Fix #3777: decompile runtime async without a separate C# 15 setting#3791
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Runtime async is a compiler feature that emits ordinary async/await (a C# 5 construct), so reconstructing it should not require selecting C# 15. The dedicated RuntimeAsync setting was also redundant: AsyncAwaitDecompiler already runs the runtime-async transforms only when AsyncAwait is enabled. Fold the behavior into the AsyncAwait setting and drop the separate toggle. Assisted-by: Claude:claude-opus-4-8:Claude Code
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Fixes #3777.
Runtime async is a compiler feature, not a language feature: there is no
dotnet/csharplangspec for it, and Roslyn emits it even in older language versions when enabled. ILSpy decompiles runtime-async methods back into ordinaryasync/await, which is a C# 5 construct. Gating that reconstruction on C# 15 needlessly produced worse output whenever a lower language version was selected.Rather than just re-gate the toggle to C# 5, this removes the standalone
RuntimeAsyncsetting entirely and folds its behavior into the existingAsyncAwait("Decompile async methods") setting. The separate toggle was redundant:AsyncAwaitDecompiler.Runalready early-returns whenAsyncAwaitis disabled, so the runtime-async transforms were always nested inside that gate. Runtime async now follows the single async/await toggle, exactly like state-machine async.Changes
RuntimeAsyncproperty fromDecompilerSettings(plus its C# 15 version-gating inSetLanguageVersion/GetMinimumRequiredVersion) and its resource string.DecompilerTypeSystem.GetOptions,AsyncAwaitDecompiler,EarlyExpressionTransforms) throughAsyncAwait.Notes
RuntimeAsyncattribute in saved settings is silently ignored on load; no migration needed.Testing
RuntimeAsync*pretty tests locally (RuntimeAsync,RuntimeAsyncForeach,RuntimeAsyncMain,RuntimeAsyncStreams,RuntimeAsyncUsing,RuntimeAsyncCustomTaskType): all 12 cases pass.