bpo-46161: fix the bug of starunpack_helper in compile.c

[zq1997]

pushed should also be considered when building tuples. Otherwise, when the remaining arguments are constant, it will ignore the pushed ones.

Consider this code,

class MyMetaclass(type): pass
use_metaclass = {'metaclass': MyMetaclass}
class MyClass(1, 2, 3, **use_metaclass): pass

and its bytecode,

  1           0 LOAD_BUILD_CLASS
              2 LOAD_CONST               0 (<code object MyMetaclass at 0x7f4dfea6db40, file "bug.py", line 1>)
              4 MAKE_FUNCTION            0
              6 LOAD_CONST               1 ('MyMetaclass')
              8 LOAD_NAME                0 (type)
             10 CALL_NO_KW               3
             12 STORE_NAME               1 (MyMetaclass)

  2          14 LOAD_CONST               2 ('metaclass')
             16 LOAD_NAME                1 (MyMetaclass)
             18 BUILD_MAP                1
             20 STORE_NAME               2 (use_metaclass)

  3          22 LOAD_BUILD_CLASS
             24 LOAD_CONST               3 (<code object MyClass at 0x7f4dfea6d540, file "bug.py", line 3>)
             26 MAKE_FUNCTION            0
             28 LOAD_CONST               4 ('MyClass')
             30 LOAD_CONST               5 ((1, 2, 3))
             32 BUILD_MAP                0
             34 LOAD_NAME                2 (use_metaclass)
             36 DICT_MERGE               1
             38 CALL_FUNCTION_EX         1
             40 STORE_NAME               3 (MyClass)
             42 LOAD_CONST               6 (None)
             44 RETURN_VALUE

Obviously, the arguments were incorrectly constructed, and the string MyClass was called instead of the class builder.

Traceback (most recent call last):
  File "xxxx/bug.py", line 3, in <module>
    class MyClass(1, 2, 3, **use_metaclass): pass
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'str' object is not callable

The more serious problem is that it makes the stack unbalanced.

https://bugs.python.org/issue46161

[the-knights-who-say-ni]

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[sweeneyde]

Hi @zq1997, thanks for the report and the patch! It would be nice if you could add some sort of regression test.

Also, as the bot said, make sure to get your CLA signed, and this should get a NEWS entry as well. Thanks!

[zq1997]

I have added the test code and NEWS entry. The CLA seems to take a while to take effect.

[sweeneyde]

@markshannon Can this be merged now?