CS9270 'InterceptsLocationAttribute(string, int, int)' is not supported when using net8.0 Request Delegate Generator

[eerhardt]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When using the latest C# / Visual Studio main builds with a net8.0 minimal API project with <EnableRequestDelegateGenerator>true</EnableRequestDelegateGenerator>, you now get a warning:

Severity	Code	Description	Project	File	Line	Suppression State	Details
Warning (active)	CS9270	'InterceptsLocationAttribute(string, int, int)' is not supported. Move to 'InterceptableLocation'-based generation of these attributes instead. (https://github.com/dotnet/roslyn/issues/72133)	WebApplication6	D:\source\WebApplication6\WebApplication6\obj\Debug\net8.0\Microsoft.AspNetCore.Http.RequestDelegateGenerator\Microsoft.AspNetCore.Http.RequestDelegateGenerator.RequestDelegateGenerator\GeneratedRouteBuilderExtensions.g.cs	61		

See dotnet/roslyn#76641 for more discussion.

Expected Behavior

There shouldn't be any warnings by default.

Steps To Reproduce

0. Install the latest C# or Visual Studio from main. I have C# Tools 4.13.0-3.24620.4+98ea496177bc8e607dbf454abd6b5a5e4678aed2
1. Create a new "ASP.NET Core Web API" project. Be sure to select ".NET 8.0 (LongTerm Support)"
2. Modify the .csproj with <EnableRequestDelegateGenerator>true</EnableRequestDelegateGenerator>
3. Build

Note: You can get the same with creating a new "ASP.NET Core Web API (native AOT)" project.

Exceptions (if any)

No response

.NET Version

No response

Anything else?

cc @captainsafia @mikekistler

[captainsafia]

@eerhardt Thanks for flagging this.

I had made the change to support the check-sum based InterceptsLocation attribute in .NET 9 but it hadn't crossed my mind that we need to change 8.0 as well for scenarios where folks are building a .NET 8 project against a newer compiler.

I assume it's safe to backport the .NET 9 change to .NET 8 and we don't need to worry about back-combat with older versions of the compiler.

@RikkiGibson Can you confirm if that is the case?

[RikkiGibson]

I am thinking it is best to not backport the checksum-based solution to the net8.0 generator, under the assumption that compilers from either the .NET 8 or .NET 9 SDKs could be used to build projects that use those generators. So calling those new APIs while maintaining .NET 8 SDK compatibility might require reflection + fallback to the "old way", or something like that.

I am resolving dotnet/roslyn#76641 by ensuring the "not supported" warning is only reported when the user's project targets net9.0 or later. Is targeting net9.0 sufficient to ensure that at minimum a "net9.0" generator will be used?

[captainsafia]

Is targeting net9.0 sufficient to ensure that at minimum a "net9.0" generator will be used?

Yep, we package the source generator in the shared framework so the checksum-based interceptor is only emitted when you target a net9.0 TFM.

[eerhardt]

CS9270 'InterceptsLocationAttribute(string, int, int)' is not supported when using Microsoft.Extensions.Configuration.Binder 8.0.x (dotnet/roslyn#76641) was resolved by the C# compiler to no longer emit the warning when targeting net8.0. This can now be closed as there isn't anything we need to do in ASP.NET core.