Avoid widening to Any for checks like type(x) is type(y: Any) (#20663)

Author: hauntsaninja

mypy/checker.py

@@ -6830,6 +6830,13 @@ def narrow_type_by_identity_equality(
                 expr = operands[j]
 
                 current_type_range = self.get_isinstance_type(expr)
+                if current_type_range is not None:
+                    target_type = make_simplified_union([tr.item for tr in current_type_range])
+                    if isinstance(target_type, AnyType):
+                        # Avoid widening to Any for checks like `type(x) is type(y: Any)`.
+                        # We patch this here because it is desirable to widen to any for cases like
+                        # isinstance(x, (y: Any))
+                        continue
                 if_map, else_map = conditional_types_to_typemaps(
                     expr_in_type_expr,
                     *self.conditional_types_with_intersection(

test-data/unit/check-narrowing.test

@@ -3094,6 +3094,28 @@ z: Any
 if int == type(z) == int:
     reveal_type(z) # N: Revealed type is "builtins.int"
 
+[case testTypeEqualsCheckWidening]
+# flags: --strict-equality --warn-unreachable
+from typing import Any
+
+def f(x: str, y: Any, z: object):
+    if type(x) is type(y):
+        reveal_type(x) # N: Revealed type is "builtins.str"
+        reveal_type(y) # N: Revealed type is "builtins.str"
+
+    if type(x) == type(y):
+        reveal_type(x) # N: Revealed type is "builtins.str"
+        reveal_type(y) # N: Revealed type is "builtins.str"
+
+    if type(x) is type(z):
+        reveal_type(x) # N: Revealed type is "builtins.str"
+        reveal_type(z) # N: Revealed type is "builtins.str"
+
+    if type(x) == type(z):
+        reveal_type(x) # N: Revealed type is "builtins.str"
+        reveal_type(z) # N: Revealed type is "builtins.str"
+[builtins fixtures/primitives.pyi]
+
 [case testTypeEqualsCheckUsingIs]
 # flags: --strict-equality --warn-unreachable
 from typing import Any
@@ -3130,20 +3152,6 @@ def main(x: Union[B, C]):
         reveal_type(x)  # N: Revealed type is "__main__.B | __main__.C"
 [builtins fixtures/isinstance.pyi]
 
-[case testTypeEqualsCheckUsingImplicitTypes-xfail]
-from typing import Any
-
-x: str
-y: Any
-z: object
-if type(y) is type(x):
-    reveal_type(x) # N: Revealed type is "builtins.str"
-    reveal_type(y) # N: Revealed type is "builtins.str"
-
-if type(x) is type(z):
-    reveal_type(x) # N: Revealed type is "builtins.str"
-    reveal_type(z) # N: Revealed type is "builtins.str"
-
 [case testTypeEqualsCheckUsingDifferentSpecializedTypes]
 # flags: --warn-unreachable
 from collections import defaultdict