Check typevar defaults with is_same_type instead of full equality

Author: sterliakov

mypy/checker.py

@@ -2658,7 +2658,7 @@ def check_typevar_defaults(self, tvars: Sequence[TypeVarLikeType]) -> None:
                 continue
             if not is_subtype(tv.default, tv.upper_bound):
                 self.fail("TypeVar default must be a subtype of the bound type", tv)
-            if tv.values and not any(tv.default == value for value in tv.values):
+            if tv.values and not any(is_same_type(tv.default, value) for value in tv.values):
                 self.fail("TypeVar default must be one of the constraint types", tv)
 
     def check_enum(self, defn: ClassDef) -> None:

mypy/checkexpr.py

@@ -6210,7 +6210,7 @@ def visit_type_var_expr(self, e: TypeVarExpr) -> Type:
         ):
             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):
+            if e.values and not any(is_same_type(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)
 

test-data/unit/check-python312.test

@@ -2042,3 +2042,15 @@ tuple[*tuple[int, ...], *tuple[int, ...]]  # E: More than one Unpack in a type i
 b: tuple[*tuple[int, ...], *tuple[int, ...]]  # E: More than one Unpack in a type is not allowed
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]
+
+[case testPEP695TypeVarDefaultAliases]
+from typing_extensions import TypeVar
+
+type K = int
+type V = int
+type L = list[int]
+
+T1 = TypeVar("T1", str, K, default=K)
+T2 = TypeVar("T2", str, K, default=V)
+T3 = TypeVar("T3", str, L, default=L)
+[builtins fixtures/tuple.pyi]

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

@@ -729,8 +729,6 @@ class C(Generic[_I]): pass
 t: type[C] | int = C
 [builtins fixtures/tuple.pyi]
 
-
-
 [case testGenericTypeAliasWithDefaultTypeVarPreservesNoneInDefault]
 from typing_extensions import TypeVar
 from typing import Generic, Union
@@ -749,3 +747,36 @@ MyA = A[T1, int]
 a: MyA = A(None, 10)
 reveal_type(a.a)  # N: Revealed type is "Union[builtins.int, None]"
 [builtins fixtures/tuple.pyi]
+
+[case testTypeVarDefaultAliasesTypeAliasType]
+from typing_extensions import TypeAliasType, TypeVar
+
+K = TypeAliasType("K", int)
+V = TypeAliasType("V", int)
+L = TypeAliasType("L", list[int])
+T1 = TypeVar("T1", str, K, default=K)
+T2 = TypeVar("T2", str, K, default=V)
+T3 = TypeVar("T3", str, L, default=L)
+[builtins fixtures/tuple.pyi]
+
+[case testTypeVarDefaultAliasesImplicitAlias]
+from typing_extensions import TypeVar
+
+K = int
+V = int
+L = list[int]
+T1 = TypeVar("T1", str, K, default=K)
+T2 = TypeVar("T2", str, K, default=V)
+T3 = TypeVar("T3", str, L, default=L)
+[builtins fixtures/tuple.pyi]
+
+[case testTypeVarDefaultAliasesExplicitAlias]
+from typing_extensions import TypeAlias, TypeVar
+
+K: TypeAlias = int
+V: TypeAlias = int
+L: TypeAlias = list[int]
+T1 = TypeVar("T1", str, K, default=K)
+T2 = TypeVar("T2", str, K, default=V)
+T3 = TypeVar("T3", str, L, default=L)
+[builtins fixtures/tuple.pyi]