Add source-generated Program entry point when no Main() is defined (#183)

Author: Copilot

…rs/Generator.CommandDescriptorEmitter.cs ….Generators/Binding/CommandDescriptor.csCliFx.Generators/Generator.CommandDescriptorEmitter.cs renamed to CliFx.Generators/Binding/CommandDescriptor.cs CliFx.Generators/Generator.CommandDescriptorEmitter.cs renamed to CliFx.Generators/Binding/CommandDescriptor.cs

@@ -1,14 +1,13 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using CliFx.Generators.Binding;
 using CliFx.Generators.Utils;
 using CliFx.Generators.Utils.Extensions;
 using Microsoft.CodeAnalysis;
 
-namespace CliFx.Generators;
+namespace CliFx.Generators.Binding;
 
-public partial class Generator
+internal static class CommandDescriptor
 {
     private static string EmitValidators(
         IReadOnlyList<INamedTypeSymbol> validatorTypes,
@@ -394,7 +393,7 @@ DiagnosticReporter diagnostics
                 false,
                 {{CSharp.Encode("Shows help text.")}},
                 new global::CliFx.Activation.BoolScalarInputConverter(),
-                global::System.Array.Empty<global::CliFx.Activation.InputValidator<bool>>()
+                global::System.Array.Empty<global::CliFx.Activation.IInputValidator<bool>>()
             )
             """;
     }
@@ -465,7 +464,7 @@ DiagnosticReporter diagnostics
                 false,
                 {{CSharp.Encode("Shows version information.")}},
                 new global::CliFx.Activation.BoolScalarInputConverter(),
-                global::System.Array.Empty<global::CliFx.Activation.InputValidator<bool>>()
+                global::System.Array.Empty<global::CliFx.Activation.IInputValidator<bool>>()
             )
             """;
     }
@@ -492,10 +491,7 @@ DiagnosticReporter diagnostics
             ),
         };
 
-    private static string EmitCommandDescriptor(
-        CommandSymbol command,
-        DiagnosticReporter diagnostics
-    ) =>
+    internal static string Emit(CommandSymbol command, DiagnosticReporter diagnostics) =>
         // lang=csharp
         $$"""
         // <auto-generated />

CliFx.Generators/Generator.cs …Generators/CommandDescriptorGenerator.csCliFx.Generators/Generator.cs renamed to CliFx.Generators/CommandDescriptorGenerator.cs CliFx.Generators/Generator.cs renamed to CliFx.Generators/CommandDescriptorGenerator.cs

@@ -12,7 +12,7 @@
 namespace CliFx.Generators;
 
 [Generator]
-public partial class Generator : IIncrementalGenerator
+public class CommandDescriptorGenerator : IIncrementalGenerator
 {
     public void Initialize(IncrementalGeneratorInitializationContext context)
     {
@@ -63,7 +63,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
                     var emitterDiagnostics = new List<Diagnostic>();
 
-                    var source = EmitCommandDescriptor(
+                    var source = CommandDescriptor.Emit(
                         item.Command,
                         new DiagnosticReporter(emitterDiagnostics)
                     );
@@ -107,7 +107,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
             {
                 ctx.AddSource(
                     "CommandRegistrations.g.cs",
-                    SourceText.From(EmitCommandRegistrations(commands), Encoding.UTF8)
+                    SourceText.From(CommandRegistration.Emit(commands), Encoding.UTF8)
                 );
             }
         );

…/Generator.CommandRegistrationEmitter.cs CliFx.Generators/CommandRegistration.csCliFx.Generators/Generator.CommandRegistrationEmitter.cs renamed to CliFx.Generators/CommandRegistration.cs CliFx.Generators/Generator.CommandRegistrationEmitter.cs renamed to CliFx.Generators/CommandRegistration.cs

@@ -8,9 +8,9 @@
 
 namespace CliFx.Generators;
 
-public partial class Generator
+internal static class CommandRegistration
 {
-    private static string EmitCommandRegistrations(IReadOnlyList<CommandSymbol> commands)
+    internal static string Emit(IReadOnlyList<CommandSymbol> commands)
     {
         var orderedCommands = commands.OrderBy(c => c.Name, StringComparer.Ordinal).ToArray();
 

CliFx.Generators/ProgramEntryPoint.cs

@@ -0,0 +1,32 @@
+namespace CliFx.Generators;
+
+internal static class ProgramEntryPoint
+{
+    internal static string Emit()
+    {
+        // lang=csharp
+        return """
+            // <auto-generated />
+            #nullable enable
+
+            namespace CliFx;
+
+            /// <summary>
+            /// Auto-generated entry point for the CliFx-based command-line application.
+            /// This class is emitted by the source generator when the project does not define
+            /// a <c>Main</c> method or top-level statements.
+            /// </summary>
+            public static class AutoGeneratedCommandLineProgram
+            {
+                /// <summary>
+                /// Builds and runs the command-line application using all commands detected in the current assembly.
+                /// </summary>
+                public static async global::System.Threading.Tasks.Task<int> Main() =>
+                    await new global::CliFx.CommandLineApplicationBuilder()
+                        .AddCommandsFromThisAssembly()
+                        .Build()
+                        .RunAsync();
+            }
+            """;
+    }
+}

CliFx.Generators/ProgramEntryPointGenerator.cs

@@ -0,0 +1,34 @@
+using System.Text;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Text;
+
+namespace CliFx.Generators;
+
+[Generator]
+public class ProgramEntryPointGenerator : IIncrementalGenerator
+{
+    public void Initialize(IncrementalGeneratorInitializationContext context)
+    {
+        var needsEntryPoint = context.CompilationProvider.Select(
+            static (compilation, cancellationToken) =>
+                (
+                    compilation.Options.OutputKind == OutputKind.ConsoleApplication
+                    || compilation.Options.OutputKind == OutputKind.WindowsApplication
+                ) && compilation.GetEntryPoint(cancellationToken) is null
+        );
+
+        context.RegisterSourceOutput(
+            needsEntryPoint,
+            static (ctx, needsEntryPoint) =>
+            {
+                if (!needsEntryPoint)
+                    return;
+
+                ctx.AddSource(
+                    "AutoGeneratedCommandLineProgram.g.cs",
+                    SourceText.From(ProgramEntryPoint.Emit(), Encoding.UTF8)
+                );
+            }
+        );
+    }
+}

CliFx.Tests/ApplicationSpecs.cs

@@ -7,6 +7,7 @@
 using CliFx.Tests.Utils.Extensions;
 using CliWrap;
 using FluentAssertions;
+using Microsoft.CodeAnalysis;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -49,6 +50,26 @@ public async Task I_can_create_an_application_with_a_custom_configuration()
         exitCode.Should().Be(0);
     }
 
+    [Fact]
+    public void I_can_create_an_application_without_a_configuration()
+    {
+        // Act
+        var commands = CommandCompiler.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public partial class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """,
+            OutputKind.ConsoleApplication
+        );
+
+        // Assert
+        commands[0].Type.Assembly.EntryPoint.Should().NotBeNull();
+    }
+
     [Fact(Timeout = 15000)]
     public async Task I_can_use_an_environment_variable_to_make_the_application_wait_for_the_debugger_to_attach()
     {

CliFx.Tests/Utils/CommandCompiler.cs

@@ -17,6 +17,7 @@ internal static class CommandCompiler
 {
     private static Compilation CreateCompilation(
         string sourceCode,
+        OutputKind outputKind,
         out IReadOnlyList<Diagnostic> diagnostics
     )
     {
@@ -63,14 +64,15 @@ out IReadOnlyList<Diagnostic> diagnostics
                 .Append(
                     MetadataReference.CreateFromFile(typeof(CommandCompiler).Assembly.Location)
                 ),
-            // DLL to avoid having to define the Main() method
-            new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
+            new CSharpCompilationOptions(outputKind)
         );
 
-        // Run the source generator
         CSharpGeneratorDriver
             .Create(
-                [new Generator().AsSourceGenerator()],
+                [
+                    new CommandDescriptorGenerator().AsSourceGenerator(),
+                    new ProgramEntryPointGenerator().AsSourceGenerator(),
+                ],
                 parseOptions: CSharpParseOptions.Default.WithLanguageVersion(
                     LanguageVersion.Preview
                 )
@@ -88,10 +90,11 @@ out var generatorDiagnostics
 
     public static IReadOnlyList<CommandDescriptor> Compile(
         string sourceCode,
+        OutputKind outputKind = OutputKind.DynamicallyLinkedLibrary,
         bool treatWarningsAsErrors = false
     )
     {
-        var compilation = CreateCompilation(sourceCode, out var diagnostics);
+        var compilation = CreateCompilation(sourceCode, outputKind, out var diagnostics);
 
         var compilationErrors = diagnostics
             .Where(d =>