Fix up dis to understand oparg of END_ASYNC_FOR

Author: markshannon

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') # No 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_dis.py

@@ -1256,15 +1256,21 @@ def test__try_compile_no_context_exc_on_error(self):
         except Exception as e:
             self.assertIsNone(e.__context__)
 
-    def test_async_for(self):
+    def test_async_for_presentation(self):
 
         async def afunc():
             async for letter in async_iter1:
                 l2
             l3
 
-        expected = ""
-        self.do_disassembly_test(afunc, expected)
+        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