Narrow issubclass to Never

Author: A5rocks

mypy/checker.py

@@ -8221,11 +8221,16 @@ def convert_to_typetype(type_map: TypeMap) -> TypeMap:
         t = typ
         if isinstance(t, TypeVarType):
             t = t.upper_bound
+
+        if isinstance(get_proper_type(t), UninhabitedType):
+            converted_type_map[expr] = UninhabitedType()
+            continue
         # TODO: should we only allow unions of instances as per PEP 484?
-        if not isinstance(get_proper_type(t), (UnionType, Instance, NoneType)):
+        elif not isinstance(get_proper_type(t), (UnionType, Instance, NoneType)):
             # unknown type; error was likely reported earlier
             return {}
         converted_type_map[expr] = TypeType.make_normalized(typ)
+
     return converted_type_map
 
 

test-data/unit/check-isinstance.test

@@ -1534,7 +1534,8 @@ from typing import Type, Sequence, Union
 
 x: Type[str]
 if issubclass(x, int):  # E: Subclass of "str" and "int" cannot exist: would have incompatible method signatures
-    reveal_type(x)  # N: Revealed type is "Type[builtins.str]"
+    reveal_type(x)  # E: Statement is unreachable \
+                    # N: Revealed type is "Never"
 
 class X: pass
 class Y(X): pass
@@ -1544,7 +1545,8 @@ a: Union[Type[Y], Type[Z]]
 if issubclass(a, X):
     reveal_type(a)  # N: Revealed type is "Union[Type[__main__.Y], Type[__main__.Z]]"
 else:
-    reveal_type(a)  # N: Revealed type is "Union[Type[__main__.Y], Type[__main__.Z]]"
+    reveal_type(a)  # E: Statement is unreachable \
+                    # N: Revealed type is "Never"
 [builtins fixtures/isinstancelist.pyi]
 
 [case testIssubclasDestructuringUnions1]
@@ -2668,7 +2670,8 @@ x: Type[A]
 if issubclass(x, B):
     reveal_type(x)        # N: Revealed type is "Type[__main__.<subclass of "__main__.A" and "__main__.B">]"
     if issubclass(x, C):  # E: Subclass of "A", "B", and "C" cannot exist: would have incompatible method signatures
-        reveal_type(x)    # N: Revealed type is "Type[__main__.<subclass of "__main__.A" and "__main__.B">]"
+        reveal_type(x)    # E: Statement is unreachable \
+                          # N: Revealed type is "Never"
     else:
         reveal_type(x)    # N: Revealed type is "Type[__main__.<subclass of "__main__.A" and "__main__.B">]"
 else:

test-data/unit/check-narrowing.test

@@ -1126,11 +1126,10 @@ T = TypeVar("T", A, B)
 
 def f(cls: Type[T]) -> T:
     if issubclass(cls, A):
-        reveal_type(cls)  # N: Revealed type is "Type[__main__.A]" \
-                          # N: Revealed type is "Type[__main__.B]"
+        reveal_type(cls)  # N: Revealed type is "Type[__main__.A]"
         x: bool
         if x:
-            return A()  # E: Incompatible return value type (got "A", expected "B")
+            return A()
         else:
             return B()  # E: Incompatible return value type (got "B", expected "A")
     assert False