From e7e3dfd6ce1374efbb16a90ac5cb7a3599ea54de Mon Sep 17 00:00:00 2001
From: 1ndahous3 <9205230+1ndahous3@users.noreply.github.com>
Date: Sun, 18 Oct 2026 17:00:18 +0300
Subject: [PATCH] Allow reflected fallback for in-place set operators (#9182)

Assisted-by: Codex:gpt-6
---
 crates/vm/src/builtins/set.rs       | 16 ++++++++++++----
 extra_tests/snippets/builtin_set.py | 16 ++++++++++++++++
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/crates/vm/src/builtins/set.rs b/crates/vm/src/builtins/set.rs
index 9c2255d00..f126ad318 100644
--- a/crates/vm/src/builtins/set.rs
+++ b/crates/vm/src/builtins/set.rs
@@ -1151,7 +1151,9 @@ impl AsNumber for PySet {
                 }
             }),
             inplace_subtract: Some(|a, b, vm| {
-                if let Some(a) = a.downcast_ref::<PySet>() {
+                if let Some(a) = a.downcast_ref::<PySet>()
+                    && PyRef::<PyAnySet>::check(b, vm)
+                {
                     PySet::__isub__(
                         a.to_owned(),
                         PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
@@ -1163,7 +1165,9 @@ impl AsNumber for PySet {
                 }
             }),
             inplace_and: Some(|a, b, vm| {
-                if let Some(a) = a.downcast_ref::<PySet>() {
+                if let Some(a) = a.downcast_ref::<PySet>()
+                    && PyRef::<PyAnySet>::check(b, vm)
+                {
                     PySet::__iand__(
                         a.to_owned(),
                         PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
@@ -1175,7 +1179,9 @@ impl AsNumber for PySet {
                 }
             }),
             inplace_xor: Some(|a, b, vm| {
-                if let Some(a) = a.downcast_ref::<PySet>() {
+                if let Some(a) = a.downcast_ref::<PySet>()
+                    && PyRef::<PyAnySet>::check(b, vm)
+                {
                     PySet::__ixor__(
                         a.to_owned(),
                         PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
@@ -1187,7 +1193,9 @@ impl AsNumber for PySet {
                 }
             }),
             inplace_or: Some(|a, b, vm| {
-                if let Some(a) = a.downcast_ref::<PySet>() {
+                if let Some(a) = a.downcast_ref::<PySet>()
+                    && PyRef::<PyAnySet>::check(b, vm)
+                {
                     PySet::__ior__(
                         a.to_owned(),
                         PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
diff --git a/extra_tests/snippets/builtin_set.py b/extra_tests/snippets/builtin_set.py
index 8e96a0959..19fab874b 100644
--- a/extra_tests/snippets/builtin_set.py
+++ b/extra_tests/snippets/builtin_set.py
@@ -1,3 +1,5 @@
+import operator
+
 from testutils import assert_raises
 
 assert set([1, 2]) == set([1, 2])
@@ -706,3 +708,17 @@ for use_operator in (False, True):
         intersection_target.intersection_update({1})
     assert not intersection_target
 assert intersection_events == [True, True]
+
+
+# Unsupported right operands must reach their reflected set operation.
+keys = {2: None, 3: None}.keys()
+for method, operation, expected in (
+    (set.__ior__, operator.ior, {1, 2, 3}),
+    (set.__iand__, operator.iand, {2}),
+    (set.__isub__, operator.isub, {1}),
+    (set.__ixor__, operator.ixor, {1, 3}),
+):
+    source = {1, 2}
+    assert method(source, keys) is NotImplemented
+    assert operation(source, keys) == expected
+    assert source == {1, 2}