builtins: return Union type for list.__add__

Author: hauntsaninja

stdlib/2/__builtin__.pyi

@@ -658,8 +658,10 @@ class list(MutableSequence[_T], Generic[_T]):
     def __getslice__(self, start: int, stop: int) -> List[_T]: ...
     def __setslice__(self, start: int, stop: int, o: Sequence[_T]) -> None: ...
     def __delslice__(self, start: int, stop: int) -> None: ...
-    def __add__(self, x: List[_T]) -> List[_T]: ...
-    def __iadd__(self: _S, x: Iterable[_T]) -> _S: ...
+    def __add__(self, x: List[_S]) -> List[Union[_T, _S]]: ...
+    def __iadd__(self, x: Iterable[_S]) -> List[Union[_T, _S]]: ...
+    # Workaround https://github.com/python/mypy/issues/5971
+    def __radd__(self, x: List[_S]) -> List[Union[_T, _S]]: ...
     def __mul__(self, n: int) -> List[_T]: ...
     def __rmul__(self, n: int) -> List[_T]: ...
     def __contains__(self, o: object) -> bool: ...

stdlib/2/builtins.pyi

@@ -658,8 +658,10 @@ class list(MutableSequence[_T], Generic[_T]):
     def __getslice__(self, start: int, stop: int) -> List[_T]: ...
     def __setslice__(self, start: int, stop: int, o: Sequence[_T]) -> None: ...
     def __delslice__(self, start: int, stop: int) -> None: ...
-    def __add__(self, x: List[_T]) -> List[_T]: ...
-    def __iadd__(self: _S, x: Iterable[_T]) -> _S: ...
+    def __add__(self, x: List[_S]) -> List[Union[_T, _S]]: ...
+    def __iadd__(self, x: Iterable[_S]) -> List[Union[_T, _S]]: ...
+    # Workaround https://github.com/python/mypy/issues/5971
+    def __radd__(self, x: List[_S]) -> List[Union[_T, _S]]: ...
     def __mul__(self, n: int) -> List[_T]: ...
     def __rmul__(self, n: int) -> List[_T]: ...
     def __contains__(self, o: object) -> bool: ...

stdlib/3/builtins.pyi

@@ -726,8 +726,10 @@ class list(MutableSequence[_T], Generic[_T]):
     @overload
     def __setitem__(self, s: slice, o: Iterable[_T]) -> None: ...
     def __delitem__(self, i: Union[int, slice]) -> None: ...
-    def __add__(self, x: List[_T]) -> List[_T]: ...
-    def __iadd__(self: _S, x: Iterable[_T]) -> _S: ...
+    def __add__(self, x: List[_S]) -> List[Union[_T, _S]]: ...
+    def __iadd__(self, x: Iterable[_S]) -> List[Union[_T, _S]]: ...
+    # Workaround https://github.com/python/mypy/issues/5971
+    def __radd__(self, x: List[_S]) -> List[Union[_T, _S]]: ...
     def __mul__(self, n: int) -> List[_T]: ...
     def __rmul__(self, n: int) -> List[_T]: ...
     def __imul__(self: _S, n: int) -> _S: ...

tests/stubtest_whitelists/py3_common.txt

@@ -41,6 +41,7 @@ builtins.classmethod.__get__
 builtins.complex.__complex__
 builtins.ellipsis
 builtins.function
+builtins.list.__radd__
 builtins.memoryview.__contains__
 builtins.memoryview.__iter__
 builtins.memoryview.cast