Update version

Closes #103

Changelog.md

@@ -1,3 +1,25 @@
+### v2.2.3 (17-Apr-2022)
+
+- Changed method signature of `IConsole.ReadKey()` to return `ConsoleKeyInfo` instead of `void`. The return type was originally defined as `void` by mistake. This change is source-backwards-compatible but may break on binary level if you were previously calling this method indirectly (i.e. through a library).
+- Added `FakeConsole.EnqueueKey(...)` to facilitate the testing of `IConsole.ReadKey()`. You can use this method to simulate key presses in your application.
+- Extended analyzers that verify the correctness of specified converters and validators. They now also ensure that the specified types are compatible with the type of the underlying property.
+- Improved diagnostics produced by analyzers. Where relevant, highlighted code is now limited to the property or type identifier, instead of the whole property or type declaration. Also extended the diagnostic messages with additional information.
+- Fixed an issue where throwing an exception inside a constructor of a command type resulted in an unrelated error message about the absence of a parameterless constructor.
+
+### v2.2.2 (30-Jan-2022)
+
+- Fixed an issue where `ConsoleWriter` and `ConsoleReader` were not properly thread-safe.
+- Fixed an issue where the analyzer failed to load under certain circumstances when running inside Visual Studio.
+
+### v2.2.1 (16-Jan-2022)
+
+- Fixed an issue which caused help text to not show default values for optional parameters. (Thanks [@AliReZa Sabouri](https://github.com/alirezanet))
+
+### v2.2 (11-Jan-2022)
+
+- Added support for optional parameters. A parameter can be marked as optional by setting `IsRequired = false` on the attribute. Only one parameter is allowed to be optional and such parameter must be the last in order. (Thanks [@AliReZa Sabouri](https://github.com/alirezanet))
+- Fixed an issue where parameters and options bound to properties implemented as default interface members were not working correctly. (Thanks [@AliReZa Sabouri](https://github.com/alirezanet))
+
 ### v2.1 (04-Jan-2022)
 
 - Added `IConsole.Clear()` with corresponding implementations in `SystemConsole`, `FakeConsole`, and `FakeInMemoryConsole`. (Thanks [@Alex Rosenfeld](https://github.com/alexrosenfeld10))
@@ -37,7 +59,7 @@
 ### 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.
+> 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.

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

@@ -2,10 +2,6 @@
 
   <PropertyGroup>
     <TargetFramework>net6.0</TargetFramework>
-    <IsPackable>false</IsPackable>
-    <IsTestProject>true</IsTestProject>
-    <CollectCoverage>true</CollectCoverage>
-    <CoverletOutputFormat>opencover</CoverletOutputFormat>
   </PropertyGroup>
 
   <ItemGroup>
@@ -14,13 +10,13 @@
 
   <ItemGroup>
     <PackageReference Include="Basic.Reference.Assemblies" Version="1.2.4" />
-    <PackageReference Include="GitHubActionsTestLogger" Version="1.2.0" />
+    <PackageReference Include="GitHubActionsTestLogger" Version="1.3.0" PrivateAssets="all" />
-    <PackageReference Include="FluentAssertions" Version="6.2.0" />
+    <PackageReference Include="FluentAssertions" Version="6.5.1" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.0.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.1.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" PrivateAssets="all" />
-    <PackageReference Include="coverlet.msbuild" Version="3.1.0" PrivateAssets="all" />
+    <PackageReference Include="coverlet.collector" Version="3.1.2" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Analyzers.Tests/OptionMustHaveValidConverterAnalyzerSpecs.cs

@@ -33,7 +33,31 @@ public class MyCommand : ICommand
     }
 
     [Fact]
-    public void Analyzer_does_not_report_an_error_if_the_specified_option_converter_derives_from_BindingConverter()
+    public void Analyzer_reports_an_error_if_the_specified_option_converter_does_not_derive_from_a_compatible_BindingConverter()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+public class MyConverter : BindingConverter<int>
+{
+    public override int Convert(string rawValue) => 42;
+}
+
+[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_a_compatible_BindingConverter()
     {
         // Arrange
         // language=cs

CliFx.Analyzers.Tests/OptionMustHaveValidValidatorsAnalyzerSpecs.cs

@@ -33,7 +33,31 @@ public class MyCommand : ICommand
     }
 
     [Fact]
-    public void Analyzer_does_not_report_an_error_if_all_specified_option_validators_derive_from_BindingValidator()
+    public void Analyzer_reports_an_error_if_one_of_the_specified_option_validators_does_not_derive_from_a_compatible_BindingValidator()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+public class MyValidator : BindingValidator<int>
+{
+    public override BindingValidationError Validate(int 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().ProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_each_specified_option_validator_derives_from_a_compatible_BindingValidator()
     {
         // Arrange
         // language=cs

CliFx.Analyzers.Tests/ParameterMustBeLastIfNonRequiredAnalyzerSpecs.cs

@@ -0,0 +1,94 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests;
+
+public class ParameterMustBeLastIfNonRequiredAnalyzerSpecs
+{
+    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeLastIfNonRequiredAnalyzer();
+
+    [Fact]
+    public void Analyzer_reports_an_error_if_a_non_required_parameter_is_not_the_last_in_order()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"", IsRequired = false)]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, Name = ""bar"")]
+    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_required_parameter_is_the_last_in_order()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"")]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, Name = ""bar"", IsRequired = false)]
+    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_required_parameters_are_defined()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"")]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, Name = ""bar"", IsRequired = true)]
+    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/ParameterMustBeLastIfNonScalarAnalyzerSpecs.cs

@@ -9,7 +9,7 @@ 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()
+    public void Analyzer_reports_an_error_if_a_non_scalar_parameter_is_not_the_last_in_order()
     {
         // Arrange
         // language=cs
@@ -31,7 +31,7 @@ public class MyCommand : ICommand
     }
 
     [Fact]
-    public void Analyzer_does_not_report_an_error_if_a_non_scalar_parameter_is_last_in_order()
+    public void Analyzer_does_not_report_an_error_if_a_non_scalar_parameter_is_the_last_in_order()
     {
         // Arrange
         // language=cs

CliFx.Analyzers.Tests/ParameterMustBeSingleIfNonRequiredAnalyzerSpecs.cs

@@ -0,0 +1,94 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests;
+
+public class ParameterMustBeSingleIfNonRequiredAnalyzerSpecs
+{
+    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeSingleIfNonRequiredAnalyzer();
+
+    [Fact]
+    public void Analyzer_reports_an_error_if_more_than_one_non_required_parameters_are_defined()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, IsRequired = false)]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, IsRequired = false)]
+    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_required_parameter_is_defined()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, IsRequired = false)]
+    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_required_parameters_are_defined()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, IsRequired = true)]
+    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

@@ -33,7 +33,32 @@ public class MyCommand : ICommand
     }
 
     [Fact]
-    public void Analyzer_does_not_report_an_error_if_the_specified_parameter_converter_derives_from_BindingConverter()
+    public void Analyzer_reports_an_error_if_the_specified_parameter_converter_does_not_derive_from_a_compatible_BindingConverter()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+public class MyConverter : BindingConverter<int>
+{
+    public override int Convert(string rawValue) => 42;
+}
+
+[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_a_compatible_BindingConverter()
     {
         // Arrange
         // language=cs

CliFx.Analyzers.Tests/ParameterMustHaveValidValidatorsAnalyzerSpecs.cs

@@ -33,7 +33,31 @@ public class MyCommand : ICommand
     }
 
     [Fact]
-    public void Analyzer_does_not_report_an_error_if_all_specified_parameter_validators_derive_from_BindingValidator()
+    public void Analyzer_reports_an_error_if_one_of_the_specified_parameter_validators_does_not_derive_from_a_compatible_BindingValidator()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+public class MyValidator : BindingValidator<int>
+{
+    public override BindingValidationError Validate(int 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().ProduceDiagnostics(code);
+    }
+
+    [Fact]
+    public void Analyzer_does_not_report_an_error_if_each_specified_parameter_validator_derives_from_a_compatible_BindingValidator()
     {
         // Arrange
         // language=cs

CliFx.Analyzers.Tests/Utils/AnalyzerAssertions.cs

@@ -57,7 +57,7 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
         // Compile the code to IL
         var compilation = CSharpCompilation.Create(
             "CliFxTests_DynamicAssembly_" + Guid.NewGuid(),
-            new[] {ast},
+            new[] { ast },
             ReferenceAssemblies.Net50
                 .Append(MetadataReference.CreateFromFile(typeof(ICommand).Assembly.Location)),
             // DLL to avoid having to define the Main() method
@@ -101,11 +101,11 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
         var expectedDiagnosticIds = expectedDiagnostics.Select(d => d.Id).Distinct().ToArray();
         var producedDiagnosticIds = producedDiagnostics.Select(d => d.Id).Distinct().ToArray();
 
-        var result =
+        var isSuccessfulAssertion =
             expectedDiagnosticIds.Intersect(producedDiagnosticIds).Count() ==
             expectedDiagnosticIds.Length;
 
-        Execute.Assertion.ForCondition(result).FailWith(() =>
+        Execute.Assertion.ForCondition(isSuccessfulAssertion).FailWith(() =>
         {
             var buffer = new StringBuilder();
 
@@ -125,11 +125,18 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
 
             buffer.AppendLine("Produced diagnostics:");
 
+            if (producedDiagnostics.Any())
+            {
                 foreach (var producedDiagnostic in producedDiagnostics)
                 {
                     buffer.Append("  - ");
                     buffer.Append(producedDiagnostic);
                 }
+            }
+            else
+            {
+                buffer.AppendLine("  < none >");
+            }
 
             return new FailReason(buffer.ToString());
         });
@@ -138,10 +145,9 @@ internal class AnalyzerAssertions : ReferenceTypeAssertions<DiagnosticAnalyzer,
     public void NotProduceDiagnostics(string sourceCode)
     {
         var producedDiagnostics = GetProducedDiagnostics(sourceCode);
+        var isSuccessfulAssertion = !producedDiagnostics.Any();
 
-        var result = !producedDiagnostics.Any();
+        Execute.Assertion.ForCondition(isSuccessfulAssertion).FailWith(() =>
-
-        Execute.Assertion.ForCondition(result).FailWith(() =>
         {
             var buffer = new StringBuilder();
 

CliFx.Analyzers/AnalyzerBase.cs

@@ -28,8 +28,8 @@ public abstract class AnalyzerBase : DiagnosticAnalyzer
         SupportedDiagnostics = ImmutableArray.Create(SupportedDiagnostic);
     }
 
-    protected Diagnostic CreateDiagnostic(Location location) =>
+    protected Diagnostic CreateDiagnostic(Location location, params object?[]? messageArgs) =>
-        Diagnostic.Create(SupportedDiagnostic, location);
+        Diagnostic.Create(SupportedDiagnostic, location, messageArgs);
 
     public override void Initialize(AnalysisContext context)
     {

CliFx.Analyzers/CliFx.Analyzers.csproj

@@ -2,12 +2,13 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
     <Nullable>annotations</Nullable>
     <NoWarn>$(NoWarn);RS1025;RS1026</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.4.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.1.0" PrivateAssets="all" />
   </ItemGroup>
 
 </Project>

CliFx.Analyzers/CommandMustBeAnnotatedAnalyzer.cs

@@ -30,18 +30,20 @@ public class CommandMustBeAnnotatedAnalyzer : AnalyzerBase
 
         var implementsCommandInterface = type
             .AllInterfaces
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+            .Any(i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
 
         var hasCommandAttribute = type
             .GetAttributes()
             .Select(a => a.AttributeClass)
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
+            .Any(c => c.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()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(classDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/CommandMustImplementInterfaceAnalyzer.cs

@@ -25,17 +25,19 @@ public class CommandMustImplementInterfaceAnalyzer : AnalyzerBase
         var hasCommandAttribute = type
             .GetAttributes()
             .Select(a => a.AttributeClass)
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
+            .Any(c => c.DisplayNameMatches(SymbolNames.CliFxCommandAttribute));
 
         var implementsCommandInterface = type
             .AllInterfaces
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+            .Any(i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
 
         // If the attribute is present, but the interface is not implemented,
         // it's very likely a user error.
         if (hasCommandAttribute && !implementsCommandInterface)
         {
-            context.ReportDiagnostic(CreateDiagnostic(classDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(classDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/ObjectModel/CommandOptionSymbol.cs

@@ -1,7 +1,7 @@
 using System.Collections.Generic;
-using Microsoft.CodeAnalysis;
 using System.Linq;
 using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
 
 namespace CliFx.Analyzers.ObjectModel;
 
@@ -71,10 +71,9 @@ internal partial class CommandOptionSymbol
     {
         var attribute = TryGetOptionAttribute(property);
 
-        if (attribute is null)
+        return attribute is not null
-            return null;
+            ? FromAttribute(attribute)
-
+            : null;
-        return FromAttribute(attribute);
     }
 
     public static bool IsOptionProperty(IPropertySymbol property) =>

CliFx.Analyzers/ObjectModel/CommandParameterSymbol.cs

@@ -11,6 +11,8 @@ internal partial class CommandParameterSymbol
 
     public string? Name { get; }
 
+    public bool? IsRequired { get; }
+
     public ITypeSymbol? ConverterType { get; }
 
     public IReadOnlyList<ITypeSymbol> ValidatorTypes { get; }
@@ -18,11 +20,13 @@ internal partial class CommandParameterSymbol
     public CommandParameterSymbol(
         int order,
         string? name,
+        bool? isRequired,
         ITypeSymbol? converterType,
         IReadOnlyList<ITypeSymbol> validatorTypes)
     {
         Order = order;
         Name = name;
+        IsRequired = isRequired;
         ConverterType = converterType;
         ValidatorTypes = validatorTypes;
     }
@@ -37,7 +41,7 @@ internal partial class CommandParameterSymbol
 
     private static CommandParameterSymbol FromAttribute(AttributeData attribute)
     {
-        var order = (int) attribute
+        var order = (int)attribute
             .ConstructorArguments
             .Select(a => a.Value)
             .First()!;
@@ -48,6 +52,12 @@ internal partial class CommandParameterSymbol
             .Select(a => a.Value.Value)
             .FirstOrDefault() as string;
 
+        var isRequired = attribute
+            .NamedArguments
+            .Where(a => a.Key == "IsRequired")
+            .Select(a => a.Value.Value)
+            .FirstOrDefault() as bool?;
+
         var converter = attribute
             .NamedArguments
             .Where(a => a.Key == "Converter")
@@ -63,17 +73,16 @@ internal partial class CommandParameterSymbol
             .Cast<ITypeSymbol>()
             .ToArray();
 
-        return new CommandParameterSymbol(order, name, converter, validators);
+        return new CommandParameterSymbol(order, name, isRequired, converter, validators);
     }
 
     public static CommandParameterSymbol? TryResolve(IPropertySymbol property)
     {
         var attribute = TryGetParameterAttribute(property);
 
-        if (attribute is null)
+        return attribute is not null
-            return null;
+            ? FromAttribute(attribute)
-
+            : null;
-        return FromAttribute(attribute);
     }
 
     public static bool IsParameterProperty(IPropertySymbol property) =>

CliFx.Analyzers/ObjectModel/SymbolNames.cs

@@ -7,8 +7,6 @@ internal static class SymbolNames
     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

@@ -34,11 +34,13 @@ public class OptionMustBeInsideCommandAnalyzer : AnalyzerBase
         var isInsideCommand = property
             .ContainingType
             .AllInterfaces
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+            .Any(i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
 
         if (!isInsideCommand)
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/OptionMustHaveNameOrShortNameAnalyzer.cs

@@ -27,7 +27,9 @@ public class OptionMustHaveNameOrShortNameAnalyzer : AnalyzerBase
 
         if (string.IsNullOrWhiteSpace(option.Name) && option.ShortName is null)
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/OptionMustHaveUniqueNameAnalyzer.cs

@@ -14,7 +14,8 @@ 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).")
+            "This option's name must be unique within the command (comparison IS NOT case sensitive). " +
+            "Specified name: '{0}'.")
     {
     }
 
@@ -51,7 +52,12 @@ public class OptionMustHaveUniqueNameAnalyzer : AnalyzerBase
 
             if (string.Equals(option.Name, otherOption.Name, StringComparison.OrdinalIgnoreCase))
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(
+                        propertyDeclaration.Identifier.GetLocation(),
+                        option.Name
+                    )
+                );
             }
         }
     }

CliFx.Analyzers/OptionMustHaveUniqueShortNameAnalyzer.cs

@@ -13,7 +13,8 @@ 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).")
+            "This option's short name must be unique within the command (comparison IS case sensitive). " +
+            "Specified short name: '{0}'.")
     {
     }
 
@@ -50,7 +51,12 @@ public class OptionMustHaveUniqueShortNameAnalyzer : AnalyzerBase
 
             if (option.ShortName == otherOption.ShortName)
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(
+                        propertyDeclaration.Identifier.GetLocation(),
+                        option.ShortName
+                    )
+                );
             }
         }
     }

CliFx.Analyzers/OptionMustHaveValidConverterAnalyzer.cs

@@ -13,7 +13,7 @@ public class OptionMustHaveValidConverterAnalyzer : AnalyzerBase
     public OptionMustHaveValidConverterAnalyzer()
         : base(
             $"Option converters must derive from `{SymbolNames.CliFxBindingConverterClass}`",
-            $"Converter specified for this option must derive from `{SymbolNames.CliFxBindingConverterClass}`.")
+            $"Converter specified for this option must derive from a compatible `{SymbolNames.CliFxBindingConverterClass}`.")
     {
     }
 
@@ -29,15 +29,19 @@ public class OptionMustHaveValidConverterAnalyzer : AnalyzerBase
         if (option.ConverterType is null)
             return;
 
-        // We check against an internal interface because checking against a generic class is a pain
+        var converterValueType = option
-        var converterImplementsInterface = option
             .ConverterType
-            .AllInterfaces
+            .GetBaseTypes()
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingConverterInterface));
+            .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingConverterClass))?
+            .TypeArguments
+            .FirstOrDefault();
 
-        if (!converterImplementsInterface)
+        // Value returned by the converter must be assignable to the property type
+        if (converterValueType is null || !property.Type.IsAssignableFrom(converterValueType))
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/OptionMustHaveValidNameAnalyzer.cs

@@ -12,7 +12,8 @@ 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.")
+            "This option's name must be at least 2 characters long and must start with a letter. " +
+            "Specified name: '{0}'.")
     {
     }
 
@@ -30,7 +31,12 @@ public class OptionMustHaveValidNameAnalyzer : AnalyzerBase
 
         if (option.Name.Length < 2 || !char.IsLetter(option.Name[0]))
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(
+                    propertyDeclaration.Identifier.GetLocation(),
+                    option.Name
+                )
+            );
         }
     }
 

CliFx.Analyzers/OptionMustHaveValidShortNameAnalyzer.cs

@@ -12,7 +12,8 @@ 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.")
+            "This option's short name must be a single letter character. " +
+            "Specified short name: '{0}'.")
     {
     }
 
@@ -30,7 +31,12 @@ public class OptionMustHaveValidShortNameAnalyzer : AnalyzerBase
 
         if (!char.IsLetter(option.ShortName.Value))
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(
+                    propertyDeclaration.Identifier.GetLocation(),
+                    option.ShortName
+                )
+            );
         }
     }
 

CliFx.Analyzers/OptionMustHaveValidValidatorsAnalyzer.cs

@@ -13,7 +13,7 @@ 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}`.")
+            $"Each validator specified for this option must derive from a compatible `{SymbolNames.CliFxBindingValidatorClass}`.")
     {
     }
 
@@ -28,14 +28,18 @@ public class OptionMustHaveValidValidatorsAnalyzer : AnalyzerBase
 
         foreach (var validatorType in option.ValidatorTypes)
         {
-            // We check against an internal interface because checking against a generic class is a pain
+            var validatorValueType = validatorType
-            var validatorImplementsInterface = validatorType
+                .GetBaseTypes()
-                .AllInterfaces
+                .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingValidatorClass))?
-                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingValidatorInterface));
+                .TypeArguments
+                .FirstOrDefault();
 
-            if (!validatorImplementsInterface)
+            // Value passed to the validator must be assignable from the property type
+            if (validatorValueType is null || !validatorValueType.IsAssignableFrom(property.Type))
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+                );
 
                 // No need to report multiple identical diagnostics on the same node
                 break;

CliFx.Analyzers/ParameterMustBeInsideCommandAnalyzer.cs

@@ -34,11 +34,13 @@ public class ParameterMustBeInsideCommandAnalyzer : AnalyzerBase
         var isInsideCommand = property
             .ContainingType
             .AllInterfaces
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
+            .Any(i => i.DisplayNameMatches(SymbolNames.CliFxCommandInterface));
 
         if (!isInsideCommand)
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/ParameterMustBeLastIfNonRequiredAnalyzer.cs

@@ -0,0 +1,62 @@
+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 ParameterMustBeLastIfNonRequiredAnalyzer : AnalyzerBase
+{
+    public ParameterMustBeLastIfNonRequiredAnalyzer()
+        : base(
+            "Parameters marked as non-required must be the last in order",
+            "This parameter is non-required so it must be the last in order (its order must be highest within the command).")
+    {
+    }
+
+    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 (parameter.IsRequired != false)
+            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.Identifier.GetLocation())
+                );
+            }
+        }
+    }
+
+    public override void Initialize(AnalysisContext context)
+    {
+        base.Initialize(context);
+        context.HandlePropertyDeclaration(Analyze);
+    }
+}

CliFx.Analyzers/ParameterMustBeLastIfNonScalarAnalyzer.cs

@@ -12,8 +12,8 @@ public class ParameterMustBeLastIfNonScalarAnalyzer : AnalyzerBase
 {
     public ParameterMustBeLastIfNonScalarAnalyzer()
         : base(
-            "Parameters of non-scalar types must be last in order",
+            "Parameters of non-scalar types must be the 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).")
+            "This parameter has a non-scalar type so it must be the last in order (its order must be highest within the command).")
     {
     }
 
@@ -22,7 +22,7 @@ public class ParameterMustBeLastIfNonScalarAnalyzer : AnalyzerBase
         type.DisplayNameMatches("System.String") ||
         !type.AllInterfaces
             .Select(i => i.ConstructedFrom)
-            .Any(s => s.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));
+            .Any(t => t.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
@@ -54,7 +54,9 @@ public class ParameterMustBeLastIfNonScalarAnalyzer : AnalyzerBase
 
             if (otherParameter.Order > parameter.Order)
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+                );
             }
         }
     }

CliFx.Analyzers/ParameterMustBeSingleIfNonRequiredAnalyzer.cs

@@ -0,0 +1,62 @@
+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 ParameterMustBeSingleIfNonRequiredAnalyzer : AnalyzerBase
+{
+    public ParameterMustBeSingleIfNonRequiredAnalyzer()
+        : base(
+            "Parameters marked as non-required are limited to one per command",
+            "This parameter is non-required so it must be the only such parameter in the command.")
+    {
+    }
+
+    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 (parameter.IsRequired != false)
+            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.IsRequired == false)
+            {
+                context.ReportDiagnostic(
+                    CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+                );
+            }
+        }
+    }
+
+    public override void Initialize(AnalysisContext context)
+    {
+        base.Initialize(context);
+        context.HandlePropertyDeclaration(Analyze);
+    }
+}

CliFx.Analyzers/ParameterMustBeSingleIfNonScalarAnalyzer.cs

@@ -22,7 +22,7 @@ public class ParameterMustBeSingleIfNonScalarAnalyzer : AnalyzerBase
         type.DisplayNameMatches("System.String") ||
         !type.AllInterfaces
             .Select(i => i.ConstructedFrom)
-            .Any(s => s.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));
+            .Any(t => t.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));
 
     private void Analyze(
         SyntaxNodeAnalysisContext context,
@@ -52,7 +52,9 @@ public class ParameterMustBeSingleIfNonScalarAnalyzer : AnalyzerBase
 
             if (!IsScalar(otherProperty.Type))
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+                );
             }
         }
     }

CliFx.Analyzers/ParameterMustHaveUniqueNameAnalyzer.cs

@@ -14,7 +14,8 @@ 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).")
+            "This parameter's name must be unique within the command (comparison IS NOT case sensitive). " +
+            "Specified name: '{0}'.")
     {
     }
 
@@ -51,7 +52,12 @@ public class ParameterMustHaveUniqueNameAnalyzer : AnalyzerBase
 
             if (string.Equals(parameter.Name, otherParameter.Name, StringComparison.OrdinalIgnoreCase))
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(
+                        propertyDeclaration.Identifier.GetLocation(),
+                        parameter.Name
+                    )
+                );
             }
         }
     }

CliFx.Analyzers/ParameterMustHaveUniqueOrderAnalyzer.cs

@@ -13,7 +13,8 @@ public class ParameterMustHaveUniqueOrderAnalyzer : AnalyzerBase
     public ParameterMustHaveUniqueOrderAnalyzer()
         : base(
             "Parameters must have unique order",
-            "This parameter's order must be unique within the command.")
+            "This parameter's order must be unique within the command. " +
+            "Specified order: {0}.")
     {
     }
 
@@ -44,7 +45,12 @@ public class ParameterMustHaveUniqueOrderAnalyzer : AnalyzerBase
 
             if (parameter.Order == otherParameter.Order)
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(
+                        propertyDeclaration.Identifier.GetLocation(),
+                        parameter.Order
+                    )
+                );
             }
         }
     }

CliFx.Analyzers/ParameterMustHaveValidConverterAnalyzer.cs

@@ -13,7 +13,7 @@ public class ParameterMustHaveValidConverterAnalyzer : AnalyzerBase
     public ParameterMustHaveValidConverterAnalyzer()
         : base(
             $"Parameter converters must derive from `{SymbolNames.CliFxBindingConverterClass}`",
-            $"Converter specified for this parameter must derive from `{SymbolNames.CliFxBindingConverterClass}`.")
+            $"Converter specified for this parameter must derive from a compatible `{SymbolNames.CliFxBindingConverterClass}`.")
     {
     }
 
@@ -29,15 +29,19 @@ public class ParameterMustHaveValidConverterAnalyzer : AnalyzerBase
         if (parameter.ConverterType is null)
             return;
 
-        // We check against an internal interface because checking against a generic class is a pain
+        var converterValueType = parameter
-        var converterImplementsInterface = parameter
             .ConverterType
-            .AllInterfaces
+            .GetBaseTypes()
-            .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingConverterInterface));
+            .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingConverterClass))?
+            .TypeArguments
+            .FirstOrDefault();
 
-        if (!converterImplementsInterface)
+        // Value returned by the converter must be assignable to the property type
+        if (converterValueType is null || !property.Type.IsAssignableFrom(converterValueType))
         {
-            context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/ParameterMustHaveValidValidatorsAnalyzer.cs

@@ -13,7 +13,7 @@ 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}`.")
+            $"Each validator specified for this parameter must derive from a compatible `{SymbolNames.CliFxBindingValidatorClass}`.")
     {
     }
 
@@ -28,14 +28,18 @@ public class ParameterMustHaveValidValidatorsAnalyzer : AnalyzerBase
 
         foreach (var validatorType in parameter.ValidatorTypes)
         {
-            // We check against an internal interface because checking against a generic class is a pain
+            var validatorValueType = validatorType
-            var validatorImplementsInterface = validatorType
+                .GetBaseTypes()
-                .AllInterfaces
+                .FirstOrDefault(t => t.ConstructedFrom.DisplayNameMatches(SymbolNames.CliFxBindingValidatorClass))?
-                .Any(s => s.DisplayNameMatches(SymbolNames.CliFxBindingValidatorInterface));
+                .TypeArguments
+                .FirstOrDefault();
 
-            if (!validatorImplementsInterface)
+            // Value passed to the validator must be assignable from the property type
+            if (validatorValueType is null || !validatorValueType.IsAssignableFrom(property.Type))
             {
-                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+                context.ReportDiagnostic(
+                    CreateDiagnostic(propertyDeclaration.Identifier.GetLocation())
+                );
 
                 // No need to report multiple identical diagnostics on the same node
                 break;

CliFx.Analyzers/SystemConsoleShouldBeAvoidedAnalyzer.cs

@@ -65,7 +65,9 @@ public class SystemConsoleShouldBeAvoidedAnalyzer : AnalyzerBase
 
         if (isConsoleInterfaceAvailable)
         {
-            context.ReportDiagnostic(CreateDiagnostic(systemConsoleMemberAccess.GetLocation()));
+            context.ReportDiagnostic(
+                CreateDiagnostic(systemConsoleMemberAccess.GetLocation())
+            );
         }
     }
 

CliFx.Analyzers/Utils/Extensions/RoslynExtensions.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -16,6 +18,22 @@ internal static class RoslynExtensions
             StringComparison.Ordinal
         );
 
+    public static IEnumerable<INamedTypeSymbol> GetBaseTypes(this ITypeSymbol type)
+    {
+        var current = type.BaseType;
+
+        while (current is not null)
+        {
+            yield return current;
+            current = current.BaseType;
+        }
+    }
+
+    public static bool IsAssignableFrom(this ITypeSymbol target, ITypeSymbol source) =>
+        SymbolEqualityComparer.Default.Equals(target, source) ||
+        source.GetBaseTypes().Contains(target, SymbolEqualityComparer.Default) ||
+        source.AllInterfaces.Contains(target, SymbolEqualityComparer.Default);
+
     public static void HandleClassDeclaration(
         this AnalysisContext analysisContext,
         Action<SyntaxNodeAnalysisContext, ClassDeclarationSyntax, ITypeSymbol> analyze)

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -8,9 +8,9 @@
   <ItemGroup>
     <PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
     <PackageReference Include="clipr" Version="1.6.1" />
-    <PackageReference Include="Cocona" Version="1.6.0" />
+    <PackageReference Include="Cocona" Version="2.0.3" />
     <PackageReference Include="CommandLineParser" Version="2.8.0" />
-    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="3.1.0" />
+    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="4.0.1" />
     <PackageReference Include="PowerArgs" Version="3.6.0" />
     <PackageReference Include="System.CommandLine" Version="2.0.0-beta1.20574.7" />
   </ItemGroup>

CliFx.Tests/CliFx.Tests.csproj

@@ -2,10 +2,6 @@
 
   <PropertyGroup>
     <TargetFramework>net6.0</TargetFramework>
-    <IsPackable>false</IsPackable>
-    <IsTestProject>true</IsTestProject>
-    <CollectCoverage>true</CollectCoverage>
-    <CoverletOutputFormat>opencover</CoverletOutputFormat>
   </PropertyGroup>
 
   <ItemGroup>
@@ -14,14 +10,14 @@
 
   <ItemGroup>
     <PackageReference Include="Basic.Reference.Assemblies" Version="1.2.4" />
-    <PackageReference Include="CliWrap" Version="3.3.3" />
+    <PackageReference Include="CliWrap" Version="3.4.1" />
-    <PackageReference Include="FluentAssertions" Version="6.2.0" />
+    <PackageReference Include="FluentAssertions" Version="6.5.1" />
-    <PackageReference Include="GitHubActionsTestLogger" Version="1.2.0" />
+    <PackageReference Include="GitHubActionsTestLogger" Version="1.3.0" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.0.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.1.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" PrivateAssets="all" />
-    <PackageReference Include="coverlet.msbuild" Version="3.1.0" PrivateAssets="all" />
+    <PackageReference Include="coverlet.collector" Version="3.1.2" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Tests/ConsoleSpecs.cs

@@ -5,6 +5,7 @@ using System.Text;
 using System.Threading.Tasks;
 using CliFx.Infrastructure;
 using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
 using CliWrap;
 using CliWrap.Buffered;
 using FluentAssertions;
@@ -139,6 +140,53 @@ public class Command : ICommand
         stdErr.Trim().Should().Be("Hello world");
     }
 
+    [Fact]
+    public async Task Fake_console_can_read_key_presses()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // language=cs
+            @"
+[Command]
+public class Command : ICommand
+{   
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        console.Output.WriteLine(console.ReadKey().Key);
+        console.Output.WriteLine(console.ReadKey().Key);
+        console.Output.WriteLine(console.ReadKey().Key);
+
+        return default;
+    }
+}
+");
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        FakeConsole.EnqueueKey(new ConsoleKeyInfo('0', ConsoleKey.D0, false, false, false));
+        FakeConsole.EnqueueKey(new ConsoleKeyInfo('a', ConsoleKey.A, false, false, false));
+        FakeConsole.EnqueueKey(new ConsoleKeyInfo('\0', ConsoleKey.Backspace, false, false, false));
+
+        var exitCode = await application.RunAsync(
+            Array.Empty<string>(),
+            new Dictionary<string, string>()
+        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        // Assert
+        exitCode.Should().Be(0);
+        stdOut.Trim().Should().ConsistOfLines(
+            "D0",
+            "A",
+            "Backspace"
+        );
+    }
+
     [Fact]
     public void Console_does_not_emit_preamble_when_used_with_encoding_that_has_it()
     {

CliFx.Tests/OptionBindingSpecs.cs

@@ -496,6 +496,83 @@ public class Command : ICommand
         );
     }
 
+    [Fact]
+    public async Task Option_binding_supports_multiple_inheritance_through_default_interface_members()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // language=cs
+            @"
+public static class SharedContext
+{
+    public static int Foo { get; set; }
+
+    public static bool Bar { get; set; }
+}
+
+public interface IHasFoo : ICommand
+{
+    [CommandOption(""foo"")]
+    public int Foo
+    {
+        get => SharedContext.Foo;
+        set => SharedContext.Foo = value;
+    }
+}
+
+public interface IHasBar : ICommand
+{
+    [CommandOption(""bar"")]
+    public bool Bar
+    {
+        get => SharedContext.Bar;
+        set => SharedContext.Bar = value;
+    }
+}
+
+public interface IHasBaz : ICommand
+{
+    public string Baz { get; set; }
+}
+
+[Command]
+public class Command : IHasFoo, IHasBar, IHasBaz
+{
+    [CommandOption(""baz"")]
+    public string Baz { get; set; }
+
+	public ValueTask ExecuteAsync(IConsole console)
+	{
+        console.Output.WriteLine(""Foo = "" + SharedContext.Foo);
+        console.Output.WriteLine(""Bar = "" + SharedContext.Bar);
+        console.Output.WriteLine(""Baz = "" + Baz);
+
+        return default;
+    }
+}
+");
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            new[] { "--foo", "42", "--bar", "--baz", "xyz" }
+        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        // Assert
+        exitCode.Should().Be(0);
+        stdOut.Should().ConsistOfLines(
+            "Foo = 42",
+            "Bar = True",
+            "Baz = xyz"
+        );
+    }
+
     [Fact]
     public async Task Option_binding_does_not_consider_a_negative_number_as_an_option_name_or_short_name()
     {

CliFx.Tests/ParameterBindingSpecs.cs

@@ -120,7 +120,53 @@ public class Command : ICommand
     }
 
     [Fact]
-    public async Task Parameter_binding_fails_if_one_of_the_parameters_has_not_been_provided()
+    public async Task Parameter_is_not_bound_if_there_are_no_arguments_matching_its_order()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // language=cs
+            @"
+[Command]
+public class Command : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+
+    [CommandParameter(1, IsRequired = false)]
+    public string Bar { get; set; } = ""xyz"";
+
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        console.Output.WriteLine(""Foo = "" + Foo);
+        console.Output.WriteLine(""Bar = "" + Bar);
+
+        return default;
+    }
+}");
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            new[] {"abc"},
+            new Dictionary<string, string>()
+        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        // Assert
+        exitCode.Should().Be(0);
+        stdOut.Should().ConsistOfLines(
+            "Foo = abc",
+            "Bar = xyz"
+        );
+    }
+
+    [Fact]
+    public async Task Parameter_binding_fails_if_a_required_parameter_has_not_been_provided()
     {
         // Arrange
         var commandType = DynamicCommandBuilder.Compile(
@@ -153,7 +199,7 @@ public class Command : ICommand
 
         // Assert
         exitCode.Should().NotBe(0);
-        stdErr.Should().Contain("Missing parameter(s)");
+        stdErr.Should().Contain("Missing required parameter(s)");
     }
 
     [Fact]
@@ -190,7 +236,7 @@ public class Command : ICommand
 
         // Assert
         exitCode.Should().NotBe(0);
-        stdErr.Should().Contain("Missing parameter(s)");
+        stdErr.Should().Contain("Missing required parameter(s)");
     }
 
     [Fact]

CliFx/Attributes/CommandOptionAttribute.cs

@@ -29,7 +29,7 @@ public sealed class CommandOptionAttribute : Attribute
     public char? ShortName { get; }
 
     /// <summary>
-    /// Whether this option is required.
+    /// Whether this option is required (default: <c>false</c>).
     /// If an option is required, the user will get an error if they don't set it.
     /// </summary>
     public bool IsRequired { get; set; }

CliFx/Attributes/CommandParameterAttribute.cs

@@ -11,18 +11,26 @@ public sealed class CommandParameterAttribute : Attribute
 {
     /// <summary>
     /// Parameter order.
-    /// </summary>
-    /// <remarks>
     /// Higher order means the parameter appears later, lower order means
     /// it appears earlier.
-    ///
+    /// </summary>
+    /// <remarks>
     /// All parameters in a command must have unique order.
-    ///
     /// Parameter whose type is a non-scalar (e.g. array), must always be the last in order.
     /// Only one non-scalar parameter is allowed in a command.
     /// </remarks>
     public int Order { get; }
 
+    /// <summary>
+    /// Whether this parameter is required (default: <c>true</c>).
+    /// If a parameter is required, the user will get an error if they don't set it.
+    /// </summary>
+    /// <remarks>
+    /// Parameter marked as non-required must always be the last in order.
+    /// Only one non-required parameter is allowed in a command.
+    /// </remarks>
+    public bool IsRequired { get; set; } = true;
+
     /// <summary>
     /// Parameter name.
     /// This is shown to the user in the help text.

CliFx/CliApplication.cs

@@ -112,7 +112,7 @@ public class CliApplication
         // Activate command instance
         var commandInstance = commandSchema == FallbackDefaultCommand.Schema
             ? new FallbackDefaultCommand() // bypass activator
-            : (ICommand) _typeActivator.CreateInstance(commandSchema.Type);
+            : (ICommand)_typeActivator.CreateInstance(commandSchema.Type);
 
         // Assemble help context
         var helpContext = new HelpContext(
@@ -176,7 +176,7 @@ public class CliApplication
     {
         try
         {
-            // Console colors may have already been overriden by the parent process,
+            // Console colors may have already been overridden by the parent process,
             // so we need to reset it to make sure that everything we write looks properly.
             _console.ResetColor();
 

CliFx/CliFx.csproj

@@ -4,6 +4,7 @@
     <TargetFrameworks>netstandard2.1;netstandard2.0</TargetFrameworks>
     <Authors>$(Company)</Authors>
     <Description>Declarative framework for building command line applications</Description>
+    <IsPackable>true</IsPackable>
     <PackageTags>command line executable interface framework parser arguments cli app application net core</PackageTags>
     <PackageProjectUrl>https://github.com/Tyrrrz/CliFx</PackageProjectUrl>
     <PackageReleaseNotes>https://github.com/Tyrrrz/CliFx/blob/master/Changelog.md</PackageReleaseNotes>
@@ -34,6 +35,16 @@
   <ItemGroup>
     <ProjectReference Include="../CliFx.Analyzers/CliFx.Analyzers.csproj" ReferenceOutputAssembly="false" OutputItemType="Analyzer" />
     <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/CliFx.Analyzers.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/Microsoft.CodeAnalysis.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/Microsoft.CodeAnalysis.CSharp.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Buffers.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Collections.Immutable.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Memory.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Numerics.Vectors.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Reflection.Metadata.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Runtime.CompilerServices.Unsafe.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Text.Encoding.CodePages.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+    <None Include="../CliFx.Analyzers/bin/$(Configuration)/netstandard2.0/System.Threading.Tasks.Extensions.dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
   </ItemGroup>
 
 </Project>

CliFx/CommandBinder.cs

@@ -27,7 +27,7 @@ internal class CommandBinder
         // Custom converter
         if (memberSchema.ConverterType is not null)
         {
-            var converter = (IBindingConverter) _typeActivator.CreateInstance(memberSchema.ConverterType);
+            var converter = (IBindingConverter)_typeActivator.CreateInstance(memberSchema.ConverterType);
             return converter.Convert(rawValue);
         }
 
@@ -43,12 +43,6 @@ internal class CommandBinder
             return string.IsNullOrWhiteSpace(rawValue) || bool.Parse(rawValue);
         }
 
-        // IConvertible primitives (int, double, char, etc)
-        if (targetType.IsConvertible())
-        {
-            return Convert.ChangeType(rawValue, targetType, _formatProvider);
-        }
-
         // Special case for DateTimeOffset
         if (targetType == typeof(DateTimeOffset))
         {
@@ -68,6 +62,12 @@ internal class CommandBinder
             return Enum.Parse(targetType, rawValue!, true);
         }
 
+        // Convertible primitives (int, double, char, etc)
+        if (targetType.Implements(typeof(IConvertible)))
+        {
+            return Convert.ChangeType(rawValue, targetType, _formatProvider);
+        }
+
         // Nullable<T>
         var nullableUnderlyingType = targetType.TryGetNullableUnderlyingType();
         if (nullableUnderlyingType is not null)
@@ -78,24 +78,24 @@ internal class CommandBinder
         }
 
         // String-constructible (FileInfo, etc)
-        var stringConstructor = targetType.GetConstructor(new[] {typeof(string)});
+        var stringConstructor = targetType.GetConstructor(new[] { typeof(string) });
         if (stringConstructor is not null)
         {
-            return stringConstructor.Invoke(new object?[] {rawValue});
+            return stringConstructor.Invoke(new object?[] { rawValue });
         }
 
         // String-parseable (with IFormatProvider)
         var parseMethodWithFormatProvider = targetType.TryGetStaticParseMethod(true);
         if (parseMethodWithFormatProvider is not null)
         {
-            return parseMethodWithFormatProvider.Invoke(null, new object?[] {rawValue, _formatProvider});
+            return parseMethodWithFormatProvider.Invoke(null, new object?[] { rawValue, _formatProvider });
         }
 
         // String-parseable (without IFormatProvider)
         var parseMethod = targetType.TryGetStaticParseMethod();
         if (parseMethod is not null)
         {
-            return parseMethod.Invoke(null, new object?[] {rawValue});
+            return parseMethod.Invoke(null, new object?[] { rawValue });
         }
 
         throw CliFxException.InternalError(
@@ -126,10 +126,10 @@ internal class CommandBinder
         }
 
         // Array-constructible (List<T>, HashSet<T>, etc)
-        var arrayConstructor = targetEnumerableType.GetConstructor(new[] {arrayType});
+        var arrayConstructor = targetEnumerableType.GetConstructor(new[] { arrayType });
         if (arrayConstructor is not null)
         {
-            return arrayConstructor.Invoke(new object?[] {array});
+            return arrayConstructor.Invoke(new object?[] { array });
         }
 
         throw CliFxException.InternalError(
@@ -192,7 +192,7 @@ internal class CommandBinder
 
         foreach (var validatorType in memberSchema.ValidatorTypes)
         {
-            var validator = (IBindingValidator) _typeActivator.CreateInstance(validatorType);
+            var validator = (IBindingValidator)_typeActivator.CreateInstance(validatorType);
             var error = validator.Validate(convertedValue);
 
             if (error is not null)
@@ -223,7 +223,7 @@ internal class CommandBinder
     {
         // Ensure there are no unexpected parameters and that all parameters are provided
         var remainingParameterInputs = commandInput.Parameters.ToList();
-        var remainingParameterSchemas = commandSchema.Parameters.ToList();
+        var remainingRequiredParameterSchemas = commandSchema.Parameters.Where(p => p.IsRequired).ToList();
 
         var position = 0;
 
@@ -238,7 +238,7 @@ internal class CommandBinder
             {
                 var parameterInput = commandInput.Parameters[position];
 
-                var rawValues = new[] {parameterInput.Value};
+                var rawValues = new[] { parameterInput.Value };
                 BindMember(parameterSchema, commandInstance, rawValues);
 
                 position++;
@@ -258,7 +258,7 @@ internal class CommandBinder
                 remainingParameterInputs.RemoveRange(parameterInputs);
             }
 
-            remainingParameterSchemas.Remove(parameterSchema);
+            remainingRequiredParameterSchemas.Remove(parameterSchema);
         }
 
         if (remainingParameterInputs.Any())
@@ -272,13 +272,13 @@ internal class CommandBinder
             );
         }
 
-        if (remainingParameterSchemas.Any())
+        if (remainingRequiredParameterSchemas.Any())
         {
             throw CliFxException.UserError(
-                "Missing parameter(s):" +
+                "Missing required parameter(s):" +
                 Environment.NewLine +
-                remainingParameterSchemas
+                remainingRequiredParameterSchemas
-                    .Select(o => o.GetFormattedIdentifier())
+                    .Select(p => p.GetFormattedIdentifier())
                     .JoinToString(" ")
             );
         }
@@ -316,7 +316,7 @@ internal class CommandBinder
             else if (environmentVariableInput is not null)
             {
                 var rawValues = optionSchema.Property.IsScalar()
-                    ? new[] {environmentVariableInput.Value}
+                    ? new[] { environmentVariableInput.Value }
                     : environmentVariableInput.SplitValues();
 
                 BindMember(optionSchema, commandInstance, rawValues);

CliFx/Extensibility/BindingValidator.cs

@@ -23,7 +23,7 @@ public abstract class BindingValidator<T> : IBindingValidator
 
     /// <summary>
     /// Validates the value bound to a parameter or an option.
-    /// Returns <code>null</code> if validation is successful, or an error in case of failure.
+    /// Returns null if validation is successful, or an error in case of failure.
     /// </summary>
     /// <remarks>
     /// You can use the utility methods <see cref="Ok"/> and <see cref="Error"/> to
@@ -31,5 +31,5 @@ public abstract class BindingValidator<T> : IBindingValidator
     /// </remarks>
     public abstract BindingValidationError? Validate(T? value);
 
-    BindingValidationError? IBindingValidator.Validate(object? value) => Validate((T?) value);
+    BindingValidationError? IBindingValidator.Validate(object? value) => Validate((T?)value);
 }

CliFx/Formatting/HelpConsoleFormatter.cs

@@ -156,8 +156,16 @@ internal class HelpConsoleFormatter : ConsoleFormatter
         WriteHeader("Parameters");
 
         foreach (var parameterSchema in _context.CommandSchema.Parameters.OrderBy(p => p.Order))
+        {
+            if (parameterSchema.IsRequired)
             {
                 Write(ConsoleColor.Red, "* ");
+            }
+            else
+            {
+                WriteHorizontalMargin();
+            }
+
             Write(ConsoleColor.DarkCyan, $"{parameterSchema.Name}");
 
             WriteColumnMargin();
@@ -199,6 +207,12 @@ internal class HelpConsoleFormatter : ConsoleFormatter
                 Write(' ');
             }
             
+            // Default value
+            if (!parameterSchema.IsRequired)
+            {
+                WriteDefaultValue(parameterSchema);
+            }
+
             WriteLine();
         }
     }
@@ -290,7 +304,16 @@ internal class HelpConsoleFormatter : ConsoleFormatter
             // Default value
             if (!optionSchema.IsRequired)
             {
-                var defaultValue = _context.CommandDefaultValues.GetValueOrDefault(optionSchema);
+                WriteDefaultValue(optionSchema);
+            }
+
+            WriteLine();
+        }
+    }
+
+    private void WriteDefaultValue(IMemberSchema schema)
+    {
+        var defaultValue = _context.CommandDefaultValues.GetValueOrDefault(schema);
         if (defaultValue is not null)
         {
             // Non-Scalar
@@ -340,10 +363,6 @@ internal class HelpConsoleFormatter : ConsoleFormatter
         }
     }
 
-            WriteLine();
-        }
-    }
-
     private void WriteCommandChildren()
     {
         var childCommandSchemas = _context

CliFx/Infrastructure/ConsoleReader.cs

@@ -1,11 +1,16 @@
-using System.IO;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.Runtime.CompilerServices;
 using System.Text;
+using System.Threading.Tasks;
 
 namespace CliFx.Infrastructure;
 
 /// <summary>
 /// Implements a <see cref="TextReader"/> for reading characters from a console stream.
 /// </summary>
+// Both the underlying stream AND the stream reader must be synchronized!
+// https://github.com/Tyrrrz/CliFx/issues/123
 public partial class ConsoleReader : StreamReader
 {
     /// <summary>
@@ -29,6 +34,67 @@ public partial class ConsoleReader : StreamReader
         : this(console, stream, System.Console.InputEncoding)
     {
     }
+
+    // The following overrides are required to establish thread-safe behavior
+    // in methods deriving from StreamReader.
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override int Peek() => base.Peek();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override int Read() => base.Read();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override int Read(char[] buffer, int index, int count) =>
+        base.Read(buffer, index, count);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override int ReadBlock(char[] buffer, int index, int count) =>
+        base.ReadBlock(buffer, index, count);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override string? ReadLine() => base.ReadLine();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override string ReadToEnd() => base.ReadToEnd();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task<int> ReadAsync(char[] buffer, int index, int count) =>
+        // Must be non-async to work with locks
+        Task.FromResult(Read(buffer, index, count));
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task<int> ReadBlockAsync(char[] buffer, int index, int count) =>
+        // Must be non-async to work with locks
+        Task.FromResult(ReadBlock(buffer, index, count));
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task<string?> ReadLineAsync() =>
+        // Must be non-async to work with locks
+        Task.FromResult(ReadLine());
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task<string> ReadToEndAsync() =>
+        // Must be non-async to work with locks
+        Task.FromResult(ReadToEnd());
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Close() => base.Close();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    protected override void Dispose(bool disposing) => base.Dispose(disposing);
 }
 
 public partial class ConsoleReader

CliFx/Infrastructure/ConsoleWriter.cs

@@ -1,5 +1,8 @@
-using System.IO;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.Runtime.CompilerServices;
 using System.Text;
+using System.Threading.Tasks;
 using CliFx.Utils;
 
 namespace CliFx.Infrastructure;
@@ -7,6 +10,8 @@ namespace CliFx.Infrastructure;
 /// <summary>
 /// Implements a <see cref="TextWriter"/> for writing characters to a console stream.
 /// </summary>
+// Both the underlying stream AND the stream writer must be synchronized!
+// https://github.com/Tyrrrz/CliFx/issues/123
 public partial class ConsoleWriter : StreamWriter
 {
     /// <summary>
@@ -30,6 +35,239 @@ public partial class ConsoleWriter : StreamWriter
         : this(console, stream, System.Console.OutputEncoding)
     {
     }
+
+    // The following overrides are required to establish thread-safe behavior
+    // in methods deriving from StreamWriter.
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(char[] buffer, int index, int count) => base.Write(buffer, index, count);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(char[] buffer) => base.Write(buffer);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(char value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(string? value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(string format, object? arg0) => base.Write(format, arg0);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(string format, object? arg0, object? arg1) =>
+        base.Write(format, arg0, arg1);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(string format, object? arg0, object? arg1, object? arg2) =>
+        base.Write(format, arg0, arg1, arg2);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(string format, params object?[] arg) => base.Write(format, arg);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(bool value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(int value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(long value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(uint value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(ulong value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(float value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(double value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(decimal value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Write(object? value) => base.Write(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteAsync(char[] buffer, int index, int count)
+    {
+        // Must be non-async to work with locks
+        Write(buffer, index, count);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteAsync(char value)
+    {
+        // Must be non-async to work with locks
+        Write(value);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteAsync(string? value)
+    {
+        // Must be non-async to work with locks
+        Write(value);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine() => base.WriteLine();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(char[] buffer, int index, int count) =>
+        base.WriteLine(buffer, index, count);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(char[] buffer) => base.WriteLine(buffer);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(char value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(string? value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(string format, object? arg0) => base.WriteLine(format, arg0);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(string format, object? arg0, object? arg1) =>
+        base.WriteLine(format, arg0, arg1);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(string format, object? arg0, object? arg1, object? arg2) =>
+        base.WriteLine(format, arg0, arg1, arg2);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(string format, params object?[] arg) =>
+        base.WriteLine(format, arg);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(bool value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(int value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(long value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(uint value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(ulong value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(float value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(double value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(decimal value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void WriteLine(object? value) => base.WriteLine(value);
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteLineAsync()
+    {
+        // Must be non-async to work with locks
+        WriteLine();
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteLineAsync(char value)
+    {
+        // Must be non-async to work with locks
+        WriteLine(value);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteLineAsync(char[] buffer, int index, int count)
+    {
+        // Must be non-async to work with locks
+        WriteLine(buffer, index, count);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task WriteLineAsync(string? value)
+    {
+        // Must be non-async to work with locks
+        WriteLine(value);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Flush() => base.Flush();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override Task FlushAsync()
+    {
+        // Must be non-async to work with locks
+        Flush();
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    public override void Close() => base.Close();
+
+    /// <inheritdoc />
+    [ExcludeFromCodeCoverage, MethodImpl(MethodImplOptions.Synchronized)]
+    protected override void Dispose(bool disposing) => base.Dispose(disposing);
 }
 
 public partial class ConsoleWriter

CliFx/Infrastructure/DefaultTypeActivator.cs

@@ -16,14 +16,15 @@ public class DefaultTypeActivator : ITypeActivator
         {
             return Activator.CreateInstance(type);
         }
-        catch (Exception ex)
+        // Only catch MemberAccessException because the constructor can throw for its own reasons too
+        catch (MemberAccessException ex)
         {
             throw CliFxException.InternalError(
-                $"Failed to create an instance of type `{type.FullName}`." +
+                $"Failed to create an instance of type `{type.FullName}`, could not access the constructor." +
                 Environment.NewLine +
                 "Default type activator is only capable of instantiating a type if it has a public parameterless constructor." +
                 Environment.NewLine +
-                "To fix this, either add a parameterless constructor to the type or configure a custom activator on the application.",
+                "To fix this, either add a parameterless constructor to the type or configure a custom activator for the application.",
                 ex
             );
         }

CliFx/Infrastructure/FakeConsole.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.IO;
 using System.Threading;
 
@@ -14,6 +15,7 @@ namespace CliFx.Infrastructure;
 public class FakeConsole : IConsole, IDisposable
 {
     private readonly CancellationTokenSource _cancellationTokenSource = new();
+    private readonly ConcurrentQueue<ConsoleKeyInfo> _keys = new();
 
     /// <inheritdoc />
     public ConsoleReader Input { get; }
@@ -91,9 +93,18 @@ public class FakeConsole : IConsole, IDisposable
     }
 
     /// <inheritdoc />
-    public void ReadKey(bool intercept = false)
+    public ConsoleKeyInfo ReadKey(bool intercept = false) =>
-    {
+        _keys.TryDequeue(out var key)
-    }
+            ? key
+            : throw new InvalidOperationException(
+                "Cannot read key because there are no key presses enqueued. " +
+                $"Use the `{nameof(EnqueueKey)}(...)` method to simulate a key press."
+            );
+
+    /// <summary>
+    /// Enqueues a simulated key press, which can then be read by calling <see cref="ReadKey"/>.
+    /// </summary>
+    public void EnqueueKey(ConsoleKeyInfo key) => _keys.Enqueue(key);
 
     /// <inheritdoc />
     public virtual void Dispose() => _cancellationTokenSource.Dispose();

CliFx/Infrastructure/IConsole.cs

@@ -91,7 +91,7 @@ public interface IConsole
     /// <summary>
     /// Obtains the next character or function key pressed by the user.
     /// </summary>
-    void ReadKey(bool intercept = false);
+    ConsoleKeyInfo ReadKey(bool intercept = false);
 }
 
 /// <summary>

CliFx/Infrastructure/SystemConsole.cs

@@ -94,7 +94,7 @@ public class SystemConsole : IConsole, IDisposable
     public void Clear() => Console.Clear();
 
     /// <inheritdoc />
-    public void ReadKey(bool intercept = false) => Console.ReadKey(intercept);
+    public ConsoleKeyInfo ReadKey(bool intercept = false) => Console.ReadKey(intercept);
 
     /// <inheritdoc />
     public void Dispose()

CliFx/Schema/CommandSchema.cs

@@ -87,12 +87,27 @@ internal partial class CommandSchema
             ? new[] {OptionSchema.HelpOption, OptionSchema.VersionOption}
             : new[] {OptionSchema.HelpOption};
 
-        var parameterSchemas = type.GetProperties()
+        var properties = type
+            // Get properties directly on command type
+            .GetProperties()
+            // Get non-abstract properties on interfaces (to support default interfaces members)
+            .Union(type
+                .GetInterfaces()
+                // Only interfaces implementing ICommand for explicitness
+                .Where(i => typeof(ICommand).IsAssignableFrom(i) && i != typeof(ICommand))
+                .SelectMany(i => i
+                    .GetProperties()
+                    .Where(p => !p.GetMethod.IsAbstract && !p.SetMethod.IsAbstract)
+                )
+            )
+            .ToArray();
+
+        var parameterSchemas = properties
             .Select(ParameterSchema.TryResolve)
             .WhereNotNull()
             .ToArray();
 
-        var optionSchemas = type.GetProperties()
+        var optionSchemas = properties
             .Select(OptionSchema.TryResolve)
             .WhereNotNull()
             .Concat(implicitOptionSchemas)

CliFx/Schema/ParameterSchema.cs

@@ -13,6 +13,8 @@ internal partial class ParameterSchema : IMemberSchema
 
     public string Name { get; }
 
+    public bool IsRequired { get; }
+
     public string? Description { get; }
 
     public Type? ConverterType { get; }
@@ -23,6 +25,7 @@ internal partial class ParameterSchema : IMemberSchema
         IPropertyDescriptor property,
         int order,
         string name,
+        bool isRequired,
         string? description,
         Type? converterType,
         IReadOnlyList<Type> validatorTypes)
@@ -30,6 +33,7 @@ internal partial class ParameterSchema : IMemberSchema
         Property = property;
         Order = order;
         Name = name;
+        IsRequired = isRequired;
         Description = description;
         ConverterType = converterType;
         ValidatorTypes = validatorTypes;
@@ -55,6 +59,7 @@ internal partial class ParameterSchema
             new BindablePropertyDescriptor(property),
             attribute.Order,
             name,
+            attribute.IsRequired,
             description,
             attribute.Converter,
             attribute.Validators

CliFx/Utils/Extensions/TypeExtensions.cs

@@ -59,27 +59,4 @@ internal static class TypeExtensions
         var toStringMethod = type.GetMethod(nameof(ToString), Type.EmptyTypes);
         return toStringMethod?.GetBaseDefinition()?.DeclaringType != toStringMethod?.DeclaringType;
     }
-
-    // Types supported by `Convert.ChangeType(...)`
-    private static readonly HashSet<Type> ConvertibleTypes = new()
-    {
-        typeof(bool),
-        typeof(char),
-        typeof(sbyte),
-        typeof(byte),
-        typeof(short),
-        typeof(ushort),
-        typeof(int),
-        typeof(uint),
-        typeof(long),
-        typeof(ulong),
-        typeof(float),
-        typeof(double),
-        typeof(decimal),
-        typeof(DateTime),
-        typeof(string),
-        typeof(object)
-    };
-
-    public static bool IsConvertible(this Type type) => ConvertibleTypes.Contains(type);
 }

CliFx/Utils/NoPreambleEncoding.cs

@@ -8,6 +8,8 @@ namespace CliFx.Utils;
 // https://github.com/dotnet/runtime/blob/01b7e73cd378145264a7cb7a09365b41ed42b240/src/libraries/Common/src/System/Text/ConsoleEncoding.cs
 // Also see:
 // https://source.dot.net/#System.Console/ConsoleEncoding.cs,5eedd083a4a4f4a2
+// Majority of overrides are just proxy calls to avoid potentially more expensive base behavior.
+// The important part is the GetPreamble() method that has been overriden to return an empty array.
 internal class NoPreambleEncoding : Encoding
 {
     private readonly Encoding _underlyingEncoding;
@@ -72,20 +74,20 @@ internal class NoPreambleEncoding : Encoding
     public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex) =>
         _underlyingEncoding.GetBytes(chars, charIndex, charCount, bytes, byteIndex);
 
-    [ExcludeFromCodeCoverage]
-    public override byte[] GetBytes(char[] chars) => _underlyingEncoding.GetBytes(chars);
-
     [ExcludeFromCodeCoverage]
     public override byte[] GetBytes(char[] chars, int index, int count) =>
         _underlyingEncoding.GetBytes(chars, index, count);
 
     [ExcludeFromCodeCoverage]
-    public override byte[] GetBytes(string s) => _underlyingEncoding.GetBytes(s);
+    public override byte[] GetBytes(char[] chars) => _underlyingEncoding.GetBytes(chars);
 
     [ExcludeFromCodeCoverage]
     public override int GetBytes(string s, int charIndex, int charCount, byte[] bytes, int byteIndex) =>
         _underlyingEncoding.GetBytes(s, charIndex, charCount, bytes, byteIndex);
 
+    [ExcludeFromCodeCoverage]
+    public override byte[] GetBytes(string s) => _underlyingEncoding.GetBytes(s);
+
     [ExcludeFromCodeCoverage]
     public override int GetCharCount(byte[] bytes, int index, int count) =>
         _underlyingEncoding.GetCharCount(bytes, index, count);

CliFx/Utils/Polyfills.Collections.cs

@@ -0,0 +1,26 @@
+// ReSharper disable CheckNamespace
+
+#if NETSTANDARD2_0
+using System.Collections.Generic;
+
+internal static class CollectionPolyfills
+{
+    public static void Deconstruct<TKey, TValue>(this KeyValuePair<TKey, TValue> pair, out TKey key, out TValue value)
+    {
+        key = pair.Key;
+        value = pair.Value;
+    }
+
+    public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dic, TKey key) =>
+        dic.TryGetValue(key!, out var result) ? result! : default!;
+}
+
+namespace System.Linq
+{
+    internal static class LinqPolyfills
+    {
+        public static HashSet<T> ToHashSet<T>(this IEnumerable<T> source, IEqualityComparer<T> comparer) =>
+            new(source, comparer);
+    }
+}
+#endif

CliFx/Utils/Polyfills.Streams.cs

@@ -0,0 +1,11 @@
+// ReSharper disable CheckNamespace
+
+#if NETSTANDARD2_0
+using System.IO;
+
+internal static class StreamPolyfills
+{
+    public static void Write(this Stream stream, byte[] buffer) =>
+        stream.Write(buffer, 0, buffer.Length);
+}
+#endif

CliFx/Utils/Polyfills.Strings.cs

@@ -0,0 +1,12 @@
+// ReSharper disable CheckNamespace
+
+#if NETSTANDARD2_0
+internal static class StringPolyfills
+{
+    public static bool StartsWith(this string str, char c) =>
+        str.Length > 0 && str[0] == c;
+
+    public static bool EndsWith(this string str, char c) =>
+        str.Length > 0 && str[str.Length - 1] == c;
+}
+#endif

CliFx/Utils/Polyfills.cs

@@ -1,53 +0,0 @@
-// ReSharper disable CheckNamespace
-
-#if NETSTANDARD2_0
-using System;
-using System.Collections.Generic;
-using System.IO;
-
-internal static partial class PolyfillExtensions
-{
-    public static bool StartsWith(this string str, char c) =>
-        str.Length > 0 && str[0] == c;
-
-    public static bool EndsWith(this string str, char c) =>
-        str.Length > 0 && str[str.Length - 1] == c;
-
-    public static string[] Split(this string str, char separator, StringSplitOptions splitOptions) =>
-        str.Split(new[] {separator}, splitOptions);
-}
-
-internal static partial class PolyfillExtensions
-{
-    public static void Deconstruct<TKey, TValue>(this KeyValuePair<TKey, TValue> pair, out TKey key, out TValue value)
-    {
-        key = pair.Key;
-        value = pair.Value;
-    }
-}
-
-internal static partial class PolyfillExtensions
-{
-    public static void Write(this Stream stream, byte[] buffer) =>
-        stream.Write(buffer, 0, buffer.Length);
-}
-
-
-namespace System.Linq
-{
-    internal static class PolyfillExtensions
-    {
-        public static HashSet<T> ToHashSet<T>(this IEnumerable<T> source, IEqualityComparer<T> comparer) =>
-            new(source, comparer);
-    }
-}
-
-namespace System.Collections.Generic
-{
-    internal static class PolyfillExtensions
-    {
-        public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dic, TKey key) =>
-            dic.TryGetValue(key!, out var result) ? result! : default!;
-    }
-}
-#endif

Directory.Build.props

@@ -1,12 +1,13 @@
 <Project>
 
   <PropertyGroup>
-    <Version>2.1</Version>
+    <Version>2.2.3</Version>
     <Company>Tyrrrz</Company>
-    <Copyright>Copyright (C) Alexey Golub</Copyright>
+    <Copyright>Copyright (C) Oleksii Holub</Copyright>
     <LangVersion>latest</LangVersion>
     <Nullable>enable</Nullable>
     <WarningsAsErrors>nullable</WarningsAsErrors>
+    <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <!-- Disable nullability warnings on older frameworks because there is no nullability info for BCL -->

License.txt

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2019-2022 Alexey Golub
+Copyright (c) 2019-2022 Oleksii Holub
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

Readme.md

@@ -1,22 +1,33 @@
 # CliFx
 
-[![Build](https://github.com/Tyrrrz/CliFx/workflows/main/badge.svg?branch=master)](https://github.com/Tyrrrz/CliFx/actions)
+[![Made in Ukraine](https://img.shields.io/badge/made_in-ukraine-ffd700.svg?labelColor=0057b7)](https://vshymanskyy.github.io/StandWithUkraine)
-[![Coverage](https://codecov.io/gh/Tyrrrz/CliFx/branch/master/graph/badge.svg)](https://codecov.io/gh/Tyrrrz/CliFx)
+[![Build](https://img.shields.io/github/workflow/status/Tyrrrz/CliFx/CI/master)](https://github.com/Tyrrrz/CliFx/actions)
+[![Coverage](https://img.shields.io/codecov/c/github/Tyrrrz/CliFx/master)](https://codecov.io/gh/Tyrrrz/CliFx)
 [![Version](https://img.shields.io/nuget/v/CliFx.svg)](https://nuget.org/packages/CliFx)
 [![Downloads](https://img.shields.io/nuget/dt/CliFx.svg)](https://nuget.org/packages/CliFx)
 [![Discord](https://img.shields.io/discord/869237470565392384?label=discord)](https://discord.gg/2SUWKFnHSm)
-[![Donate](https://img.shields.io/badge/donate-$$$-purple.svg)](https://tyrrrz.me/donate)
+[![Donate](https://img.shields.io/badge/donate-$$$-8a2be2.svg)](https://tyrrrz.me/donate)
+[![Fuck Russia](https://img.shields.io/badge/fuck-russia-e4181c.svg?labelColor=000000)](https://twitter.com/tyrrrz/status/1495972128977571848)
 
-✅ **Project status: active**. [What does it mean?](https://github.com/Tyrrrz/.github/blob/master/docs/project-status.md)
+> 🟢 **Project status**: active<sup>[[?]](https://github.com/Tyrrrz/.github/blob/master/docs/project-status.md)</sup>
 
 **CliFx** is a simple to use, yet powerful framework for building command line applications.
 Its primary goal is to completely take over the user input layer, allowing you to forget about infrastructural concerns and instead focus on writing your application.
 
-💬 **If you want to chat, join my [Discord server](https://discord.gg/2SUWKFnHSm)**.
+## Terms of use
 
-## Download
+By using this project or its source code, for any purpose and in any shape or form, you grant your **implicit agreement** to all the following statements:
 
-📦 [NuGet](https://nuget.org/packages/CliFx): `dotnet add package CliFx`
+- You **condemn Russia and its military aggression against Ukraine**
+- You **recognize that Russia is an occupant that unlawfully invaded a sovereign state**
+- You **support Ukraine's territorial integrity, including its claims over temporarily occupied territories of Crimea and Donbas**
+- You **reject false narratives perpetuated by Russian state propaganda**
+
+To learn more about the war and how you can help, [click here](https://tyrrrz.me). Glory to Ukraine! 🇺🇦
+
+## Install
+
+- 📦 [NuGet](https://nuget.org/packages/CliFx): `dotnet add package CliFx`
 
 ## Features
 
@@ -168,7 +179,7 @@ In case the user forgets to specify the `value` parameter, the application will
 ```sh
 > dotnet myapp.dll -b 10
 
-Missing parameter(s):
+Missing required parameter(s):
 <value>
 ```
 
@@ -193,11 +204,12 @@ OPTIONS
 
 Overall, parameters and options are both used to consume input from the command line, but they differ in a few important ways:
 
-- Parameters are identified by their relative order. Options are identified by their name or a single-character short name.
+|                    | Parameters                                                                                            | Options                                                                                         |
-- Parameters technically also have a name, but it's only used in the help text.
+|--------------------|-------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------|
-- Parameters are always required. Options are normally optional, but can also be configured to require a value.
+| **Identification** | Positional (by relative order).                                                                       | Named (by name or short name).                                                                  |
-- Options can be configured to use an environment variable as a fallback.
+| **Requiredness**   | Required by default. Only the last parameter can be configured to be optional.                        | Optional by default. Any option can be configured to be required without limitations.           |
-- Both parameters and options can take multiple values, but there can only be one such parameter in a command and it must be the last in order. Options are not limited in this regard.
+| **Arity**          | Depends on the property type. Only the last parameter can be bound to a non-scalar type (i.e. array). | Depends on the property type. Any option can be bound to a non-scalar type without limitations. |
+| **Fallback**       | —                                                                                                     | Can be configured to use an environment variable as fallback, in case the option isn't set.     |
 
 As a general guideline, it's recommended to use parameters for required inputs that the command can't function without.
 Use options for all other non-required inputs or when specifying the name explicitly makes the usage clearer.
@@ -226,7 +238,7 @@ Similarly, unseparated arguments in the form of `myapp -ofile` will be treated a
 
 Because of these rules, order of arguments is semantically important and must always follow this pattern:
 
-```ini
+```txt
 [directives] [command name] [parameters] [options]
 ```