Additional TypeVar defaults validation

Author: cdce8p

mypy/checkexpr.py

@@ -5136,6 +5136,15 @@ def visit_temp_node(self, e: TempNode) -> Type:
         return e.type
 
     def visit_type_var_expr(self, e: TypeVarExpr) -> Type:
+        p_default = get_proper_type(e.default)
+        if not (
+            isinstance(p_default, AnyType)
+            and p_default.type_of_any == TypeOfAny.from_omitted_generics
+        ):
+            if not is_subtype(p_default, e.upper_bound):
+                self.chk.fail("TypeVar default must be a subtype of the bound type", e)
+            if e.values and not any(p_default == value for value in e.values):
+                self.chk.fail("TypeVar default must be one of the constraint types", e)
         return AnyType(TypeOfAny.special_form)
 
     def visit_paramspec_expr(self, e: ParamSpecExpr) -> Type:

test-data/unit/check-typevar-defaults.test

@@ -72,6 +72,15 @@ Ts2 = TypeVarTuple("Ts2", default=int)  # E: The default argument to TypeVarTupl
 Ts3 = TypeVarTuple("Ts3", default=Tuple[int])  # E: The default argument to TypeVarTuple must be an Unpacked tuple
 [builtins fixtures/tuple.pyi]
 
+[case testTypeVarDefaultsInvalid2]
+from typing import TypeVar, List, Union
+
+T1 = TypeVar("T1", bound=str, default=int)  # E: TypeVar default must be a subtype of the bound type
+T2 = TypeVar("T2", bound=List[str], default=List[int])  # E: TypeVar default must be a subtype of the bound type
+T3 = TypeVar("T3", int, str, default=bytes)  # E: TypeVar default must be one of the constraint types
+T4 = TypeVar("T4", int, str, default=Union[int, str])  # E: TypeVar default must be one of the constraint types
+T5 = TypeVar("T5", float, str, default=int)  # E: TypeVar default must be one of the constraint types
+
 [case testTypeVarDefaultsFunctions]
 from typing import TypeVar, ParamSpec, List, Union, Callable, Tuple
 from typing_extensions import TypeVarTuple, Unpack