Handle X[T] - X[Any]

Author: brianschubert

mypy/subtypes.py

@@ -1953,6 +1953,8 @@ def restrict_subtype_away(t: Type, s: Type, *, consider_runtime_isinstance: bool
         return UninhabitedType()
     elif is_proper_subtype(t, s, ignore_promotions=True):
         return UninhabitedType()
+    elif is_proper_subtype(t, s, ignore_promotions=True, erase_instances=True):
+        return UninhabitedType()
     else:
         return t
 

test-data/unit/check-typeis.test

@@ -134,16 +134,41 @@ def main(a: object) -> None:
         reveal_type(a)  # N: Revealed type is "Union[builtins.int, builtins.str]"
 [builtins fixtures/tuple.pyi]
 
-[case testTypeIsUnionOfGenerics]
-from typing import List, Union
+[case testTypeIsUnionWithGeneric]
+from typing import Any, List, Sequence, Union
 from typing_extensions import TypeIs
-def is_foo(a: Union[List[int], List[str]]) -> TypeIs[List[str]]: pass
-def main(a: Union[List[int], List[str]]) -> None:
-    if is_foo(a):
+
+def is_int_list(a: object) -> TypeIs[List[int]]: pass
+def is_int_seq(a: object) -> TypeIs[Sequence[int]]: pass
+def is_seq(a: object) -> TypeIs[Sequence[Any]]: pass
+
+def f1(a: Union[List[int], List[str]]) -> None:
+    if is_int_list(a):
+        reveal_type(a)  # N: Revealed type is "builtins.list[builtins.int]"
+    else:
         reveal_type(a)  # N: Revealed type is "builtins.list[builtins.str]"
+    reveal_type(a)  # N: Revealed type is "Union[builtins.list[builtins.int], builtins.list[builtins.str]]"
+
+def f2(a: Union[List[int], int]) -> None:
+    if is_int_list(a):
+        reveal_type(a)  # N: Revealed type is "builtins.list[builtins.int]"
     else:
+        reveal_type(a)  # N: Revealed type is "builtins.int"
+    reveal_type(a)  # N: Revealed type is "Union[builtins.list[builtins.int], builtins.int]"
+
+def f3(a: Union[List[bool], List[str]]) -> None:
+    if is_int_seq(a):
+        reveal_type(a)  # N: Revealed type is "builtins.list[builtins.bool]"
+    else:
+        reveal_type(a)  # N: Revealed type is "builtins.list[builtins.str]"
+    reveal_type(a)  # N: Revealed type is "Union[builtins.list[builtins.bool], builtins.list[builtins.str]]"
+
+def f4(a: Union[List[int], int]) -> None:
+    if is_seq(a):
         reveal_type(a)  # N: Revealed type is "builtins.list[builtins.int]"
-    reveal_type(a)  # N: Revealed type is "Union[builtins.list[builtins.int], builtins.list[builtins.str]]"
+    else:
+        reveal_type(a)  # N: Revealed type is "builtins.int"
+    reveal_type(a)  # N: Revealed type is "Union[builtins.list[builtins.int], builtins.int]"
 [builtins fixtures/tuple.pyi]
 
 [case testTypeIsNonzeroFloat]