【C#】Incremental Source Generator入門

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<TargetFramework>netstandard2.0</TargetFramework>
		<ImplicitUsings>enable</ImplicitUsings>
		<Nullable>enable</Nullable>

	    <!-- 最新の言語バージョンを明示的に指定 -->
		<LangVersion>13</LangVersion>

	    <!-- SourceGeneratorを動作させるための設定 -->
		<IsRoslynComponent>true</IsRoslynComponent>
		<AnalyzerLanguage>cs</AnalyzerLanguage>

	    <!-- NuGet配布用の設定 -->
		<IncludeBuildOutput>false</IncludeBuildOutput>
		<DevelopmentDependency>true</DevelopmentDependency>
		<IncludeSymbols>false</IncludeSymbols>
		<SuppressDependenciesWhenPacking>true</SuppressDependenciesWhenPacking>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.3.0" />
	</ItemGroup>

	<!-- NuGetパッケージの出力先をanalyzers/dotnet/csに -->
	<ItemGroup>
		<None Include="$(OutputPath)\$(AssemblyName).dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
	</ItemGroup>

</Project>

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<OutputType>Exe</OutputType>
		<TargetFramework>net8.0</TargetFramework>
		<ImplicitUsings>enable</ImplicitUsings>
		<Nullable>enable</Nullable>
	</PropertyGroup>

	<ItemGroup>
        <!-- Source Generatorのプロジェクトのパス -->
		<ProjectReference Include="..">
			<OutputItemType>Analyzer</OutputItemType>
			<ReferenceOutputAssembly>false</ReferenceOutputAssembly>
		</ProjectReference>
	</ItemGroup>

</Project>

{
    "profiles": {
        "Sample.SourceGenerator": {
            "commandName": "DebugRoslynComponent",
            "targetProject": "../../ConsoleApp1/ConsoleApp1.csproj"
        }
    }
}

using Microsoft.CodeAnalysis;

namespace HelloGenerator;

[Generator(LanguageNames.CSharp)]
public class HelloSourceGenerator : IIncrementalGenerator
{
    public void Initialize(IncrementalGeneratorInitializationContext context)
    {
    }
}

public void Initialize(IncrementalGeneratorInitializationContext context)
{
    context.RegisterPostInitializationOutput(static initContext =>
    {
        // 名前の競合でエラーが起こることが多々あるので、明示的にglobal::からクラス名を書いておく
        var source = $$"""
// <auto-generated/>

namespace HelloGenerator
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Class, AllowMultiple = false)]
    internal sealed class GenerateHelloAttribute : global::System.Attribute
    {
    }
}
""";

        // 第1引数に渡すhintNameはGeneratorごとに一意である必要がある
        context.AddSource("GenerateHelloAttribute.g.cs", source);
    });
}

using HelloGenerator;

[GenerateHello] // GenerateHelloAttributeが生成されている
public partial class Foo
{
}

public void Initialize(IncrementalGeneratorInitializationContext context)
{
    ...

    // 名前で指定された属性に対するIncrementalValuesProviderを作成する
    var provider = context.SyntaxProvider.ForAttributeWithMetadataName(
        "HelloGenerator.GenerateHelloAttribute",         // 対象の属性のフルネーム
        static (node, cancellationToken) => true,        // predicate, 追加でフィルタリングを行いたければこのラムダ式で
        static (context, cancellationToken) => context); // transform, GeneratorAttributeSyntaxContextから必要な情報に加工する(今回はcontextをそのまま利用する)
}

public void Initialize(IncrementalGeneratorInitializationContext context)
{
    ...

    // 長くなるのでメソッドに分離しておくと良い
    provider.RegisterSourceOutput(source, Emit);
}

static void Emit(SourceProductionContext context, GeneratorAttributeSyntaxContext attributeContext)
{
    // GeneratorAttributeSyntaxContextから対象のSymbolとSyntaxNodeを取得できる
    var typeSymbol = (INamedTypeSymbol)attributeContext.TargetSymbol;
    var typeNode = (TypeDeclarationSyntax)attributeContext.TargetNode;

    // namespace部分 (UnityのC# 9.0に対応する場合はfile scoped namespaceを使わない)
    var nsBegin = typeSymbol.ContainingNamespace.IsGlobalNamespace
        ? ""
        : $"namespace {typeSymbol.ContainingNamespace} \{";
    var nsEnd = typeSymbol.ContainingNamespace.IsGlobalNamespace
        ? ""
        : "}";

    // 型をファイル名として利用するためのエスケープ処理
    var fullType = typeSymbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat)
        .Replace("global::", "")
        .Replace("<", "_")
        .Replace(">", "_");

    // 生成コードを作成
    // auto-generatedタグや警告の抑止はテンプレ
    var sourceCode = $$"""
// <auto-generated/>

#nullable enable
#pragma warning disable CS8600
#pragma warning disable CS8601
#pragma warning disable CS8602
#pragma warning disable CS8603
#pragma warning disable CS8604

{{nsBegin}}

    partial class {{typeSymbol.Name}}
    {
        public void Hello()
        {
            global::System.Console.WriteLine("Hello, this is {{typeSymbol.Name}}!");
        }
    }

{{nsEnd}}

""";

    // AddSourceでコードを生成
    context.AddSource($"{fullType}.Hello.g.cs", sourceCode);
}

using HelloGenerator;

var foo = new Foo();
foo.Hello(); // Hello, this is Foo!

[GenerateHello]
public partial class Foo
{
}

public static class DiagnosticDescriptors
{
    public const string Id = "HELLO"
    public const string Category = "HelloGenerator";

    public static readonly DiagnosticDescriptor MustBePartial = new(
        id: Id + "001",
        title: "GenerateHello class must be partial",
        messageFormat: "The GenerateHello class '{0}' must be partial",
        category: Category,
        defaultSeverity: DiagnosticSeverity.Error,
        isEnabledByDefault: true);

    public static readonly DiagnosticDescriptor MustNotBeNested = new(
        id: Id + "002",
        title: "GenerateHello class must not be nested",
        messageFormat: "The GenerateHello class '{0}' must not be nested",
        category: Category,
        defaultSeverity: DiagnosticSeverity.Error,
        isEnabledByDefault: true);

    public static readonly DiagnosticDescriptor ExistsHello = new(
        id: Id + "003",
        title: "Hello method",
        messageFormat: "The GenerateHello class '{0}' has Hello method but it is not allowed",
        category: Category,
        defaultSeverity: DiagnosticSeverity.Error,
        isEnabledByDefault: true);
}

static void Emit(SourceProductionContext context, GeneratorAttributeSyntaxContext attributeContext)
{
    var typeSymbol = (INamedTypeSymbol)attributeContext.TargetSymbol;
    var typeNode = (TypeDeclarationSyntax)attributeContext.TargetNode;

    var hasError = false;

    // partialキーワードがない場合
    if (!typeNode.Modifiers.Any(m => m.IsKind(SyntaxKind.PartialKeyword)))
    {
        context.ReportDiagnostic(Diagnostic.Create(
            DiagnosticDescriptors.MustBePartial,
            typeNode.Identifier.GetLocation(),
            typeSymbol.Name));
        
        hasError = true;
    }

    // 型がネストされている場合
    if (typeNode.Parent is TypeDeclarationSyntax)
    {
        context.ReportDiagnostic(Diagnostic.Create(
            DiagnosticDescriptors.MustNotBeNested,
            typeNode.Identifier.GetLocation(),
            typeSymbol.Name));
        
        hasError = true;
    }

    // Helloメソッドが既に定義されている場合
    if (typeSymbol.GetMembers("Hello").Length != 0)
    {
        context.ReportDiagnostic(Diagnostic.Create(
            DiagnosticDescriptors.ExistsHello,
            typeNode.Identifier.GetLocation(),
            typeSymbol.Name));

        hasError = true;
    }

    // エラーがあるなら生成を中止
    if (hasError)
    {
        return;
    }

    ...
}

var attributeProvider = context.SyntaxProvider
    .ForAttributeWithMetadataName(...);

// CompilationProvider(後述)と組み合わせる
var provider = attributeProvider.Combine(context.CompilationProvider);

var config = context.AdditionalTextsProvider.Select((text, ct) =>
    {
        if (text.Path.EndsWith("Sample.json")) return text.GetText(ct);
        return null;
    })
    .Where(x => x != null)
    .Collect();

<Project Sdk="Microsoft.NET.Sdk">

<PropertyGroup>
   <SampleSourceGenerator_Experimental>enable</SampleSourceGenerator_Experimental>
</PropertyGroup>

<ItemGroup>
   <CompilerVisibleProperty Include="SampleSourceGenerator_Experimental" />
</ItemGroup>

var config = context.AnalyzerConfigOptionsProvider
    .Select((options, _) =>
        {
            // 接頭辞にbuild_property.が必要なことに注意
            var experimentalEnabled = options.GlobalOptions.TryGetValue("build_property.SampleSourceGenerator_Experimental", out var experimentalEnabledValue)
                && experimentalEnabledValue == "enable";

            ...
        });

var hasDependencyInjection = context.MetadataReferencesProvider
    .Collect()
    .Select((xs, _) =>
    {
        var hasDependencyInjection = false;

        foreach (var x in xs)
        {
            var name = x.Display;
            if (name == null) continue;

            if (!hasDependencyInjection && name.EndsWith("Microsoft.Extensions.DependencyInjection.dll"))
            {
                hasDependencyInjection = true;
                continue;
            }

            // etc...
        }

        ...
    });

var parseOptions = context.ParseOptionsProvider.Select((parseOptions, ct) =>
{
    var csOptions = (CSharpParseOptions)parseOptions;
    var langVersion = csOptions.LanguageVersion;
    var net7 = csOptions.PreprocessorSymbolNames.Contains("NET7_0_OR_GREATER");
    return (langVersion, net7);
});

var runMethod = context.SyntaxProvider
    .CreateSyntaxProvider((node, ct) =>
    {
        // メソッド呼び出しを解析 (InvocationExpression)
        if (node.IsKind(SyntaxKind.InvocationExpression))
        {
            var invocationExpression = (node as InvocationExpressionSyntax);
            if (invocationExpression == null) return false;

            var expr = invocationExpression.Expression as MemberAccessExpressionSyntax;

            // App.Run()メソッド呼び出しのみを取得
            if ((expr?.Expression as IdentifierNameSyntax)?.Identifier.Text == "App")
            {
                var methodName = expr?.Name.Identifier.Text;
                if (methodName is "Run")
                {
                    return true;
                }
            }

            return false;
        }

        return false;
    }, (context, ct) => context);

// こんな感じで、必要なデータを単一のrecordにまとめておく
record MethodData
{
    public required bool IsStatic { get; init; }
    public required bool IsAsync { get; init; }
    public required bool HasReturnValue { get; init; }
    ...
}

var provider = context.SyntaxProvider
    .ForAttributeWithMetadataName(
        "SampleAttribute",
        static (node, ct) => true,
        static (context, ct) => context)
    .Combine(context.CompilationProvider)
    .WithComparer(Comparer.Instance);