Reorder branches in narrowing logic

Author: ilevkivskyi

mypy/meet.py

@@ -150,6 +150,10 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
         return make_simplified_union(
             [narrow_declared_type(declared, x) for x in narrowed.relevant_items()]
         )
+    elif isinstance(narrowed, UnionType):
+        return make_simplified_union(
+            [narrow_declared_type(declared, x) for x in narrowed.relevant_items()]
+        )
     elif (
         isinstance(declared, TypeVarType)
         and not has_type_vars(original_narrowed)
@@ -161,10 +165,6 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
             return UninhabitedType()
         else:
             return NoneType()
-    elif isinstance(narrowed, UnionType):
-        return make_simplified_union(
-            [narrow_declared_type(declared, x) for x in narrowed.relevant_items()]
-        )
     elif isinstance(narrowed, AnyType):
         return original_narrowed
     elif isinstance(narrowed, TypeVarType) and is_subtype(narrowed.upper_bound, declared):

test-data/unit/check-typeguard.test

@@ -777,3 +777,21 @@ def handle(model: Model) -> int:
         return process_model(model)
     return 0
 [builtins fixtures/tuple.pyi]
+
+[case testTypeGuardRestrictTypeVarUnion]
+from typing import Union, TypeVar
+from typing_extensions import TypeGuard
+
+class A:
+    x: int
+class B:
+    x: str
+
+def is_b(x: object) -> TypeGuard[B]: ...
+
+T = TypeVar("T")
+def test(x: T) -> T:
+    if isinstance(x, A) or is_b(x):
+        reveal_type(x.x)  # N: Revealed type is "Union[builtins.int, builtins.str]"
+    return x
+[builtins fixtures/isinstance.pyi]