Enable trimming for OpenAPI package

[captainsafia]

Part of #54598.

• Use RDG to source generate the MapOpenApi endpoint
• Use STJ source generation for (de)serialization
• Add RUC/RDC attributes where required
• Fix bug where RDG would emit code for complex form bound parameters

[BrennanConroy]

This sounds like it's blaming blazor for dynamic codegen? Does that mean we can make it work by splitting from blazor?

[captainsafia]

Minimal APIs shares the same implementation that Blazor uses for complex form binding (see here) which uses reflection. We could implement a source gen layer for form binding but the plan has been to do that in conjunction with Blazor so we're not solving the same problem twice in different ways.

[eerhardt]

You shouldn't need the extra field. You can simply add [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] to the parameter, and it will work.

internal sealed class TypeBasedOpenApiDocumentTransformer([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type transformerType) : IOpenApiDocumentTransformer
{
    private readonly ObjectFactory _transformerFactory = ActivatorUtilities.CreateFactory(transformerType, []);

    public async Task TransformAsync(OpenApiDocument document, OpenApiDocumentTransformerContext context, CancellationToken cancellationToken)
    {
        var transformer = _transformerFactory.Invoke(context.ApplicationServices, []) as IOpenApiDocumentTransformer;
        Debug.Assert(transformer != null, $"The type {transformerType} does not implement {nameof(IOpenApiDocumentTransformer)}.");

[captainsafia]

I tried this but I believe there's an issue at the intersection of primary constructors + linker + DAM attributes:

Trim analysis warning IL2077: Microsoft.AspNetCore.OpenApi.TypeBasedOpenApiDocumentTransformer.TypeBasedOpenApiDocumentTransformer(Type): 'instanceType' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors' in call to 'Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateFactory(Type, Type[])'. The field 'Microsoft.AspNetCore.OpenApi.TypeBasedOpenApiDocumentTransformer.<_transformerType>P' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.

[eerhardt]

That sounds like a great issue to open. 😄

[captainsafia]

See dotnet/runtime#101861

[eerhardt]

Suggested change

	<IsTrimmable>true</IsTrimmable>
	<IsAotCompatible>true</IsAotCompatible>

We should use this property which will enable all the analzyers. (honestly I thought that's what TrimmableProjects.props was supposed to be doing...?)

[captainsafia]

From my understanding, TrimmableProjects allows us to explicitly define the list of projects that the LinkabilityChecker will run against. This MSBuild check keeps the TrimmableProjects.props and IsTrimmable flags in sync.

As for IsAotCompatible, I could've sworn there was some MSBuild that was bringing in a PackageReference and borking the build althoug that doesn't seem to to be the case.

Edit: it's PublishAoT that brings in the PackageReference not PublishAoT.

[eerhardt]

Just a few minor comments. It would be good to log that ILLink Roslyn Analyzer issue. I'll bet more people will run into it with primary constructors becoming popular.

[captainsafia]

Just a few minor comments. It would be good to log that ILLink Roslyn Analyzer issue. I'll bet more people will run into it with primary constructors becoming popular.

Yep, I'm working on getting a minimal repro with this. Just running the linker on a console project with the buggy scenario doesn't reproduce so I suspect that something about the way our LinkabilityChecker is configured is causing the problem here.