Crash when setting attribute with string subclass as the name (--with-pydebug)

[ronaldoussoren]

BPO	46903
Nosy	@ronaldoussoren, @methane, @markshannon, @tirkarthi, @sweeneyde
PRs	bpo-46903: Handle str-subclasses in virtual instance dictionaries. #31658 bpo-46903: Use assertEqual, not assertEquals in test_unicode #31718

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2022-03-06.20:19:52.404>
created_at = <Date 2022-03-02.21:30:36.583>
labels = ['interpreter-core', 'type-crash', '3.11']
title = 'Crash when setting attribute with string subclass as the name (--with-pydebug)'
updated_at = <Date 2022-03-07.07:06:38.693>
user = 'https://github.com/ronaldoussoren'

bugs.python.org fields:

activity = <Date 2022-03-07.07:06:38.693>
actor = 'Dennis Sweeney'
assignee = 'none'
closed = True
closed_date = <Date 2022-03-06.20:19:52.404>
closer = 'ronaldoussoren'
components = ['Interpreter Core']
creation = <Date 2022-03-02.21:30:36.583>
creator = 'ronaldoussoren'
dependencies = []
files = []
hgrepos = []
issue_num = 46903
keywords = ['patch']
message_count = 7.0
messages = ['414386', '414387', '414400', '414515', '414616', '414624', '414640']
nosy_count = 5.0
nosy_names = ['ronaldoussoren', 'methane', 'Mark.Shannon', 'xtreak', 'Dennis Sweeney']
pr_nums = ['31658', '31718']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue46903'
versions = ['Python 3.11']

[ronaldoussoren]

The script below fails with an assertion error with python 3.11a5+ (current trunk) when build with --with-pydebug:

# BEGIN OF FILE
class String(str):
    __slots__ = ()

name = String("hello")

class Bag:
    pass

o = Bag()
setattr(o, name, 42)

# END OF FILE

Error output:

% /tmp/py311/bin/python3 -Xdev str.py (master)pyobjc-8
Assertion failed: (PyUnicode_CheckExact(name)), function _PyObject_StoreInstanceAttribute, file dictobject.c, line 5426.
Fatal Python error: Aborted

Current thread 0x0000000100a98580 (most recent call first):
File "/Users/ronald/Projects/pyobjc-8/pyobjc-core/str.py", line 10 in <module>
zsh: abort /tmp/py311/bin/python3 -Xdev str.py

[ronaldoussoren]

A hard crash seems wrong to me, and I'm not convinced yet that checking that the type of the attribute name is exactly string is correct.

Found while debugging a crash in PyObjC's testsuite, PyObjC uses a subclass of str to represent Objective-C strings. Using such instances works fine in practice, but causes a crash in a --with-pydebug build due to this assertion.

[sweeneyde]

a8b9350 is the first bad commit
commit a8b9350
Author: Mark Shannon <mark@hotpy.org>
Date: Wed Oct 13 14:19:34 2021 +0100

bpo-45340: Don't create object dictionaries unless actually needed (GH-28802)

* Never change types' cached keys. It could invalidate inline attribute objects.

* Lazily create object dictionaries.

* Update specialization of LOAD/STORE_ATTR.

* Don't update shared keys version for deletion of value.

* Update gdb support to handle instance values.

* Rename SPLIT_KEYS opcodes to INSTANCE_VALUE.

[markshannon]

New changeset 03c2a36 by Mark Shannon in branch 'main':
bpo-46903: Handle str-subclasses in virtual instance dictionaries. (GH-31658)
03c2a36

[markshannon]

Ronald, does PR 31658 fix your issue?

[ronaldoussoren]

Your PR fixed the issue for me.

[tirkarthi]

The PR introduced some deprecation warnings in tests.

./python -Wall -m test test_unicode
0:00:00 load avg: 1.54 Run tests sequentially
0:00:00 load avg: 1.54 [1/1] test_unicode
/home/karthikeyan/stuff/python/cpython/Lib/test/test_unicode.py:3058: DeprecationWarning: Please use assertEqual instead.
self.assertEquals(o.name, 1)
/home/karthikeyan/stuff/python/cpython/Lib/test/test_unicode.py:3060: DeprecationWarning: Please use assertEqual instead.
self.assertEquals(list(o.__dict__), [name])
/home/karthikeyan/stuff/python/cpython/Lib/test/test_unicode.py:3067: DeprecationWarning: Please use assertEqual instead.
self.assertEquals(o.name2, 3)
/home/karthikeyan/stuff/python/cpython/Lib/test/test_unicode.py:3069: DeprecationWarning: Please use assertEqual instead.
self.assertEquals(list(o.__dict__), [name, name2])

== Tests result: SUCCESS ==

1 test OK.

Total duration: 952 ms
Tests result: SUCCESS