Issue 33509: warnings.warn_explicit with module_globals=True raises a SystemError

Reproducible with:

import warnings
warnings.warn_explicit("msg", DeprecationWarning, "name", 1, module_globals=None)

It may be related to:

commit d4f8480dfe89447587550a85b61d4e9faf827e98
Author: Serhiy Storchaka <storchaka@gmail.com>
Date:   Sat Nov 11 15:19:47 2017 +0200

    bpo-31572: Don't silence unexpected errors in the _warnings module. (#3731)
    
    Get rid of _PyObject_HasAttrId() and PyDict_GetItemString().
    Silence only expected AttributeError, KeyError and ImportError when
    get an attribute, look up in a dict or import a module.

I choose the release blocker priority, since IMHO it's an easy fix.

This bug was before commit d4f8480dfe89447587550a85b61d4e9faf827e98.

New changeset b056562860c227bad2e0ba7cd3130e115c007768 by Victor Stinner in branch 'master':
bpo-33509: Fix _warnings for module_globals=None (#6833)
https://github.com/python/cpython/commit/b056562860c227bad2e0ba7cd3130e115c007768

New changeset 820219f7867f2bbfe0ac4d4f0d1ea1fdef7795a9 by Miss Islington (bot) in branch '3.7':
bpo-33509: Fix _warnings for module_globals=None (GH-6833)
https://github.com/python/cpython/commit/820219f7867f2bbfe0ac4d4f0d1ea1fdef7795a9

Thanks for the report and thanks for the fix!

This test is failed with -We.

$ ./python -We -m test -v test_warnings
...
======================================================================
ERROR: test_module_globals (test.test_warnings.CFilterTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_warnings/__init__.py", line 226, in test_module_globals
    module_globals=None)
UserWarning: msg

======================================================================
ERROR: test_module_globals (test.test_warnings.PyFilterTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_warnings/__init__.py", line 226, in test_module_globals
    module_globals=None)
  File "/home/serhiy/py/cpython/Lib/warnings.py", line 375, in warn_explicit
    raise message
UserWarning: msg

----------------------------------------------------------------------

New changeset e292b75e3ecdc6bbe81cda09de836dc9e27ab9e6 by Ned Deily (Victor Stinner) in branch 'master':
bpo-33509: Fix test_warnings for python3 -Werror (GH-7365)
https://github.com/python/cpython/commit/e292b75e3ecdc6bbe81cda09de836dc9e27ab9e6

New changeset d2c6ecc234e705b60cbcbb9dd4c99022407d0dd0 by Miss Islington (bot) in branch '3.7':
bpo-33509: Fix test_warnings for python3 -Werror (GH-7365)
https://github.com/python/cpython/commit/d2c6ecc234e705b60cbcbb9dd4c99022407d0dd0

> This test is failed with -We.

Thank you Serhiy for the bug report. It should now be fixed again.

messages: + msg318700
stage: patch review -> resolved

messages: + msg318564

resolution: fixed
stage: patch review -> resolved