Use case body location for POP_TOP after case test, to give better locations for BRANCH events.

Author: markshannon

Lib/test/test_monitoring.py

@@ -1681,6 +1681,37 @@ async def foo():
             ('branch left', 'func', 12, 12)])
 
 
+    def test_async_for(self):
+
+        def func(v=1):
+            x = 0
+            for v in range(4):
+                match v:
+                    case 1:
+                        x += 1
+                    case 2:
+                        x += 2
+                    case 3:
+                        x += 3
+            return x
+
+        self.check_events(func, recorders = BRANCHES_RECORDERS, expected = [
+            ('branch left', 'func', 2, 2),
+            ('branch right', 'func', 4, 6),
+            ('branch right', 'func', 6, 8),
+            ('branch left', 'func', 8, 8),
+            ('branch left', 'func', 2, 2),
+            ('branch left', 'func', 4, 5),
+            ('branch left', 'func', 2, 2),
+            ('branch right', 'func', 4, 6),
+            ('branch left', 'func', 6, 7),
+            ('branch left', 'func', 2, 2),
+            ('branch right', 'func', 4, 6),
+            ('branch right', 'func', 6, 8),
+            ('branch right', 'func', 8, 9),
+            ('branch right', 'func', 2, 10)])
+
+
 class TestBranchConsistency(MonitoringTestBase, unittest.TestCase):
 
     def check_branches(self, func, tool=TEST_TOOL, recorders=BRANCH_OFFSET_RECORDERS):

Python/codegen.c

@@ -6121,7 +6121,9 @@ codegen_match_inner(compiler *c, stmt_ty s, pattern_context *pc)
         }
         // Success! Pop the subject off, we're done with it:
         if (i != cases - has_default - 1) {
-            ADDOP(c, LOC(m->pattern), POP_TOP);
+            /* Use the body location to give better locations for branch events */
+            assert(asdl_seq_LEN(m->body) > 0);
+            ADDOP(c, LOC(asdl_seq_GET(m->body, 0)), POP_TOP);
         }
         VISIT_SEQ(c, stmt, m->body);
         ADDOP_JUMP(c, NO_LOCATION, JUMP, end);