gh-93061: Mark as artificial: backwards jump after async for (GH-93120)

Author: sweeneyde

Lib/test/test_sys_settrace.py

@@ -607,6 +607,58 @@ def run(tracer):
         self.compare_events(doit_async.__code__.co_firstlineno,
                             tracer.events, events)
 
+    def test_async_for_backwards_jump_has_no_line(self):
+        async def arange(n):
+            for i in range(n):
+                yield i
+        async def f():
+            async for i in arange(3):
+                if i > 100:
+                    break # should never be traced
+
+        tracer = self.make_tracer()
+        coro = f()
+        try:
+            sys.settrace(tracer.trace)
+            coro.send(None)
+        except Exception:
+            pass
+        finally:
+            sys.settrace(None)
+
+        events = [
+            (0, 'call'),
+            (1, 'line'),
+            (-3, 'call'),
+            (-2, 'line'),
+            (-1, 'line'),
+            (-1, 'return'),
+            (1, 'exception'),
+            (2, 'line'),
+            (1, 'line'),
+            (-1, 'call'),
+            (-2, 'line'),
+            (-1, 'line'),
+            (-1, 'return'),
+            (1, 'exception'),
+            (2, 'line'),
+            (1, 'line'),
+            (-1, 'call'),
+            (-2, 'line'),
+            (-1, 'line'),
+            (-1, 'return'),
+            (1, 'exception'),
+            (2, 'line'),
+            (1, 'line'),
+            (-1, 'call'),
+            (-2, 'line'),
+            (-2, 'return'),
+            (1, 'exception'),
+            (1, 'return'),
+        ]
+        self.compare_events(f.__code__.co_firstlineno,
+                            tracer.events, events)
+
     def test_21_repeated_pass(self):
         def func():
             pass

Misc/NEWS.d/next/Core and Builtins/2022-05-22-02-37-50.gh-issue-93061.r70Imp.rst

@@ -0,0 +1 @@
+Backward jumps after ``async for`` loops are no longer given dubious line numbers.

Python/compile.c

@@ -2925,6 +2925,8 @@ compiler_async_for(struct compiler *c, stmt_ty s)
     /* Success block for __anext__ */
     VISIT(c, expr, s->v.AsyncFor.target);
     VISIT_SEQ(c, stmt, s->v.AsyncFor.body);
+    /* Mark jump as artificial */
+    c->u->u_lineno = -1;
     ADDOP_JUMP(c, JUMP_ABSOLUTE, start);
 
     compiler_pop_fblock(c, FOR_LOOP, start);