[API Proposal]: adding C# option to the [StringSyntaxAttribute]

[HakamFostok]

Background and motivation

It would be very helpful for the source generator scenario if we had a StringSyntax for C#:

1. syntax error checking
2. code completion inside strings

API Proposal

namespace System.Diagnostics.CodeAnalysis;

public sealed class StringSyntaxAttribute : Attribute
{
    public const string CSharp = "C#";
}

API Usage

using System.Diagnostics.CodeAnalysis;

public class Class 
{
	[StringSyntax(StringSyntaxAttribute.CSharp)]
   	public string? CodeForSourceGenerator = " ... c# code here";
}

Alternative Designs

No response

Risks

No response

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• [API Proposal]: C#/VB support in StringSyntaxAttribute. #65708

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[JakeYallop]

As a workaround, there is an undocumented "C#-test" language that adds syntax highlighting for C#.

using System.Diagnostics.CodeAnalysis;

public class Class 
{
	[StringSyntax("C#-test")]
   	public string? CodeForSourceGenerator = " ... c# code here";
}

[ufcpp]

There is a PR two weeks ago: dotnet/roslyn#81558

[HakamFostok]

@ufcpp Thanks a lot
But in the PR there is no link to original issue or documentation.
When can I use this feature?
Is it already in .NET 10?
Or should we wait to .NET 11?
Also, the PR has the 'vscode' tag, and it is in the Roysln repo not in the dotnet repo.
I think the PR mentioned is not related to [StringSyntax] attribute, but maybe it will have the same effect

[HakamFostok]

@JakeYallop Yes, it worked, but why the -test suffix after the C#?
And why is there is constant yet for it in the StringSyntax class?

[JakeYallop]

Its C#-test I think is because it also supports highlighting the test markup used when writing unit tests for analyzers (which was how I originally became aware of its existence), which isn't technically valid C#:

dotnet/roslyn#75181 (comment)