GH-128534: Fix behavior of branch monitoring for async for

Include/internal/pycore_magic_number.h

@@ -270,6 +270,7 @@ Known values:
     Python 3.14a5 3615 (CALL_FUNCTION_EX always take a kwargs argument)
     Python 3.14a5 3616 (Remove BINARY_SUBSCR and family. Make them BINARY_OPs)
     Python 3.14a6 3617 (Branch monitoring for async for loops)
+    Python 3.14a6 3618 (Add oparg to END_ASYNC_FOR)
 
     Python 3.15 will start with 3650
 
@@ -282,7 +283,7 @@ PC/launcher.c must also be updated.
 
 */
 
-#define PYC_MAGIC_NUMBER 3617
+#define PYC_MAGIC_NUMBER 3618
 /* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
    (little-endian) and then appending b'\r\n'. */
 #define PYC_MAGIC_NUMBER_TOKEN \

Lib/dis.py

@@ -52,6 +52,7 @@
 STORE_FAST_STORE_FAST = opmap['STORE_FAST_STORE_FAST']
 IS_OP = opmap['IS_OP']
 CONTAINS_OP = opmap['CONTAINS_OP']
+END_ASYNC_FOR = opmap['END_ASYNC_FOR']
 
 CACHE = opmap["CACHE"]
 
@@ -605,7 +606,8 @@ def get_argval_argrepr(self, op, arg, offset):
                 argval = self.offset_from_jump_arg(op, arg, offset)
                 lbl = self.get_label_for_offset(argval)
                 assert lbl is not None
-                argrepr = f"to L{lbl}"
+                preposition = "from" if deop == END_ASYNC_FOR else "to"
+                argrepr = f"{preposition} L{lbl}"
             elif deop in (LOAD_FAST_LOAD_FAST, STORE_FAST_LOAD_FAST, STORE_FAST_STORE_FAST):
                 arg1 = arg >> 4
                 arg2 = arg & 15
@@ -745,7 +747,8 @@ def _parse_exception_table(code):
 
 def _is_backward_jump(op):
     return opname[op] in ('JUMP_BACKWARD',
-                          'JUMP_BACKWARD_NO_INTERRUPT')
+                          'JUMP_BACKWARD_NO_INTERRUPT',
+                          'END_ASYNC_FOR') # Not really a jump, but it has a "target"
 
 def _get_instructions_bytes(code, linestarts=None, line_offset=0, co_positions=None,
                             original_code=None, arg_resolver=None):

Lib/test/test_code.py

@@ -936,6 +936,15 @@ def with_extended_args(x):
             get_line_branches(with_extended_args),
             [(1,2,8)])
 
+        async def afunc():
+            async for letter in async_iter1:
+                2
+            3
+
+        self.assertEqual(
+            get_line_branches(afunc),
+            [(1,1,3)])
+
 if check_impl_detail(cpython=True) and ctypes is not None:
     py = ctypes.pythonapi
     freefunc = ctypes.CFUNCTYPE(None,ctypes.c_voidp)

Lib/test/test_dis.py

@@ -1256,6 +1256,23 @@ def test__try_compile_no_context_exc_on_error(self):
         except Exception as e:
             self.assertIsNone(e.__context__)
 
+    def test_async_for_presentation(self):
+
+        async def afunc():
+            async for letter in async_iter1:
+                l2
+            l3
+
+        disassembly =  self.get_disassembly(afunc)
+        for line in disassembly.split("\n"):
+            if "END_ASYNC_FOR" in line:
+                break
+        else:
+            self.fail("No END_ASYNC_FOR in disassembly of async for")
+        self.assertNotIn("to", line)
+        self.assertIn("from", line)
+
+
     @staticmethod
     def code_quicken(f):
         _testinternalcapi = import_helper.import_module("_testinternalcapi")