Add OpenAPI/Swagger support for minimal actions

[halter73]

Addresses #30662

[pranavkm]

Interesting q - MVC does add an entry for items that do not specify a method constraint (with a null value), so maybe it's fine to add one:

aspnetcore/src/Mvc/Mvc.ApiExplorer/src/DefaultApiDescriptionProvider.cs

Lines 341 to 351 in 44bcd96

	private IEnumerable<string?> GetHttpMethods(ControllerActionDescriptor action)
	{
	if (action.ActionConstraints != null && action.ActionConstraints.Count > 0)
	{
	return action.ActionConstraints.OfType<HttpMethodActionConstraint>().SelectMany(c => c.HttpMethods);
	}
	else
	{
	return new string?[] { null };
	}
	}

[halter73]

I tried null initially since ApiDescription.HttpMethod is indeed nullable, but I get this when trying this with Swashbuckle 5.6.3.

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Ambiguous HTTP method for action - . Actions require an explicit HttpMethod binding for Swagger/OpenAPI 3.0
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperations(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository) in Swashbuckle.AspNetCore.SwaggerGen.dll:token 0x60000f0+0x76
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePaths(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository) in Swashbuckle.AspNetCore.SwaggerGen.dll:token 0x60000ef+0x60
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwagger(String documentName, String host, String basePath) in Swashbuckle.AspNetCore.SwaggerGen.dll:token 0x60000ed+0xe0
         at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider) in Swashbuckle.AspNetCore.Swagger.dll:token 0x6000009+0xa9
         at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application) in Microsoft.AspNetCore.Server.Kestrel.Core.dll:token 0x6000a9f+0x1b8

Is there a workaround?

[bradygaster]

OH SO EXCITING

[halter73]

@jaredpar Is there a better way to do this?

[ghost]

Thank you for submitting this for API review. This will be reviewed by @dotnet/aspnet-api-review at the next meeting of the ASP.NET Core API Review group. Please ensure you take a look at the API review process documentation and ensure that:

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[halter73]

/backport to release/6.0-preview6

[github-actions]

Started backporting to release/6.0-preview6: https://github.com/dotnet/aspnetcore/actions/runs/941202939

[BrennanConroy]

API Review:
AddMinimalActionsApiExplorer()

That would make MinimalActions more of a public name, whereas right now it's mostly a code-name.

AddEndpointsApiExplorer() uses the now overloaded word "Endpoints" and it doesn't apply to all Endpoints.