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+
+                    // No need to report multiple identical diagnostics on the same node
+                    break;
+                }
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.HandlePropertyDeclaration(Analyze);
+        }
+    }
+}

CliFx.Analyzers/SystemConsoleShouldBeAvoidedAnalyzer.cs

@@ -0,0 +1,78 @@
+using System.Linq;
+using CliFx.Analyzers.ObjectModel;
+using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CliFx.Analyzers
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class SystemConsoleShouldBeAvoidedAnalyzer : AnalyzerBase
+    {
+        public SystemConsoleShouldBeAvoidedAnalyzer()
+            : 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)
+        {
+        }
+
+        private MemberAccessExpressionSyntax? TryGetSystemConsoleMemberAccess(
+            SyntaxNodeAnalysisContext context,
+            SyntaxNode node)
+        {
+            var currentNode = node;
+
+            while (currentNode is MemberAccessExpressionSyntax memberAccess)
+            {
+                var member = context.SemanticModel.GetSymbolInfo(memberAccess).Symbol;
+
+                if (member?.ContainingType?.DisplayNameMatches("System.Console") == true)
+                {
+                    return memberAccess;
+                }
+
+                // Get inner expression, which may be another member access expression.
+                // Example: System.Console.Error
+                //          ~~~~~~~~~~~~~~          <- inner member access expression
+                //          --------------------    <- outer member access expression
+                currentNode = memberAccess.Expression;
+            }
+
+            return null;
+        }
+
+        private void Analyze(SyntaxNodeAnalysisContext context)
+        {
+            // Try to get a member access on System.Console in the current expression,
+            // or in any of its inner expressions.
+            var systemConsoleMemberAccess = TryGetSystemConsoleMemberAccess(context, context.Node);
+            if (systemConsoleMemberAccess is null)
+                return;
+
+            // Check if IConsole is available in scope as an alternative to System.Console
+            var isConsoleInterfaceAvailable = context
+                .Node
+                .Ancestors()
+                .OfType<MethodDeclarationSyntax>()
+                .SelectMany(m => m.ParameterList.Parameters)
+                .Select(p => p.Type)
+                .Select(t => context.SemanticModel.GetSymbolInfo(t).Symbol)
+                .Where(s => s is not null)
+                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxConsoleInterface));
+
+            if (isConsoleInterfaceAvailable)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(systemConsoleMemberAccess.GetLocation()));
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            base.Initialize(context);
+            context.RegisterSyntaxNodeAction(Analyze, SyntaxKind.SimpleMemberAccessExpression);
+        }
+    }
+}

CliFx.Analyzers/Utils/Extensions/RoslynExtensions.cs

@@ -0,0 +1,53 @@
+using System;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CliFx.Analyzers.Utils.Extensions
+{
+    internal static class RoslynExtensions
+    {
+        public static bool DisplayNameMatches(this ISymbol symbol, string name) =>
+            string.Equals(
+                // Fully qualified name, without `global::`
+                symbol.ToDisplayString(SymbolDisplayFormat.CSharpErrorMessageFormat),
+                name,
+                StringComparison.Ordinal
+            );
+
+        public static void HandleClassDeclaration(
+            this AnalysisContext analysisContext,
+            Action<SyntaxNodeAnalysisContext, ClassDeclarationSyntax, ITypeSymbol> analyze)
+        {
+            analysisContext.RegisterSyntaxNodeAction(ctx =>
+            {
+                if (ctx.Node is not ClassDeclarationSyntax classDeclaration)
+                    return;
+
+                var type = ctx.SemanticModel.GetDeclaredSymbol(classDeclaration);
+                if (type is null)
+                    return;
+
+                analyze(ctx, classDeclaration, type);
+            }, SyntaxKind.ClassDeclaration);
+        }
+
+        public static void HandlePropertyDeclaration(
+            this AnalysisContext analysisContext,
+            Action<SyntaxNodeAnalysisContext, PropertyDeclarationSyntax, IPropertySymbol> analyze)
+        {
+            analysisContext.RegisterSyntaxNodeAction(ctx =>
+            {
+                if (ctx.Node is not PropertyDeclarationSyntax propertyDeclaration)
+                    return;
+
+                var property = ctx.SemanticModel.GetDeclaredSymbol(propertyDeclaration);
+                if (property is null)
+                    return;
+
+                analyze(ctx, propertyDeclaration, property);
+            }, SyntaxKind.PropertyDeclaration);
+        }
+    }
+}

CliFx.Analyzers/Utils/Extensions/StringExtensions.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace CliFx.Analyzers.Utils.Extensions
+{
+    internal static class StringExtensions
+    {
+        public static string TrimEnd(
+            this string str,
+            string sub,
+            StringComparison comparison = StringComparison.Ordinal)
+        {
+            while (str.EndsWith(sub, comparison))
+                str = str.Substring(0, str.Length - sub.Length);
+
+            return str;
+        }
+    }
+}

CliFx.Benchmarks/Benchmarks.CliFx.cs

@@ -0,0 +1,33 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Benchmarks
+{
+    public partial class Benchmarks
+    {
+        [Command]
+        public class CliFxCommand : ICommand
+        {
+            [CommandOption("str", 's')]
+            public string? StrOption { get; set; }
+
+            [CommandOption("int", 'i')]
+            public int IntOption { get; set; }
+
+            [CommandOption("bool", 'b')]
+            public bool BoolOption { get; set; }
+
+            public ValueTask ExecuteAsync(IConsole console) => default;
+        }
+
+        [Benchmark(Description = "CliFx", Baseline = true)]
+        public async ValueTask<int> ExecuteWithCliFx() =>
+            await new CliApplicationBuilder()
+                .AddCommand<CliFxCommand>()
+                .Build()
+                .RunAsync(Arguments, new Dictionary<string, string>());
+    }
+}

CliFx.Benchmarks/Benchmarks.Clipr.cs

@@ -0,0 +1,27 @@
+using BenchmarkDotNet.Attributes;
+using clipr;
+
+namespace CliFx.Benchmarks
+{
+    public partial class Benchmarks
+    {
+        public class CliprCommand
+        {
+            [NamedArgument('s', "str")]
+            public string? StrOption { get; set; }
+
+            [NamedArgument('i', "int")]
+            public int IntOption { get; set; }
+
+            [NamedArgument('b', "bool", Constraint = NumArgsConstraint.Optional, Const = true)]
+            public bool BoolOption { get; set; }
+
+            public void Execute()
+            {
+            }
+        }
+
+        [Benchmark(Description = "Clipr")]
+        public void ExecuteWithClipr() => CliParser.Parse<CliprCommand>(Arguments).Execute();
+    }
+}

CliFx.Benchmarks/Benchmarks.Cocona.cs

@@ -0,0 +1,24 @@
+using BenchmarkDotNet.Attributes;
+using Cocona;
+
+namespace CliFx.Benchmarks
+{
+    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)
+            {
+            }
+        }
+
+        [Benchmark(Description = "Cocona")]
+        public void ExecuteWithCocona() => CoconaApp.Run<CoconaCommand>(Arguments);
+    }
+}

CliFx.Benchmarks/Benchmarks.CommandLineParser.cs

@@ -0,0 +1,30 @@
+using BenchmarkDotNet.Attributes;
+using CommandLine;
+
+namespace CliFx.Benchmarks
+{
+    public partial class Benchmarks
+    {
+        public class CommandLineParserCommand
+        {
+            [Option('s', "str")]
+            public string? StrOption { get; set; }
+
+            [Option('i', "int")]
+            public int IntOption { get; set; }
+
+            [Option('b', "bool")]
+            public bool BoolOption { get; set; }
+
+            public void Execute()
+            {
+            }
+        }
+
+        [Benchmark(Description = "CommandLineParser")]
+        public void ExecuteWithCommandLineParser() =>
+            new Parser()
+                .ParseArguments(Arguments, typeof(CommandLineParserCommand))
+                .WithParsed<CommandLineParserCommand>(c => c.Execute());
+    }
+}

CliFx.Benchmarks/Benchmarks.McMaster.cs

@@ -0,0 +1,25 @@
+using BenchmarkDotNet.Attributes;
+using McMaster.Extensions.CommandLineUtils;
+
+namespace CliFx.Benchmarks
+{
+    public partial class Benchmarks
+    {
+        public class McMasterCommand
+        {
+            [Option("--str|-s")]
+            public string? StrOption { get; set; }
+
+            [Option("--int|-i")]
+            public int IntOption { get; set; }
+
+            [Option("--bool|-b")]
+            public bool BoolOption { get; set; }
+
+            public int OnExecute() => 0;
+        }
+
+        [Benchmark(Description = "McMaster.Extensions.CommandLineUtils")]
+        public int ExecuteWithMcMaster() => CommandLineApplication.Execute<McMasterCommand>(Arguments);
+    }
+}

CliFx.Benchmarks/Benchmarks.PowerArgs.cs

@@ -0,0 +1,27 @@
+using BenchmarkDotNet.Attributes;
+using PowerArgs;
+
+namespace CliFx.Benchmarks
+{
+    public partial class Benchmarks
+    {
+        public class PowerArgsCommand
+        {
+            [ArgShortcut("--str"), ArgShortcut("-s")]
+            public string? StrOption { get; set; }
+
+            [ArgShortcut("--int"), ArgShortcut("-i")]
+            public int IntOption { get; set; }
+
+            [ArgShortcut("--bool"), ArgShortcut("-b")]
+            public bool BoolOption { get; set; }
+
+            public void Main()
+            {
+            }
+        }
+
+        [Benchmark(Description = "PowerArgs")]
+        public void ExecuteWithPowerArgs() => Args.InvokeMain<PowerArgsCommand>(Arguments);
+    }
+}

CliFx.Benchmarks/Benchmarks.SystemCommandLine.cs

@@ -0,0 +1,44 @@
+using System.CommandLine;
+using System.CommandLine.Invocation;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+
+namespace CliFx.Benchmarks
+{
+    public partial class Benchmarks
+    {
+        public class SystemCommandLineCommand
+        {
+            public static int ExecuteHandler(string s, int i, bool b) => 0;
+
+            public Task<int> ExecuteAsync(string[] args)
+            {
+                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>()
+                    }
+                };
+
+                command.Handler = CommandHandler.Create(
+                    typeof(SystemCommandLineCommand).GetMethod(nameof(ExecuteHandler))!
+                );
+
+                return command.InvokeAsync(args);
+            }
+        }
+
+        [Benchmark(Description = "System.CommandLine")]
+        public async Task<int> ExecuteWithSystemCommandLine() =>
+            await new SystemCommandLineCommand().ExecuteAsync(Arguments);
+    }
+}

CliFx.Benchmarks/Benchmarks.cs

@@ -1,52 +1,20 @@
-using System.Collections.Generic;
+using BenchmarkDotNet.Attributes;
-using System.Threading.Tasks;
-using BenchmarkDotNet.Attributes;
 using BenchmarkDotNet.Configs;
 using BenchmarkDotNet.Order;
 using BenchmarkDotNet.Running;
-using CliFx.Benchmarks.Commands;
-using CommandLine;
 
 namespace CliFx.Benchmarks
 {
-    [SimpleJob]
     [RankColumn]
     [Orderer(SummaryOrderPolicy.FastestToSlowest)]
-    public class Benchmarks
+    public partial class Benchmarks
     {
         private static readonly string[] Arguments = {"--str", "hello world", "-i", "13", "-b"};
 
-        [Benchmark(Description = "CliFx", Baseline = true)]
+        public static void Main() => BenchmarkRunner.Run<Benchmarks>(
-        public async ValueTask<int> ExecuteWithCliFx() =>
+            DefaultConfig
-            await new CliApplicationBuilder().AddCommand(typeof(CliFxCommand)).Build().RunAsync(Arguments, new Dictionary<string, string>());
+                .Instance
-
+                .With(ConfigOptions.DisableOptimizationsValidator)
-        [Benchmark(Description = "System.CommandLine")]
+        );
-        public async Task<int> ExecuteWithSystemCommandLine() =>
-            await new SystemCommandLineCommand().ExecuteAsync(Arguments);
-
-        [Benchmark(Description = "McMaster.Extensions.CommandLineUtils")]
-        public int ExecuteWithMcMaster() =>
-            McMaster.Extensions.CommandLineUtils.CommandLineApplication.Execute<McMasterCommand>(Arguments);
-
-        [Benchmark(Description = "CommandLineParser")]
-        public void ExecuteWithCommandLineParser() =>
-            new Parser()
-                .ParseArguments(Arguments, typeof(CommandLineParserCommand))
-                .WithParsed<CommandLineParserCommand>(c => c.Execute());
-
-        [Benchmark(Description = "PowerArgs")]
-        public void ExecuteWithPowerArgs() =>
-            PowerArgs.Args.InvokeMain<PowerArgsCommand>(Arguments);
-
-        [Benchmark(Description = "Clipr")]
-        public void ExecuteWithClipr() =>
-            clipr.CliParser.Parse<CliprCommand>(Arguments).Execute();
-
-        [Benchmark(Description = "Cocona")]
-        public void ExecuteWithCocona() =>
-            Cocona.CoconaApp.Run<CoconaCommand>(Arguments);
-
-        public static void Main() =>
-            BenchmarkRunner.Run<Benchmarks>(DefaultConfig.Instance.With(ConfigOptions.DisableOptimizationsValidator));
     }
 }

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -1,19 +1,18 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.12.0" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.12.1" />
     <PackageReference Include="clipr" Version="1.6.1" />
-    <PackageReference Include="Cocona" Version="1.3.0" />
+    <PackageReference Include="Cocona" Version="1.5.0" />
-    <PackageReference Include="CommandLineParser" Version="2.7.82" />
+    <PackageReference Include="CommandLineParser" Version="2.8.0" />
-    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="2.6.0" />
+    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="3.1.0" />
     <PackageReference Include="PowerArgs" Version="3.6.0" />
-    <PackageReference Include="System.CommandLine.Experimental" Version="0.3.0-alpha.19317.1" />
+    <PackageReference Include="System.CommandLine" Version="2.0.0-beta1.20574.7" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Benchmarks/Commands/CliFxCommand.cs

@@ -1,20 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-
-namespace CliFx.Benchmarks.Commands
-{
-    [Command]
-    public class CliFxCommand : ICommand
-    {
-        [CommandOption("str", 's')]
-        public string? StrOption { get; set; }
-
-        [CommandOption("int", 'i')]
-        public int IntOption { get; set; }
-
-        [CommandOption("bool", 'b')]
-        public bool BoolOption { get; set; }
-
-        public ValueTask ExecuteAsync(IConsole console) => default;
-    }
-}

CliFx.Benchmarks/Commands/CliprCommand.cs

@@ -1,20 +0,0 @@
-using clipr;
-
-namespace CliFx.Benchmarks.Commands
-{
-    public class CliprCommand
-    {
-        [NamedArgument('s', "str")]
-        public string? StrOption { get; set; }
-
-        [NamedArgument('i', "int")]
-        public int IntOption { get; set; }
-
-        [NamedArgument('b', "bool", Constraint = NumArgsConstraint.Optional, Const = true)]
-        public bool BoolOption { get; set; }
-
-        public void Execute()
-        {
-        }
-    }
-}

CliFx.Benchmarks/Commands/CoconaCommand.cs

@@ -1,17 +0,0 @@
-using Cocona;
-
-namespace CliFx.Benchmarks.Commands
-{
-    public class CoconaCommand
-    {
-        public void Execute(
-            [Option("str", new []{'s'})]
-            string? strOption,
-            [Option("int", new []{'i'})]
-            int intOption,
-            [Option("bool", new []{'b'})]
-            bool boolOption)
-        {
-        }
-    }
-}

CliFx.Benchmarks/Commands/CommandLineParserCommand.cs

@@ -1,20 +0,0 @@
-using CommandLine;
-
-namespace CliFx.Benchmarks.Commands
-{
-    public class CommandLineParserCommand
-    {
-        [Option('s', "str")]
-        public string? StrOption { get; set; }
-
-        [Option('i', "int")]
-        public int IntOption { get; set; }
-
-        [Option('b', "bool")]
-        public bool BoolOption { get; set; }
-
-        public void Execute()
-        {
-        }
-    }
-}

CliFx.Benchmarks/Commands/McMasterCommand.cs

@@ -1,18 +0,0 @@
-using McMaster.Extensions.CommandLineUtils;
-
-namespace CliFx.Benchmarks.Commands
-{
-    public class McMasterCommand
-    {
-        [Option("--str|-s")]
-        public string? StrOption { get; set; }
-
-        [Option("--int|-i")]
-        public int IntOption { get; set; }
-
-        [Option("--bool|-b")]
-        public bool BoolOption { get; set; }
-
-        public int OnExecute() => 0;
-    }
-}

CliFx.Benchmarks/Commands/PowerArgsCommand.cs

@@ -1,20 +0,0 @@
-using PowerArgs;
-
-namespace CliFx.Benchmarks.Commands
-{
-    public class PowerArgsCommand
-    {
-        [ArgShortcut("--str"), ArgShortcut("-s")]
-        public string? StrOption { get; set; }
-
-        [ArgShortcut("--int"), ArgShortcut("-i")]
-        public int IntOption { get; set; }
-
-        [ArgShortcut("--bool"), ArgShortcut("-b")]
-        public bool BoolOption { get; set; }
-
-        public void Main()
-        {
-        }
-    }
-}

CliFx.Benchmarks/Commands/SystemCommandLineCommand.cs

@@ -1,34 +0,0 @@
-using System.CommandLine;
-using System.CommandLine.Invocation;
-using System.Threading.Tasks;
-
-namespace CliFx.Benchmarks.Commands
-{
-    public class SystemCommandLineCommand
-    {
-        public static int ExecuteHandler(string s, int i, bool b) => 0;
-
-        public Task<int> ExecuteAsync(string[] args)
-        {
-            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>()
-                }
-            };
-
-            command.Handler = CommandHandler.Create(typeof(SystemCommandLineCommand).GetMethod(nameof(ExecuteHandler)));
-
-            return command.InvokeAsync(args);
-        }
-    }
-}

CliFx.Benchmarks/Readme.md

@@ -0,0 +1,22 @@
+## CliFx.Benchmarks
+
+All benchmarks below were ran with the following configuration:
+
+```ini
+BenchmarkDotNet=v0.12.0, OS=Windows 10.0.14393.3443 (1607/AnniversaryUpdate/Redstone1)
+Intel Core i5-4460 CPU 3.20GHz (Haswell), 1 CPU, 4 logical and 4 physical cores
+Frequency=3124994 Hz, Resolution=320.0006 ns, Timer=TSC
+.NET Core SDK=3.1.100
+  [Host]     : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT
+  DefaultJob : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT
+```
+
+| Method                               |        Mean |     Error |     StdDev | Ratio | RatioSD | Rank |
+| ------------------------------------ | ----------: | --------: | ---------: | ----: | ------: | ---: |
+| CommandLineParser                    |    24.79 us |  0.166 us |   0.155 us |  0.49 |    0.00 |    1 |
+| CliFx                                |    50.27 us |  0.248 us |   0.232 us |  1.00 |    0.00 |    2 |
+| Clipr                                |   160.22 us |  0.817 us |   0.764 us |  3.19 |    0.02 |    3 |
+| McMaster.Extensions.CommandLineUtils |   166.45 us |  1.111 us |   1.039 us |  3.31 |    0.03 |    4 |
+| System.CommandLine                   |   170.27 us |  0.599 us |   0.560 us |  3.39 |    0.02 |    5 |
+| PowerArgs                            |   306.12 us |  1.495 us |   1.398 us |  6.09 |    0.03 |    6 |
+| Cocona                               | 1,856.07 us | 48.727 us | 141.367 us | 37.88 |    2.60 |    7 |

CliFx.Demo/CliFx.Demo.csproj

@@ -1,14 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="3.1.2" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="5.0.1" />
-    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Demo/Commands/BookAddCommand.cs

@@ -1,45 +1,45 @@
 using System;
 using System.Threading.Tasks;
 using CliFx.Attributes;
-using CliFx.Demo.Internal;
+using CliFx.Demo.Domain;
-using CliFx.Demo.Models;
+using CliFx.Demo.Utils;
-using CliFx.Demo.Services;
 using CliFx.Exceptions;
+using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands
 {
     [Command("book add", Description = "Add a book to the library.")]
     public partial class BookAddCommand : ICommand
     {
-        private readonly LibraryService _libraryService;
+        private readonly LibraryProvider _libraryProvider;
 
         [CommandParameter(0, Name = "title", Description = "Book title.")]
-        public string Title { get; set; } = "";
+        public string Title { get; init; } = "";
 
         [CommandOption("author", 'a', IsRequired = true, Description = "Book author.")]
-        public string Author { get; set; } = "";
+        public string Author { get; init; } = "";
 
         [CommandOption("published", 'p', Description = "Book publish date.")]
-        public DateTimeOffset Published { get; set; } = CreateRandomDate();
+        public DateTimeOffset Published { get; init; } = CreateRandomDate();
 
         [CommandOption("isbn", 'n', Description = "Book ISBN.")]
-        public Isbn Isbn { get; set; } = CreateRandomIsbn();
+        public Isbn Isbn { get; init; } = CreateRandomIsbn();
 
-        public BookAddCommand(LibraryService libraryService)
+        public BookAddCommand(LibraryProvider libraryProvider)
         {
-            _libraryService = libraryService;
+            _libraryProvider = libraryProvider;
         }
 
         public ValueTask ExecuteAsync(IConsole console)
         {
-            if (_libraryService.GetBook(Title) != null)
+            if (_libraryProvider.TryGetBook(Title) is not null)
-                throw new CommandException("Book already exists.", 1);
+                throw new CommandException("Book already exists.", 10);
 
             var book = new Book(Title, Author, Published, Isbn);
-            _libraryService.AddBook(book);
+            _libraryProvider.AddBook(book);
 
             console.Output.WriteLine("Book added.");
-            console.RenderBook(book);
+            console.Output.WriteBook(book);
 
             return default;
         }
@@ -47,22 +47,24 @@ namespace CliFx.Demo.Commands
 
     public partial class BookAddCommand
     {
-        private static readonly Random Random = new Random();
+        private static readonly Random Random = new();
 
-        private static DateTimeOffset CreateRandomDate() => new DateTimeOffset(
+        private static DateTimeOffset CreateRandomDate() => new(
             Random.Next(1800, 2020),
             Random.Next(1, 12),
             Random.Next(1, 28),
             Random.Next(1, 23),
             Random.Next(1, 59),
             Random.Next(1, 59),
-            TimeSpan.Zero);
+            TimeSpan.Zero
+        );
 
-        private static Isbn CreateRandomIsbn() => new Isbn(
+        private static Isbn CreateRandomIsbn() => new(
             Random.Next(0, 999),
             Random.Next(0, 99),
             Random.Next(0, 99999),
             Random.Next(0, 99),
-            Random.Next(0, 9));
+            Random.Next(0, 9)
+        );
     }
 }

CliFx.Demo/Commands/BookCommand.cs

@@ -1,32 +1,33 @@
 using System.Threading.Tasks;
 using CliFx.Attributes;
-using CliFx.Demo.Internal;
+using CliFx.Demo.Domain;
-using CliFx.Demo.Services;
+using CliFx.Demo.Utils;
 using CliFx.Exceptions;
+using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands
 {
-    [Command("book", Description = "View, list, add or remove books.")]
+    [Command("book", Description = "Retrieve a book from the library.")]
     public class BookCommand : ICommand
     {
-        private readonly LibraryService _libraryService;
+        private readonly LibraryProvider _libraryProvider;
 
-        [CommandParameter(0, Name = "title", Description = "Book title.")]
+        [CommandParameter(0, Name = "title", Description = "Title of the book to retrieve.")]
-        public string Title { get; set; } = "";
+        public string Title { get; init; } = "";
 
-        public BookCommand(LibraryService libraryService)
+        public BookCommand(LibraryProvider libraryProvider)
         {
-            _libraryService = libraryService;
+            _libraryProvider = libraryProvider;
         }
 
         public ValueTask ExecuteAsync(IConsole console)
         {
-            var book = _libraryService.GetBook(Title);
+            var book = _libraryProvider.TryGetBook(Title);
 
-            if (book == null)
+            if (book is null)
-                throw new CommandException("Book not found.", 1);
+                throw new CommandException("Book not found.", 10);
 
-            console.RenderBook(book);
+            console.Output.WriteBook(book);
 
             return default;
         }

CliFx.Demo/Commands/BookListCommand.cs

@@ -1,34 +1,34 @@
 using System.Threading.Tasks;
 using CliFx.Attributes;
-using CliFx.Demo.Internal;
+using CliFx.Demo.Domain;
-using CliFx.Demo.Services;
+using CliFx.Demo.Utils;
+using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands
 {
     [Command("book list", Description = "List all books in the library.")]
     public class BookListCommand : ICommand
     {
-        private readonly LibraryService _libraryService;
+        private readonly LibraryProvider _libraryProvider;
 
-        public BookListCommand(LibraryService libraryService)
+        public BookListCommand(LibraryProvider libraryProvider)
         {
-            _libraryService = libraryService;
+            _libraryProvider = libraryProvider;
         }
 
         public ValueTask ExecuteAsync(IConsole console)
         {
-            var library = _libraryService.GetLibrary();
+            var library = _libraryProvider.GetLibrary();
 
-            var isFirst = true;
+            for (var i = 0; i < library.Books.Count; i++)
-            foreach (var book in library.Books)
             {
-                // Margin
+                // Add margin
-                if (!isFirst)
+                if (i != 0)
                     console.Output.WriteLine();
-                isFirst = false;
 
                 // Render book
-                console.RenderBook(book);
+                var book = library.Books[i];
+                console.Output.WriteBook(book);
             }
 
             return default;

CliFx.Demo/Commands/BookRemoveCommand.cs

@@ -1,31 +1,32 @@
 using System.Threading.Tasks;
 using CliFx.Attributes;
-using CliFx.Demo.Services;
+using CliFx.Demo.Domain;
 using CliFx.Exceptions;
+using CliFx.Infrastructure;
 
 namespace CliFx.Demo.Commands
 {
     [Command("book remove", Description = "Remove a book from the library.")]
     public class BookRemoveCommand : ICommand
     {
-        private readonly LibraryService _libraryService;
+        private readonly LibraryProvider _libraryProvider;
 
-        [CommandParameter(0, Name = "title", Description = "Book title.")]
+        [CommandParameter(0, Name = "title", Description = "Title of the book to remove.")]
-        public string Title { get; set; } = "";
+        public string Title { get; init; } = "";
 
-        public BookRemoveCommand(LibraryService libraryService)
+        public BookRemoveCommand(LibraryProvider libraryProvider)
         {
-            _libraryService = libraryService;
+            _libraryProvider = libraryProvider;
         }
 
         public ValueTask ExecuteAsync(IConsole console)
         {
-            var book = _libraryService.GetBook(Title);
+            var book = _libraryProvider.TryGetBook(Title);
 
-            if (book == null)
+            if (book is null)
-                throw new CommandException("Book not found.", 1);
+                throw new CommandException("Book not found.", 10);
 
-            _libraryService.RemoveBook(book);
+            _libraryProvider.RemoveBook(book);
 
             console.Output.WriteLine($"Book {Title} removed.");
 

CliFx.Demo/Domain/Book.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace CliFx.Demo.Models
+namespace CliFx.Demo.Domain
 {
     public class Book
     {

CliFx.Demo/Domain/Isbn.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace CliFx.Demo.Models
+namespace CliFx.Demo.Domain
 {
     public partial class Isbn
     {

CliFx.Demo/Domain/Library.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace CliFx.Demo.Domain
+{
+    public partial class Library
+    {
+        public IReadOnlyList<Book> Books { get; }
+
+        public Library(IReadOnlyList<Book> books)
+        {
+            Books = books;
+        }
+
+        public Library WithBook(Book book)
+        {
+            var books = Books.ToList();
+            books.Add(book);
+
+            return new Library(books);
+        }
+
+        public Library WithoutBook(Book book)
+        {
+            var books = Books.Where(b => b != book).ToArray();
+
+            return new Library(books);
+        }
+    }
+
+    public partial class Library
+    {
+        public static Library Empty { get; } = new(Array.Empty<Book>());
+    }
+}

CliFx.Demo/Domain/LibraryProvider.cs

@@ -1,13 +1,12 @@
 using System.IO;
 using System.Linq;
-using CliFx.Demo.Models;
 using Newtonsoft.Json;
 
-namespace CliFx.Demo.Services
+namespace CliFx.Demo.Domain
 {
-    public class LibraryService
+    public class LibraryProvider
     {
-        private string StorageFilePath => Path.Combine(Directory.GetCurrentDirectory(), "Data.json");
+        private static string StorageFilePath { get; } = Path.Combine(Directory.GetCurrentDirectory(), "Library.json");
 
         private void StoreLibrary(Library library)
         {
@@ -22,10 +21,10 @@ namespace CliFx.Demo.Services
 
             var data = File.ReadAllText(StorageFilePath);
 
-            return JsonConvert.DeserializeObject<Library>(data);
+            return JsonConvert.DeserializeObject<Library>(data) ?? Library.Empty;
         }
 
-        public Book? GetBook(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/Internal/Extensions.cs

@@ -1,29 +0,0 @@
-using System;
-using CliFx.Demo.Models;
-
-namespace CliFx.Demo.Internal
-{
-    internal static class Extensions
-    {
-        public static void RenderBook(this IConsole console, Book book)
-        {
-            // Title
-            console.WithForegroundColor(ConsoleColor.White, () => console.Output.WriteLine(book.Title));
-
-            // Author
-            console.Output.Write("  ");
-            console.Output.Write("Author: ");
-            console.WithForegroundColor(ConsoleColor.White, () => console.Output.WriteLine(book.Author));
-
-            // Published
-            console.Output.Write("  ");
-            console.Output.Write("Published: ");
-            console.WithForegroundColor(ConsoleColor.White, () => console.Output.WriteLine($"{book.Published:d}"));
-
-            // ISBN
-            console.Output.Write("  ");
-            console.Output.Write("ISBN: ");
-            console.WithForegroundColor(ConsoleColor.White, () => console.Output.WriteLine(book.Isbn));
-        }
-    }
-}

CliFx.Demo/Models/Extensions.cs

@@ -1,22 +0,0 @@
-using System.Linq;
-
-namespace CliFx.Demo.Models
-{
-    public static class Extensions
-    {
-        public static Library WithBook(this Library library, Book book)
-        {
-            var books = library.Books.ToList();
-            books.Add(book);
-
-            return new Library(books);
-        }
-
-        public static Library WithoutBook(this Library library, Book book)
-        {
-            var books = library.Books.Where(b => b != book).ToArray();
-
-            return new Library(books);
-        }
-    }
-}

CliFx.Demo/Models/Library.cs

@@ -1,20 +0,0 @@
-using System;
-using System.Collections.Generic;
-
-namespace CliFx.Demo.Models
-{
-    public partial class Library
-    {
-        public IReadOnlyList<Book> Books { get; }
-
-        public Library(IReadOnlyList<Book> books)
-        {
-            Books = books;
-        }
-    }
-
-    public partial class Library
-    {
-        public static Library Empty { get; } = new Library(Array.Empty<Book>());
-    }
-}

CliFx.Demo/Program.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Threading.Tasks;
 using CliFx.Demo.Commands;
-using CliFx.Demo.Services;
+using CliFx.Demo.Domain;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace CliFx.Demo
@@ -14,7 +14,7 @@ namespace CliFx.Demo
             var services = new ServiceCollection();
 
             // Register services
-            services.AddSingleton<LibraryService>();
+            services.AddSingleton<LibraryProvider>();
 
             // Register commands
             services.AddTransient<BookCommand>();
@@ -27,8 +27,9 @@ namespace CliFx.Demo
 
         public static async Task<int> Main() =>
             await new CliApplicationBuilder()
+                .SetDescription("Demo application showcasing CliFx features.")
                 .AddCommandsFromThisAssembly()
-                .UseTypeActivator(GetServiceProvider().GetService)
+                .UseTypeActivator(GetServiceProvider().GetRequiredService)
                 .Build()
                 .RunAsync();
     }

CliFx.Demo/Readme.md

@@ -2,6 +2,4 @@
 
 Sample command line interface for managing a library of books.
 
-This demo project shows basic CliFx functionality such as command routing, argument parsing, autogenerated help text, and some other things.
+This demo project showcases basic CliFx functionality such as command routing, argument parsing, autogenerated help text.
-
-You can get a list of available commands by running `CliFx.Demo --help`.

CliFx.Demo/Utils/ConsoleExtensions.cs

@@ -0,0 +1,37 @@
+using System;
+using CliFx.Demo.Domain;
+using CliFx.Infrastructure;
+
+namespace CliFx.Demo.Utils
+{
+    internal static class ConsoleExtensions
+    {
+        public static void WriteBook(this ConsoleWriter writer, Book book)
+        {
+            // Title
+            using (writer.Console.WithForegroundColor(ConsoleColor.White))
+                writer.WriteLine(book.Title);
+
+            // Author
+            writer.Write("  ");
+            writer.Write("Author: ");
+
+            using (writer.Console.WithForegroundColor(ConsoleColor.White))
+                writer.WriteLine(book.Author);
+
+            // Published
+            writer.Write("  ");
+            writer.Write("Published: ");
+
+            using (writer.Console.WithForegroundColor(ConsoleColor.White))
+                writer.WriteLine($"{book.Published:d}");
+
+            // ISBN
+            writer.Write("  ");
+            writer.Write("ISBN: ");
+
+            using (writer.Console.WithForegroundColor(ConsoleColor.White))
+                writer.WriteLine(book.Isbn);
+        }
+    }
+}

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

@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

CliFx.Tests.Dummy/Commands/ConsoleTestCommand.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Threading.Tasks;
 using CliFx.Attributes;
+using CliFx.Infrastructure;
 
 namespace CliFx.Tests.Dummy.Commands
 {
@@ -11,11 +12,11 @@ namespace CliFx.Tests.Dummy.Commands
         {
             var input = console.Input.ReadToEnd();
 
-            console.WithColors(ConsoleColor.Black, ConsoleColor.White, () =>
+            using (console.WithColors(ConsoleColor.Black, ConsoleColor.White))
             {
                 console.Output.WriteLine(input);
                 console.Error.WriteLine(input);
-            });
+            }
 
             return default;
         }

CliFx.Tests.Dummy/Commands/EnvironmentTestCommand.cs

@@ -0,0 +1,20 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Tests.Dummy.Commands
+{
+    [Command("env-test")]
+    public class EnvironmentTestCommand : ICommand
+    {
+        [CommandOption("target", EnvironmentVariable = "ENV_TARGET")]
+        public string GreetingTarget { get; set; } = "World";
+
+        public ValueTask ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine($"Hello {GreetingTarget}!");
+
+            return default;
+        }
+    }
+}