add-codefix

name	add-codefix
description	Add a Roslyn CodeFixProvider (IDE lightbulb quick-fix) for an existing RASK0xx diagnostic. Use when a diagnostic has a single obvious mechanical fix. Implements the provider in src/Rask.Generators.CodeFixes, adds an apply-and-compare test in tests/Rask.Generators.Tests, notes the quick-fix in docs/diagnostics.md.

add-codefix

Quick-fixes live in src/Rask.Generators.CodeFixes — a SEPARATE assembly from Rask.Generators because code fixes reference Microsoft.CodeAnalysis.Workspaces, which an analyzer assembly must not (RS1038 / csc load failure). It contains no analyzers/generators, only CodeFixProviders, and is packed into analyzers/dotnet/cs/ by Rask.Server and Rask.Wasm (build-order-only ProjectReference, so -warnaserror is unaffected).

Only add a fix when there is ONE unambiguous mechanical edit. Skip diagnostics whose fix depends on intent (e.g. a Key: value) or context (e.g. removing a statement vs. an expression-lambda body).

1. Implement the provider

src/Rask.Generators.CodeFixes/{Name}CodeFixProvider.cs. Derive from the shared RaskCodeFixProvider<TNode> base (it owns the find-node/register/apply skeleton) — mirror ImgMissingAltCodeFixProvider / RequiredFactoryParamCodeFixProvider:

[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(FooCodeFixProvider))]
[Shared]
public sealed class FooCodeFixProvider : RaskCodeFixProvider<TNodeSyntax>
{
    public override ImmutableArray<string> FixableDiagnosticIds { get; } = ImmutableArray.Create("RASK0xx");
    protected override string Title => "…";
    protected override string EquivalenceKey => "RASK0xx_…";

    // Optional: withhold the fix when applying it would trade this diagnostic for a worse one
    // (e.g. RequiredFactoryParamCodeFixProvider suppresses when `required` would trip RASK002).
    protected override Task<bool> CanFixAsync(CodeFixContext context, TNodeSyntax node) => …;

    protected override Task<Document> FixAsync(Document document, TNodeSyntax node, CancellationToken ct) =>
        ReplaceNodeAsync(document, node, /* rewritten node */, ct);
}

The base finds the nearest enclosing TNode at the diagnostic span (analyzer diagnostics point at the flagged node; generator diagnostics like RASK001 point at the declaration via MakeLocation). Keep edits trivia-correct (e.g. a new modifier needs WithTrailingTrivia(Space)). Use CanFixAsync with the SemanticModel when the fix is only valid under some symbol condition.

2. Test it — tests/Rask.Generators.Tests/CodeFixProviderTests.cs

Use CodeFixHarness: ApplyAnalyzerFixAsync(analyzer, provider, "RASK0xx", source) for analyzer diagnostics, ApplyGeneratorFixAsync(generator, provider, "RASK0xx", source) for generator ones. Assert the rewritten text Contains the fixed form, covering each argument/declaration shape.

3. Document it — docs/diagnostics.md

Add the ID to the "IDE quick-fix" sentence in the intro, and append "(quick-fix available …)" to that diagnostic's Fix: line.

4. Finish

Run the rask-ship gate. Verify packaging survives: dotnet pack src/Rask.Server and confirm the codefix DLL is in analyzers/dotnet/cs/. The IDE lightbulb itself can only be smoke-tested manually — the unit tests prove the transform.