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Merged
merged 15 commits into from
May 2, 2025
Merged

Move runtime async method validation into initial binding #78310

merged 15 commits into from
May 2, 2025

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333fred
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@333fred 333fred commented Apr 24, 2025 •
edited by jcouv
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We now do method construction and validation for runtime async helpers up front in initial binding, rather than doing it in RuntimeAsyncRewriter. I've also renamed the APIs as per dotnet/runtime#114310 (comment) (though I haven't added ConfigureAwait support yet, that will be the next PR). We now validate:

  • The helpers come from System.Runtime.CompilerServices.AsyncHelpers, defined in corelib. This means that I now need a fairly extensive corelib mock to be able to compile. When we have a testing runtime that defines these helpers, we can remove the giant mock and use the real one.
  • We properly error when expected helpers aren't present.
  • We properly check to make sure that constraints are satisfied when doing generic substitution in one of the runtime helpers.
  • Runtime async is not turned on if the async method does not return Task, Task<T>, ValueTask, or ValueTask<T>.

Relates to test plan #75960

@333fred 333fred requested a review from a team as a code owner April 24, 2025 23:39
@ghost ghost added Area-Compilers untriaged Issues and PRs which have not yet been triaged by a lead labels Apr 24, 2025
@333fred 333fred requested review from RikkiGibson and jcouv April 24, 2025 23:39
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src/Compilers/CSharp/Portable/Symbols/AssemblySymbol.cs
// Keep in sync with VB's AssemblySymbol.RuntimeSupportsAsyncMethods
internal bool RuntimeSupportsAsyncMethods
=> RuntimeSupportsFeature(SpecialMember.System_Runtime_CompilerServices_RuntimeFeature__Async)
|| _overrideRuntimeSupportsAsyncMethods;
=> GetSpecialType(InternalSpecialType.System_Runtime_CompilerServices_AsyncHelpers) is { TypeKind: TypeKind.Class, IsStatic: true };
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Should we remove the runtime feature entry from the design doc?

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What was the resolution?

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It was removed.

jcouv
jcouv reviewed Apr 25, 2025
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src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs
&& !ReferenceEquals(methodReturn, GetSpecialType(InternalSpecialType.System_Threading_Tasks_ValueTask))
&& !ReferenceEquals(methodReturn, GetSpecialType(InternalSpecialType.System_Threading_Tasks_ValueTask_T)))
{
return false;
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Is there a corresponding update to the design doc? Or should we have a follow-up comment to make the void-returning method scenario work at some point? #Pending

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Need to update the design doc, the runtime-side is very clear that only Task/ValueTask methods can be runtime async.

@jcouv jcouv self-assigned this Apr 25, 2025
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Done with review pass (iteration 10)

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333fred commented Apr 29, 2025

@jcouv addressed feedback. @RikkiGibson for review please

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LGTM Thanks (iteration 12). Consider updating the design doc (removing runtime feature flag) in same PR

@RikkiGibson RikkiGibson self-assigned this Apr 30, 2025
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It looks like the following tests need to be updated

Microsoft.CodeAnalysis.CSharp.UnitTests.MissingSpecialMember.AllWellKnownTypesBeforeCSharp7()
    in /_/src/Compilers/CSharp/Test/Symbol/Symbols/MissingSpecialMember.cs:line 926
Microsoft.CodeAnalysis.VisualBasic.UnitTests.Symbols.CorLibrary.CorTypes.PresentCorLib()
    in /_/src/Compilers/VisualBasic/Test/Symbol/SymbolsTests/CorLibrary/CorTypes.vb:line 77

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333fred commented Apr 30, 2025

LGTM Thanks (iteration 12). Consider updating the design doc (removing runtime feature flag) in same PR

The doc is maintained in main.

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src/Compilers/CSharp/Portable/BoundTree/BoundAwaitableInfo.cs
break;

default:
Debug.Fail($"Unexpected RuntimeAsyncAwaitMethod: {RuntimeAsyncAwaitMethod.Name}");
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@RikkiGibson RikkiGibson Apr 30, 2025 •
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Checking my understanding: it looks like we expect this condition to never occur. i.e. compiler will never produce a BoundAwaitableInfo whose RuntimeAsyncAwaitMethod.Name is not one of the above cases.

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Yep, that's correct.

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LGTM with some minor comments/suggestions

src/Compilers/CSharp/Portable/Binder/Binder_Await.cs Outdated
return false;
}

Debug.Assert((runtimeAwaitHelper is { Arity: 1 } && maybeResultType is { }) || runtimeAwaitHelper.TypeParameters.Length == 0);
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nit: maybe slightly more uniform/compact check would be:

Suggested change
Debug.Assert((runtimeAwaitHelper is { Arity: 1 } && maybeResultType is { }) || runtimeAwaitHelper.TypeParameters.Length == 0);
Debug.Assert(runtimeAwaitHelper.Arity == (maybeResultType is null ? 0 : 1));

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TypeWithAnnotations also has its own HasType which distinguishes default values from "meaningful" values, which could be used instead of System.Nullable, but, there's no deep need to do that.

src/Compilers/CSharp/Portable/Binder/Binder_Await.cs
@@ -286,7 +302,90 @@ private bool GetAwaitableExpressionInfo(
TypeSymbol awaiterType = getAwaiter.Type!;
return GetIsCompletedProperty(awaiterType, node, expression.Type!, diagnostics, out isCompleted)
&& AwaiterImplementsINotifyCompletion(awaiterType, node, diagnostics)
&& GetGetResultMethod(getAwaiter, node, expression.Type!, diagnostics, out getResult, out getAwaiterGetResultCall);
&& GetGetResultMethod(getAwaiter, node, expression.Type!, diagnostics, out getResult, out getAwaiterGetResultCall)
&& (!isRuntimeAsyncEnabled || getRuntimeAwaitAwaiter(awaiterType, out runtimeAsyncAwaitMethod, expression.Syntax, diagnostics));
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Checking my understanding on the sequence of checks here.

  • if runtime async, and got runtime await helper, use that
  • otherwise, need an "ordinary" GetAwaiterMethod to proceed--if we didn't get one just return false.
  • then check for IsCompleted, GetResult, ..
  • finally if runtime async enabled, then get a RuntimeAwaitAwaiter?

Is the idea that in the 'RuntimeAwaitAwaiter' case, we still need to use the type's GetAwaiter method etc? That seems to make sense.

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Is the idea that in the 'RuntimeAwaitAwaiter' case, we still need to use the type's GetAwaiter method etc?

Precisely. This the lowering mechanism in https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Runtime%20Async%20Design.md#await-any-other-type, as opposed to the rest of the document which talks about await Task

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs Outdated
}

var methodReturn = method.ReturnType.OriginalDefinition;
if (!ReferenceEquals(methodReturn, GetSpecialType(InternalSpecialType.System_Threading_Tasks_Task))
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It would be nice if there a way to say something like methodReturn.InternalSpecialType is InternalSpecialType.Task or Task_T or ValueTask or ValueTask_T. No need to try and dig up a way to do that though.

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Actually, I think we can, since this is special types, not well-known types.

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333fred commented Apr 30, 2025

@jcouv @RikkiGibson for another look, a few small changes in the last commit.

AlekseyTs
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333fred commented May 2, 2025

@jcouv, since the last 2 commits were only minor changes, I'm going to go ahead and merge this now; if you have any comments on these last 2 bits, I can address them in the next PR.

@333fred 333fred merged commit e272201 into dotnet:features/runtime-async May 2, 2025
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@333fred 333fred deleted the initial-binding-validation branch May 2, 2025 17:37
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