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Siegfried Pammer
0da83059a1
C# 10 allows [AsyncMethodBuilder(typeof(...))] directly on an async method (also on local functions and explicit-return-type lambdas) to override the builder that the return type's canonical builder would otherwise dictate. The fixture covers overrides returning Task, Task<T>, ValueTask and ValueTask<T> (via the BCL pooling builders), struct vs class builders, an open-generic builder on a generic method, capture of this, await-free bodies, awaits in loops, a local function and a lambda. The test is Assert.Ignore'd because AsyncAwaitDecompiler rejects any state machine whose Start call's builder type differs from the builder derived from the return type (TaskType.IsNonGenericTaskType/ IsGenericTaskType), so every overridden method decompiles as a raw kickoff body plus the untransformed MoveNext state machine, which does not recompile. The method-level attribute itself is correctly preserved in metadata output; only the async-transform recognition is missing. All four Roslyn 4.14/latest debug/opt configs compile the fixture and fail only at the output comparison. The builder scaffolding in the fixture is verbatim ILSpy output (verified by decompiling a probe assembly), so only the async method bodies are the desired-output spec. Assisted-by: Claude:claude-fable-5:Claude Code