Try some real madness

Author: ilevkivskyi

mypy/semanal_typeargs.py

@@ -33,8 +33,10 @@
     TypeVarTupleType,
     TypeVarType,
     UnboundType,
+    UnionType,
     UnpackType,
     flatten_nested_tuples,
+    flatten_nested_unions,
     get_proper_type,
     get_proper_types,
     split_with_prefix_and_suffix,
@@ -118,6 +120,10 @@ def visit_tuple_type(self, t: TupleType) -> None:
         # and we need to return an Instance instead of TupleType.
         super().visit_tuple_type(t)
 
+    def visit_union_type(self, t: UnionType) -> None:
+        super().visit_union_type(t)
+        t.items = flatten_nested_unions(t.items)
+
     def visit_callable_type(self, t: CallableType) -> None:
         super().visit_callable_type(t)
         t.normalize_trivial_unpack()

test-data/unit/check-redefine2.test

@@ -1395,3 +1395,30 @@ def test() -> None:
         y = li
     reveal_type(y)  # N: Revealed type is "builtins.list[Any]"
 [builtins fixtures/primitives.pyi]
+
+[case testNewRedefineNarrowingForNestedUnionWithAny]
+# flags: --allow-redefinition-new --local-partial-types
+from typing import Any, Union
+
+a: Any
+Int = Union[int, Any]
+
+def test(x: Union[str, Int]) -> None:
+    x = a
+    reveal_type(x)  # N: Revealed type is "Any"
+
+[case testNewRedefineWidenedArgumentDeferral]
+# flags: --allow-redefinition-new --local-partial-types
+def foo(x: int) -> None:
+    reveal_type(x)  # N: Revealed type is "builtins.int"
+    if bool():
+        x = "no"
+    c: C
+    c.x
+    reveal_type(x)  # N: Revealed type is "builtins.int | builtins.str"
+
+class C:
+    def __init__(self) -> None:
+        self.x = defer()
+
+def defer() -> int: ...