Zomp.MethodCloning

Zomp.MethodCloning

The plumbing for source generators that copy a method and change it.

Copying a method into a generated file sounds easy until the copy has to compile there. This package handles that part, so your generator only contains the change you actually want to make.

It powers Zomp.SyncMethodGenerator, which turns async methods into sync ones, and Zomp.MethodCloning.Variants, which replaces T4 templates.

What you get

Piece	Does
CloneTarget	Finds the methods your attribute marks, on the method or its type
MethodLocation	Collects the namespaces, usings and partial types the copy needs
CloningRewriter	Fully qualifies every name, so the copy compiles anywhere
ClonedMethodOutput	Names the files, catches colliding copies and adds the output

You derive from CloningRewriter, override what you change, and use its MapSymbol, MapTypeName and MapMemberName hooks to substitute types and names.

A whole generator, sketched

[Generator]
public sealed class CopyGenerator : IIncrementalGenerator
{
    public void Initialize(IncrementalGeneratorInitializationContext context)
    {
        var copies = CloneTarget.ForAttribute(context.SyntaxProvider, "My.CopyAttribute")
            .Select(static (target, ct) => Copy(target)!)
            .Where(static copy => copy is not null);

        ClonedMethodOutput.Register(context, copies, MyDiagnostics.Collision);
    }

    private static ClonedMethod? Copy(CloneTarget target)
    {
        var symbol = (IMethodSymbol)target.Context.TargetSymbol;
        if (!MethodLocation.TryCreate(target.Syntax, symbol, out var location, out var root))
        {
            return null;
        }

        var copy = new RenameRewriter(target.Context.SemanticModel, target.Syntax).Visit(root);
        return ClonedMethod.Create(location, target.Syntax, copy, nullableDisabled: false, ImmutableArray<ReportedDiagnostic>.Empty);
    }
}

internal sealed class RenameRewriter(SemanticModel model, MethodDeclarationSyntax method)
    : CloningRewriter(model, method)
{
    public override SyntaxNode? VisitMethodDeclaration(MethodDeclarationSyntax node)
        => base.VisitMethodDeclaration(node) is MethodDeclarationSyntax copy
            ? copy.WithIdentifier(SyntaxFactory.Identifier(node.Identifier.ValueText + "Copy"))
            : null;
}

Install

<PackageReference Include="Zomp.MethodCloning" PrivateAssets="all" />

It ships as source: the files compile into your generator as internal types. There is no DLL to bundle into analyzers/, and two generators can never disagree about its version.

Requirements

• C# 12 or later in the generator project.
• On netstandard2.0, PolySharp for polyfills such as IsExternalInit.
• Roslyn 4.8 or later. Define ROSLYN_4_12_OR_GREATER or ROSLYN_5_0_OR_GREATER when you compile against those, to get the newer code paths.