adjust branch statement in checker.py, modify testcase

Author: TH3CHARLie

mypy/checker.py

@@ -3730,6 +3730,9 @@ def find_isinstance_check(self, node: Expression
                 if literal(expr) == LITERAL_TYPE:
                     vartype = get_proper_type(type_map[expr])
                     type = get_isinstance_type(node.args[1], type_map)
+                    if (isinstance(vartype, TypeVarType)):
+                        vartype = vartype.upper_bound
+                    vartype = get_proper_type(vartype)
                     if isinstance(vartype, UnionType):
                         union_list = []
                         for t in get_proper_types(vartype.items):
@@ -3745,8 +3748,6 @@ def find_isinstance_check(self, node: Expression
                     elif (isinstance(vartype, Instance) and
                             vartype.type.fullname() == 'builtins.type'):
                         vartype = self.named_type('builtins.object')
-                    elif (isinstance(vartype, TypeVarType)):
-                        vartype = vartype.upper_bound
                     else:
                         # Any other object whose type we don't know precisely
                         # for example, Any or a custom metaclass.

test-data/unit/check-classes.test

@@ -6518,22 +6518,21 @@ from typing import TypeVar, Generic
 
 TypeT = TypeVar("TypeT", bound=type)
 
-class IntBase:
+class Base:
     field: int = 42
 
-class IntFoo(Generic[TypeT]):
-    def method(self, other: TypeT) -> int:
-        if issubclass(other, IntBase):
+class C1:
+    def method(self, other: type) -> int:
+        if issubclass(other, Base):
+            reveal_type(other)  # N: Revealed type is 'Type[__main__.Base]'
             return other.field
         return 0
 
-class StrBase:
-    field: str = "hello"
-
-class StrFoo(Generic[TypeT]):
-    def method(self, other: TypeT) -> str:
-        if issubclass(other, StrBase):
+class C2(Generic[TypeT]):
+    def method(self, other: TypeT) -> int:
+        if issubclass(other, Base):
+            reveal_type(other)  # N: Revealed type is 'Type[__main__.Base]'
             return other.field
-        return "hi"
+        return 0
 
 [builtins fixtures/isinstancelist.pyi]