ASP0016 False positive for nested anonymous methods #64173
Description
You can add the following test to RequestDelegateReturnTypeAnalyzerTests.cs:
[Fact]
public async Task AnonymousDelegate_RequestDelegate_ReturnType_InNestedAynonymousDelegate_DoesNotReportDiagnostics()
{
await VerifyCS.VerifyAnalyzerAsync(@"
using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
var webApp = WebApplication.Create();
webApp.Run((context) =>
{
Func<Task<DateTime>> _ = () => Task.FromResult(DateTime.Now);
return Task.CompletedTask;
});
");
}And you'll get the following failure:
Message:
System.InvalidOperationException : Mismatch between number of diagnostics returned, expected "0" actual "1"
Diagnostics:
// /0/Test0.cs(6,12): warning ASP0016: The method used to create a RequestDelegate returns Task<System.DateTime>. RequestDelegate discards this value. If this isn't intended then change the return type to non-generic Task or, if the delegate is a route handler, cast it to Delegate so the return value is written to the response.
VerifyCS.Diagnostic().WithSpan(6, 12, 10, 2).WithArguments("System.DateTime"),
Stack Trace:
DefaultVerifier.Equal[T](T expected, T actual, String message)
AnalyzerTest`1.VerifyDiagnosticResults(IEnumerable`1 actualResults, ImmutableArray`1 analyzers, DiagnosticResult[] expectedResults, IVerifier verifier)
AnalyzerTest`1.VerifyDiagnosticsAsync(EvaluatedProjectState primaryProject, ImmutableArray`1 additionalProjects, DiagnosticResult[] expected, IVerifier verifier, CancellationToken cancellationToken)
AnalyzerTest`1.RunImplAsync(CancellationToken cancellationToken)
AnalyzerTest`1.RunAsync(CancellationToken cancellationToken)
CSharpAnalyzerVerifier`1.VerifyAnalyzerAsync(String source, DiagnosticResult[] expected) line 46
RequestDelegateReturnTypeAnalyzerTests.AnonymousDelegate_RequestDelegate_ReturnType_InNestedAynonymousDelegate_DoesNotReportDiagnostics() line 73
--- End of stack trace from previous location ---
This is incorrect because the Task<System.DateTime> is not being returned directly from the anonymous RequestDelegate, but instead an inner anonymous method which is not a RequestDelegate. This was uncovered by #64120 which resulted in the following line getting incorrectly flagged by ASP0016 even though the lambda calling UpgradeAsync() and returning a Task<Stream> was being passed to ThrowsAsync as a Func<Task<Stream>> and was never converted to a RequestDelegate.
D:\a\_work\1\s\src\Servers\IIS\IIS\test\testassets\InProcessWebSite\Startup.WebSockets.cs(98,17): error ASP0016: The method used to create a RequestDelegate returns Task<System.IO.Stream>. RequestDelegate discards this value. If this isn't intended then change the return type to non-generic Task or, if the delegate is a route handler, cast it to Delegate so the return value is written to the response. (https://aka.ms/aspnet/analyzers) [D:\a\_work\1\s\src\Servers\IIS\IIS\test\testassets\InProcessNewShimWebSite\InProcessNewShimWebSite.csproj::TargetFramework=net8.0]
##[error]src\Servers\IIS\IIS\test\testassets\InProcessWebSite\Startup.WebSockets.cs(98,17): error ASP0016: (NETCORE_ENGINEERING_TELEMETRY=Build) The method used to create a RequestDelegate returns Task<System.IO.Stream>. RequestDelegate discards this value. If this isn't intended then change the return type to non-generic Task or, if the delegate is a route handler, cast it to Delegate so the return value is written to the response. (https://aka.ms/aspnet/analyzers)