Description

Fixes #16843

Before

[CompilationMapping(SourceConstructFlags.Module)]
public static class @_
{
    [Serializable]
    [AttributeUsage(AttributeTargets.Struct)]
    [CompilationMapping(SourceConstructFlags.ObjectType)]
    public class CustomStructAttribute : Attribute
    {
    }


    [Serializable]
    [AttributeUsage(AttributeTargets.Class)]
    [CompilationMapping(SourceConstructFlags.ObjectType)]
    public class CustomClassAttribute : Attribute
    {
    }


    [Serializable]
    [CustomStruct]
    [CustomClass]
    [CompilationMapping(SourceConstructFlags.ObjectType)]
    public enum Color
    {
        Red,
        Green,
        Blue
    }
}

After

Error 842 "This attribute is not valid for use on this language element" should be reported.

Checklist

• Test cases added

• Performance benchmarks added in case of performance changes

• Release notes entry updated:

  Please make sure to add an entry with short succinct description of the change as well as link to this pull request to the respective release notes file, if applicable.

  Release notes files:

  • If anything under src/Compiler has been changed, please make sure to make an entry in docs/release-notes/.FSharp.Compiler.Service/<version>.md, where <version> is usually "highest" one, e.g. 42.8.200
  • If language feature was added (i.e. LanguageFeatures.fsi was changed), please add it to docs/releae-notes/.Language/preview.md
  • If a change to FSharp.Core was made, please make sure to edit docs/release-notes/.FSharp.Core/<version>.md where version is "highest" one, e.g. 8.0.200.

  Information about the release notes entries format can be found in the documentation.
  Example:

  • More inlines for Result module. (PR #16106)
  • Correctly handle assembly imports with public key token of 0 length. (Issue #16359, PR #16363)
    *while! (Language suggestion #1038, PR #14238)

  If you believe that release notes are not necessary for this PR, please add NO_RELEASE_NOTES label to the pull request.