Issue #26020: Fix evaluation order for set literals

Lib/test/test_set.py

@@ -360,6 +360,21 @@ class TestSet(TestJointOps):
         t = self.thetype(s)
         self.assertNotEqual(id(s), id(t))
 
+    def test_set_literal_insertion_order(self):
+        # SF Issue #26020 -- Expect left to right insertion
+        s = {1, 1.0, True}
+        self.assertEqual(len(s), 1)
+        stored_value = s.pop()
+        self.assertEqual(type(stored_value), int)
+
+    def test_set_literal_evaluation_order(self):
+        # Expect left to right expression evaluation
+        events = []
+        def record(obj):
+            events.append(obj)
+        s = {record(1), record(2), record(3)}
+        self.assertEqual(events, [1, 2, 3])
+
     def test_hash(self):
         self.assertRaises(TypeError, hash, self.s)
 

Python/ceval.c

@@ -2477,14 +2477,16 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 
         TARGET(BUILD_SET)
         {
+            int i;
             x = PySet_New(NULL);
             if (x != NULL) {
-                for (; --oparg >= 0;) {
-                    w = POP();
+                for (i = oparg; i > 0; i--) {
+                    w = PEEK(i);
                     if (err == 0)
                         err = PySet_Add(x, w);
                     Py_DECREF(w);
                 }
+                STACKADJ(-oparg);
                 if (err != 0) {
                     Py_DECREF(x);
                     break;