Apply TypeVar defaults (functions)

Author: cdce8p

mypy/applytype.py

@@ -17,6 +17,7 @@
     TypeVarLikeType,
     TypeVarTupleType,
     TypeVarType,
+    UninhabitedType,
     UnpackType,
     get_proper_type,
 )
@@ -31,13 +32,15 @@ def get_target_type(
     context: Context,
     skip_unsatisfied: bool,
 ) -> Type | None:
+    p_type = get_proper_type(type)
+    if isinstance(p_type, UninhabitedType) and tvar.has_default():
+        return tvar.default
     if isinstance(tvar, ParamSpecType):
         return type
     if isinstance(tvar, TypeVarTupleType):
         return type
     assert isinstance(tvar, TypeVarType)
     values = tvar.values
-    p_type = get_proper_type(type)
     if values:
         if isinstance(p_type, AnyType):
             return type

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

@@ -71,3 +71,38 @@ Ts1 = TypeVarTuple("Ts1", default=2)  # E: TypeVarTuple "default" must be a type
 Ts2 = TypeVarTuple("Ts2", default=int)  # E: The default argument to TypeVarTuple must be an Unpacked tuple
 Ts3 = TypeVarTuple("Ts3", default=Tuple[int])  # E: The default argument to TypeVarTuple must be an Unpacked tuple
 [builtins fixtures/tuple.pyi]
+
+[case testTypeVarDefaultsFunctions]
+from typing import TypeVar, ParamSpec, List, Union, Callable, Tuple
+from typing_extensions import TypeVarTuple, Unpack
+
+T1 = TypeVar("T1", default=str)
+T2 = TypeVar("T2", bound=str, default=str)
+T3 = TypeVar("T3", bytes, str, default=str)
+P1 = ParamSpec("P1", default=(int, str))
+Ts1 = TypeVarTuple("Ts1", default=Unpack[Tuple[int, str]])
+
+def callback1(x: str) -> None: ...
+
+def func_a1(x: Union[int, T1]) -> T1: ...
+reveal_type(func_a1(2))  # N: Revealed type is "builtins.str"
+reveal_type(func_a1(2.1))  # N: Revealed type is "builtins.float"
+
+def func_a2(x: Union[int, T1]) -> List[T1]: ...
+reveal_type(func_a2(2))  # N: Revealed type is "builtins.list[builtins.str]"
+reveal_type(func_a2(2.1))  # N: Revealed type is "builtins.list[builtins.float]"
+
+def func_a3(x: Union[int, T2]) -> T2: ...
+reveal_type(func_a3(2))  # N: Revealed type is "builtins.str"
+
+def func_a4(x: Union[int, T3]) -> T3: ...
+reveal_type(func_a4(2))  # N: Revealed type is "builtins.str"
+
+def func_b1(x: Union[int, Callable[P1, None]]) -> Callable[P1, None]: ...
+reveal_type(func_b1(callback1))  # N: Revealed type is "def (x: builtins.str)"
+reveal_type(func_b1(2))  # N: Revealed type is "def (builtins.int, builtins.str)"
+
+def func_c1(x: Union[int, Callable[[Unpack[Ts1]], None]]) -> Tuple[Unpack[Ts1]]: ...
+# reveal_type(func_c1(callback1))  # Revealed type is "builtins.tuple[str]"  # TODO
+# reveal_type(func_c1(2))  # Revealed type is "builtins.tuple[builtins.int, builtins.str]"  # TODO
+[builtins fixtures/tuple.pyi]