[Checkins] [zopefoundation/persistent] e8b9c8: Avoid raising a SystemError when clearing slots if...

[GitHub]

  Branch: refs/heads/jam-systemerror
  Home:   https://github.com/zopefoundation/persistent
  Commit: e8b9c8e9d886e8908f31dc7aa26333311ff8b614
      https://github.com/zopefoundation/persistent/commit/e8b9c8e9d886e8908f31dc7aa26333311ff8b614
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2017-03-20 (Mon, 20 Mar 2017)

  Changed paths:
    M CHANGES.rst
    M persistent/cPersistence.c
    M persistent/tests/test_persistence.py

  Log Message:
  -----------
  Avoid raising a SystemError when clearing slots if setstate() failed.

PR #52 introduced a code path to `ghostify` that calls PyErr_Clear()
with the intent to avoid propagating AttributeErrors for slots.

However, if there is an error (like a POSKeyError) raised by
jar.setstate(), then `unghostify` will call ghostify with an error
pending. If the object had slots that weren't set and the
AttributeError was cleared, so was the pending error from setstate. So
when `ghostify` returned NULL that got propagated up to the
interpreter which finds no exception and so raises `SystemError: error
return without exception set`.

This commit makes `unghostify` save and restore the exception state
around the call to PyErr_Clear.