The Dart specification says:

Metadata can appear before a library, part header, class, typedef, type parameter, constructor, factory, function, parameter, or variable declaration, and before an import, export, or part directive.

This is also the way it's implemented, such that

class A<@Annotation T> {}

is valid code.

However, TargetKind lacks any value that may represent this case.

I propose creating a TargetKind.typeParameter to fulfill this necessity.