Type parameters are not in scope in class decorators

mypy/semanal.py

@@ -1814,8 +1814,18 @@ def analyze_class(self, defn: ClassDef) -> None:
             defn.info.is_protocol = is_protocol
             self.recalculate_metaclass(defn, declared_metaclass)
             defn.info.runtime_protocol = False
+
+            if defn.type_args:
+                # PEP 695 type parameters are not in scope in class decorators, so
+                # temporarily disable type parameter namespace.
+                type_params_names = self.locals.pop()
+                self.scope_stack.pop()
             for decorator in defn.decorators:
                 self.analyze_class_decorator(defn, decorator)
+            if defn.type_args:
+                self.locals.append(type_params_names)
+                self.scope_stack.append(SCOPE_ANNOTATION)
+
             self.analyze_class_body_common(defn)
 
     def setup_type_vars(self, defn: ClassDef, tvar_defs: list[TypeVarLikeType]) -> None:

test-data/unit/check-python312.test

@@ -1149,3 +1149,15 @@ class C[T]:
 
 def f[S, S](x: S) -> S:  # E: "S" already defined as a type parameter
     return x
+
+[case testPEP695ClassDecorator]
+# mypy: enable-incomplete-feature=NewGenericSyntax
+from typing import Any
+
+T = 0
+
+def decorator(x: str) -> Any: ...
+
+@decorator(T)  # E: Argument 1 to "decorator" has incompatible type "int"; expected "str"
+class C[T]:
+    pass