gistfile1.txt

from __future__ import annotations
from mypy.plugin import Plugin, ClassDefContext

class MyPlugin(Plugin):
    def get_base_class_hook(self, fullname: str) -> None:
        if fullname == "..." or "..." in fullname:
        
            # debug print:
            print( "hook added" )
        
            return self.my_hook
        return None
        
    OR PERHAPS:
        
    def get_class_decorator_hook(self, fullname: str) -> None:
        if fullname == "..." or "..." in fullname:
            return self.my_hook
        return None

    def my_hook(self, ctx: ClassDefContext) -> None:
        if ctx.cls.info...:  # Some condition that is forbidden
            ctx.api.fail(
                ctx=ctx.cls.info,
                msg="some error message" )

        # Perhaps you might need something like that:
        for decorator in ctx.cls.decorators:
            if decorator.callee.fullname == "...":
                ...

def plugin(version: str):
    return MyPlugin