[9.0-preview.5] Endpoint with nullable parameter no longer generates code with Request Delegate Generator

[martincostello]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Using version 9.0.100-preview.5.24272.3 of the .NET SDK from daily builds, an endpoint associated with a method that has a string[]? parameter is no longer having an endpoint generated an produces a RDG003 warning.

Error: /home/runner/work/adventofcode/adventofcode/src/AdventOfCode.Site/Program.cs(135,1): error RDG003: Unable to statically resolve parameter named 'arguments' for endpoint. Compile-time endpoint generation will skip this endpoint and the endpoint will be generated at runtime. For more information, please see https://aka.ms/aspnet/rdg-known-issues (https://learn.microsoft.com/aspnet/core/fundamentals/aot/request-delegate-generator/diagnostics/RDG003) [/home/runner/work/adventofcode/adventofcode/src/AdventOfCode.Site/AdventOfCode.Site.csproj]

The error is not generated with .NET 8 or .NET 9 preview 4.

The signature of the endpoint is the following (code):

internal static async Task<IResult> SolvePuzzleAsync(
    int year,
    int day,
    HttpRequest request,
    [FromForm] string[]? arguments,
    IFormFile? resource,
    PuzzleFactory factory,
    TimeProvider timeProvider,
    ILogger<Puzzle> logger,
    CancellationToken cancellationToken)

Expected Behavior

Request Delegate Generator successfully generates code for this endpoint.

Steps To Reproduce

1. Clone martincostello/adventofcode@fe22226#diff-f905acb7a057826fd183f2558445347c59e1cf0304dc0499d9f5e0ae4a523ebe
2. Run build.ps1 in the root of the repository.

Exceptions (if any)

No response

.NET Version

9.0.100-preview.5.24272.3

Anything else?

No response

[martincostello]

Looks like this was broken by #55465.

Specifically, this code addition:

aspnetcore/src/Http/Http.Extensions/gen/StaticRouteHandlerModel/EndpointParameter.cs

Lines 110 to 119 in 83573c7

	// Complex form binding is only supported in RDF because it uses shared source with Blazor that requires dynamic analysis
	// and codegen. Emit a diagnostic when these are encountered to avoid producing buggy code.
	else if (!(SymbolEqualityComparer.Default.Equals(Type, wellKnownTypes.Get(WellKnownType.Microsoft_Extensions_Primitives_StringValues))
	|| Type.SpecialType == SpecialType.System_String
	|| TryGetParsability(Type, wellKnownTypes, out var _)
	|| (IsArray && TryGetParsability(ElementType, wellKnownTypes, out var _))))
	{
	var location = endpoint.Operation.Syntax.GetLocation();
	endpoint.Diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.UnableToResolveParameterDescriptor, location, symbol.Name));
	}

[captainsafia]

@martincostello Thanks for reporting this bug and apologies for the delay as I work through my backlog here! 😅

I believe the reason this is happening is because the target type is a string[] in particular. The condition that you referenced above needs an additional (IsArray && ElementType.SpecialType == SpecialType.System_String) check since we don't don't generate a parsability method for string types out of TryGetParsability.

PR incoming....

[martincostello]

No problem - I did take a look at fixing it myself, but I wasn't sure if it was intentional or not so noped out of it 😅

Glad it's a quick fix!