[RuntimeAsync] Treat calls to async helpers in non-async callers as invalid IL

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@jakobbotsch is already working on this.

Since Apr 17, 2026.

  • #130397 by @copilot-swe-agent — open

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Description

area-CodeGen-coreclr runtime-async

Re: https://github.com/dotnet/runtime/pull/118045/files#r2233249240

It is possible to construct IL where calls to non-task-returning async methods like AsyncHelpers.Await happen in nonasync callers. It is unlikely that this can work correctly in some random method. It is better if JIT refuses to compile calls to non-task returning async methods if the calee is not async.

One caveat - we may have a few places in the implementation of async itself (like in async thunks) where this practice is legal because the code explicitly arranges handling for suspension/continuations. That would need to be allowed.

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