Razor grammar missing some token/scopes and causing theme weirdness

[timheuer]

@maddymontaquila cloned issue microsoft/vscode-dotnettools#2078 on 2025-06-10:

Describe the Issue

The lambda is showing up as red with an underline, but it is working fine, and there are no errors in the Problems window or when I hover over it. Lightbulb just suggests "Wrap attribute"

Steps To Reproduce

Using an internal codebase - can share offline

Expected Behavior

No response

Environment Information

MacOS
Insiders VS Code
Previews of devkit (1.30.4) + C# (2.81.17)

Razor "Force Runtime Code Generation" "Use New Formatting Engine" are both turned on

[timheuer]

@JakeRadMSFT commented on 2025-06-11:

I believe this is razor? :)

[timheuer]

@timheuer commented on 2025-06-12:

I believe this might be a theming thing. It's not a red squiggle so no problem to report. I cannot repro this either on the codebase. Waiting for @maddymontaquila to tell me what theme she's using to validate similarly my hypothesis that this is not a lang issue actually.

e.g Dracula theme has underlining in this lambda and the => arrow as well does Monokai theme:

[timheuer]

@timheuer commented on 2025-06-12:

Did some more looking into this. Looking at the token/scope the language is recognized as aspnetcorerazor and thus the rules are applied from that. It looks like the textmate grammar provided by vscode (which may be a copy from razor) does not have a definition for these experiences like C# does (see: https://github.com/dotnet/razor/blob/main/src/Razor/src/Microsoft.VisualStudio.RazorExtension/EmbeddedGrammars/aspnetcorerazor.tmLanguage.json missing a definition like https://github.com/dotnet/csharp-tmLanguage/blob/main/grammars/csharp.tmLanguage.cson#L1406).

Some themes clearly have provided some styling here and others have not. A root 'fix' might be to ensure the VSCode grammar has the correct definitions perhaps coming from https://github.com/dotnet/vscode-csharp/blob/main/src/razor/syntaxes/aspnetcorerazor.tmLanguage.json

(moving this bug there)

[dibarbet]

For some reason I thought that the Razor grammar embedded the C# grammar (and hence wouldn't have an arrow definition defined in the aspnetcore textmate definition).

But that does not seem to be the case (unless its configured differently) - https://github.com/dotnet/vscode-csharp/blob/main/package.json#L5543. If it isn't, that is definitely something that should be looked at, as otherwise the C# textmate grammar in Razor is always going to be lacking.