added patch for __radd__

Author: randolf-scholz

mypy/checkexpr.py

@@ -111,6 +111,7 @@
 from mypy.semanal_enum import ENUM_BASES
 from mypy.state import state
 from mypy.subtypes import (
+    covers_at_runtime,
     find_member,
     is_equivalent,
     is_same_type,
@@ -4048,14 +4049,20 @@ def lookup_definer(typ: Instance, attr_name: str) -> str | None:
 
             variants_raw = [(op_name, left_op, left_type, right_expr)]
         elif (
-            is_subtype(right_type, left_type)
-            and isinstance(left_type, Instance)
-            and isinstance(right_type, Instance)
-            and not (
-                left_type.type.alt_promote is not None
-                and left_type.type.alt_promote.type is right_type.type
+            # Note: use covers_at_runtime instead of is_subtype.
+            #    fixes https://github.com/python/mypy/issues/19006
+            covers_at_runtime(right_type, left_type)
+            and (
+                not (isinstance(left_type, Instance) and isinstance(right_type, Instance))
+                or (
+                    (
+                        left_type.type.alt_promote is None
+                        or left_type.type.alt_promote.type is not right_type.type
+                    )
+                    and lookup_definer(left_type, op_name)
+                    != lookup_definer(right_type, rev_op_name)
+                )
             )
-            and lookup_definer(left_type, op_name) != lookup_definer(right_type, rev_op_name)
         ):
             # When we do "A() + B()" where B is a subclass of A, we'll actually try calling
             # B's __radd__ method first, but ONLY if B explicitly defines or overrides the

test-data/unit/check-expressions.test

@@ -681,6 +681,29 @@ class B:
 s: str
 s = A() + B() # E: Unsupported operand types for + ("A" and "B")
 
+[case testReverseBinaryOperator4]
+
+from typing import assert_type, Never
+
+class Size(tuple[int, ...]):
+    def __add__(self, other: tuple[int, ...], /) -> "Size": return Size()
+    def __radd__(self, other: tuple[int, ...], /) -> "Size": return Size()
+
+size: Size = Size([3, 4])
+tup0: tuple[()] = ()
+tup1: tuple[int] = (1,)
+tup2: tuple[int, int] = (1, 2)
+tupN: tuple[int, ...] = (1, 2, 3)
+tupX: tuple[Never, ...] = ()
+
+assert_type(tup0 + size, Size)
+assert_type(tup1 + size, Size)
+assert_type(tup2 + size, Size)
+assert_type(tupN + size, Size)
+assert_type(tupX + size, Size)
+
+[builtins fixtures/tuple.pyi]
+
 [case testBinaryOperatorWithAnyRightOperand]
 from typing import Any, cast
 class A: pass