Revert dict.__or__ typeshed change (#21186)

Fixes #21141

I am not sure how typeshed patches work. If possible, I would add some
tests here, otherwise I will add tests in a follow-up PR.

Author: ilevkivskyi

misc/typeshed_patches/0001-Revert-dict.__or__-typeshed-change.patch

@@ -0,0 +1,30 @@
+From d88a4b774fc59ecd0f2d0fdda8e0e61092adafd3 Mon Sep 17 00:00:00 2001
+From: Ivan Levkivskyi <levkivskyi@gmail.com>
+Date: Wed, 8 Apr 2026 00:01:44 +0100
+Subject: [PATCH] Revert dict.__or__ typeshed change
+
+---
+ mypy/typeshed/stdlib/builtins.pyi | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/mypy/typeshed/stdlib/builtins.pyi b/mypy/typeshed/stdlib/builtins.pyi
+index 674142d70..25b21ba97 100644
+--- a/mypy/typeshed/stdlib/builtins.pyi
++++ b/mypy/typeshed/stdlib/builtins.pyi
+@@ -1142,7 +1142,13 @@ class dict(MutableMapping[_KT, _VT]):
+     def __reversed__(self) -> Iterator[_KT]: ...
+     __hash__: ClassVar[None]  # type: ignore[assignment]
+     def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
++    @overload
++    def __or__(self, value: dict[_KT, _VT], /) -> dict[_KT, _VT]: ...
++    @overload
+     def __or__(self, value: dict[_T1, _T2], /) -> dict[_KT | _T1, _VT | _T2]: ...
++    @overload
++    def __ror__(self, value: dict[_KT, _VT], /) -> dict[_KT, _VT]: ...
++    @overload
+     def __ror__(self, value: dict[_T1, _T2], /) -> dict[_KT | _T1, _VT | _T2]: ...
+     # dict.__ior__ should be kept roughly in line with MutableMapping.update()
+     @overload  # type: ignore[misc]
+-- 
+2.25.1
+

mypy/typeshed/stdlib/builtins.pyi

@@ -1142,7 +1142,13 @@ class dict(MutableMapping[_KT, _VT]):
     def __reversed__(self) -> Iterator[_KT]: ...
     __hash__: ClassVar[None]  # type: ignore[assignment]
     def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+    @overload
+    def __or__(self, value: dict[_KT, _VT], /) -> dict[_KT, _VT]: ...
+    @overload
     def __or__(self, value: dict[_T1, _T2], /) -> dict[_KT | _T1, _VT | _T2]: ...
+    @overload
+    def __ror__(self, value: dict[_KT, _VT], /) -> dict[_KT, _VT]: ...
+    @overload
     def __ror__(self, value: dict[_T1, _T2], /) -> dict[_KT | _T1, _VT | _T2]: ...
     # dict.__ior__ should be kept roughly in line with MutableMapping.update()
     @overload  # type: ignore[misc]

test-data/unit/pythoneval.test

@@ -2229,3 +2229,17 @@ def f(x: int, y: list[str]):
     x in y
 [out]
 _testStrictEqualityWithList.py:3: error: Non-overlapping container check (element type: "int", container item type: "str")
+
+[case testDictOrUnionEdgeCases]
+from typing import Mapping, Sequence, Union
+
+d: dict[str, list[str]]
+m: Mapping[str, Sequence[str]] = d | d
+
+A = dict[str, Union[A, int]]
+d1: A
+d2: A
+d3: A = d1 | d2
+reveal_type(d1 | d2)
+[out]
+_testDictOrUnionEdgeCases.py:10: note: Revealed type is "dict[str, dict[str, ... | int] | int]"