Disallow TypeVar constraints parameterized by type variables

mypy/semanal.py

@@ -295,7 +295,7 @@
     type_vars_as_args,
 )
 from mypy.types_utils import is_invalid_recursive_alias, store_argument_type
-from mypy.typevars import fill_typevars
+from mypy.typevars import fill_typevars, has_no_typevars
 from mypy.util import correct_relative_import, is_dunder, module_prefix, unmangle, unnamed_function
 from mypy.visitor import NodeVisitor
 
@@ -5044,7 +5044,15 @@ def analyze_value_types(self, items: list[Expression]) -> list[Type]:
                     # soon, even if some value is not ready yet, see process_typevar_parameters()
                     # for an example.
                     analyzed = PlaceholderType(None, [], node.line)
-                result.append(analyzed)
+
+                # has_no_typevars does not work with PlaceholderType.
+                if not has_placeholder(analyzed) and not has_no_typevars(analyzed):
+                    self.fail(
+                        "TypeVar constraint type cannot be parametrized by type variables", node
+                    )
+                    result.append(AnyType(TypeOfAny.from_error))
+                else:
+                    result.append(analyzed)
             except TypeTranslationError:
                 self.fail("Type expected", node)
                 result.append(AnyType(TypeOfAny.from_error))

test-data/unit/semanal-errors.test

@@ -1060,6 +1060,19 @@ S = TypeVar('S', covariant=True, contravariant=True) \
     # E: TypeVar cannot be both covariant and contravariant
 [builtins fixtures/bool.pyi]
 
+[case testInvalidTypevarArgumentsGenericConstraint]
+from typing import Generic, List, TypeVar
+from typing_extensions import Self
+
+T = TypeVar("T")
+
+def f(x: T) -> None:
+    Bad = TypeVar("Bad", int, List[T])    # E: TypeVar constraint type cannot be parametrized by type variables
+class C(Generic[T]):
+    Bad = TypeVar("Bad", int, List[T])    # E: TypeVar constraint type cannot be parametrized by type variables
+class D:
+    Bad = TypeVar("Bad", int, List[Self]) # E: TypeVar constraint type cannot be parametrized by type variables
+
 [case testInvalidTypevarValues]
 from typing import TypeVar
 b = TypeVar('b', *[int]) # E: Unexpected argument to "TypeVar()"