Add support for optional parameters (#119)

CliFx.Analyzers.Tests/ParameterMustBeLastIfNotRequiredAnalyzerSpecs.cs

@@ -0,0 +1,76 @@
+using CliFx.Analyzers.Tests.Utils;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Xunit;
+
+namespace CliFx.Analyzers.Tests;
+
+public class ParameterMustBeLastIfNotRequiredAnalyzerSpecs
+{
+    private static DiagnosticAnalyzer Analyzer { get; } = new ParameterMustBeLastIfNotRequiredAnalyzer();
+
+    [Fact]
+    public void Analyzer_reports_an_error_if_a_parameter_is_not_required_and_is_not_last_parameter()
+    {
+        // 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"", 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_isRequired_is_false_on_last_parameter()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"", IsRequired = true)]
+    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_on_a_property_when_isRequired_is_not_set()
+    {
+        // Arrange
+        // language=cs
+        const string code = @"
+[Command]
+public class MyCommand : ICommand
+{
+    [CommandParameter(0, Name = ""foo"")]
+    public string Foo { get; set; }
+    
+    [CommandParameter(1, Name = ""bar"")]
+    public string Bar { get; set; }
+
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}";
+
+        // Act & assert
+        Analyzer.Should().NotProduceDiagnostics(code);
+    }
+}

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;
     }
@@ -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 null;
-
-        return FromAttribute(attribute);
+        return attribute is not null
+            ? FromAttribute(attribute)
+            : null;
     }
 
     public static bool IsParameterProperty(IPropertySymbol property) =>

CliFx.Analyzers/ParameterMustBeLastIfNotRequiredAnalyzer.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Linq;
+using CliFx.Analyzers.ObjectModel;
+using CliFx.Analyzers.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace CliFx.Analyzers;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class ParameterMustBeLastIfNotRequiredAnalyzer : AnalyzerBase
+{
+    public ParameterMustBeLastIfNotRequiredAnalyzer()
+        : base(
+            "Only last parameter can be optional",
+            "IsRequired can only be set to false on the last parameter.")
+    {
+    }
+
+    private void Analyze(
+        SyntaxNodeAnalysisContext context,
+        PropertyDeclarationSyntax propertyDeclaration,
+        IPropertySymbol property)
+    {
+        if (property.ContainingType is null)
+            return;
+
+        var parameter = CommandParameterSymbol.TryResolve(property);
+        
+        if (parameter is null || 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 (parameter.IsRequired is false && parameter.Order < otherParameter.Order)
+            {
+                context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
+            }
+        }
+    }
+
+    public override void Initialize(AnalysisContext context)
+    {
+        base.Initialize(context);
+        context.HandlePropertyDeclaration(Analyze);
+    }
+}

CliFx.Tests/ParameterBindingSpecs.cs

@@ -153,7 +153,7 @@ 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 +190,7 @@ 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/CommandParameterAttribute.cs

@@ -23,6 +23,13 @@ public sealed class CommandParameterAttribute : Attribute
     /// </remarks>
     public int Order { get; }
     
+    /// <summary>
+    /// Whether this parameter is required. (default: true)
+    /// If a parameter is required, the user will get an error if they don't set it.
+    /// Only the last parameter in order can be optional.
+    /// </summary>
+    public bool IsRequired { get; set; } = true;
+
     /// <summary>
     /// Parameter name.
     /// This is shown to the user in the help text.

CliFx/CommandBinder.cs

@@ -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;
 
@@ -258,7 +258,7 @@ internal class CommandBinder
                 remainingParameterInputs.RemoveRange(parameterInputs);
             }
 
-            remainingParameterSchemas.Remove(parameterSchema);
+            remainingRequiredParameterSchemas.Remove(parameterSchema);
         }
 
         if (remainingParameterInputs.Any())
@@ -272,12 +272,12 @@ 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())
                     .JoinToString(" ")
             );

CliFx/Formatting/HelpConsoleFormatter.cs

@@ -157,7 +157,15 @@ internal class HelpConsoleFormatter : ConsoleFormatter
 
         foreach (var parameterSchema in _context.CommandSchema.Parameters.OrderBy(p => p.Order))
         {
-            Write(ConsoleColor.Red, "* ");
+            if (parameterSchema.IsRequired)
+            {
+                Write(ConsoleColor.Red, "* ");
+            }
+            else
+            {
+                WriteHorizontalMargin();
+            }
+
             Write(ConsoleColor.DarkCyan, $"{parameterSchema.Name}");
 
             WriteColumnMargin();

CliFx/Schema/ParameterSchema.cs

@@ -15,15 +15,17 @@ internal partial class ParameterSchema : IMemberSchema
 
     public string? Description { get; }
    
+    public bool IsRequired { get; }
+    
     public Type? ConverterType { get; }
 
     public IReadOnlyList<Type> ValidatorTypes { get; }
 
-    public ParameterSchema(
-        IPropertyDescriptor property,
+    public ParameterSchema(IPropertyDescriptor property,
         int order,
         string name,
         string? description,
+        bool isRequired,
         Type? converterType,
         IReadOnlyList<Type> validatorTypes)
     {
@@ -31,6 +33,7 @@ internal partial class ParameterSchema : IMemberSchema
         Order = order;
         Name = name;
         Description = description;
+        IsRequired = isRequired;
         ConverterType = converterType;
         ValidatorTypes = validatorTypes;
     }
@@ -56,6 +59,7 @@ internal partial class ParameterSchema
             attribute.Order,
             name,
             description,
+            attribute.IsRequired,
             attribute.Converter,
             attribute.Validators
         );