sign-conversion warning in 3.9 beta

[henryiii]

BPO	41366
Nosy	@methane, @henryiii, @miss-islington
PRs	bpo-41366: Fix clang warning for sign conversion #21592 [3.9] bpo-41366: Fix clang warning for sign conversion (GH-21592) #21600

^{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 2020-07-23.09:01:18.290>
created_at = <Date 2020-07-22.03:49:41.130>
labels = ['expert-C-API', 'build', '3.9', '3.10']
title = 'sign-conversion warning in 3.9 beta'
updated_at = <Date 2020-07-23.09:01:18.289>
user = 'https://github.com/henryiii'

bugs.python.org fields:

activity = <Date 2020-07-23.09:01:18.289>
actor = 'methane'
assignee = 'none'
closed = True
closed_date = <Date 2020-07-23.09:01:18.290>
closer = 'methane'
components = ['C API']
creation = <Date 2020-07-22.03:49:41.130>
creator = 'Henry Schreiner'
dependencies = []
files = []
hgrepos = []
issue_num = 41366
keywords = ['patch']
message_count = 4.0
messages = ['374084', '374130', '374131', '374132']
nosy_count = 4.0
nosy_names = ['methane', 'python-dev', 'Henry Schreiner', 'miss-islington']
pr_nums = ['21592', '21600']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue41366'
versions = ['Python 3.9', 'Python 3.10']

[henryiii]

The macro Py_UNICODE_COPY was replaced by a function in CPython 3.9, and that function cannot compile with full warnings enabled + warnings as errors under Clang. The problematic line:

Py_DEPRECATED(3.3) static inline void
Py_UNICODE_COPY(Py_UNICODE *target, const Py_UNICODE *source, Py_ssize_t length) {
memcpy(target, source, length * sizeof(Py_UNICODE));
}

has an implicit conversion of Py_ssize_t into size_t, which creates:

/Users/runner/hostedtoolcache/Python/3.9.0-beta.5/x64/include/python3.9/cpython/unicodeobject.h:55:: implicit conversion changes signedness: 'Py_ssize_t' (aka 'long') to 'unsigned long' [-Werror,-Wsign-conversion]

error: implicit conversion changes signedness: 'Py_ssize_t' (aka 'long') to 'unsigned long' [-Werror,-Wsign-conversion]
memcpy(target, source, length * sizeof(Py_UNICODE)); memcpy(target, source, length * sizeof(Py_UNICODE));

An explicit cast to size_t (is there a Py_size_t?) should be made.

[methane]

New changeset 680254a by Henry Schreiner in branch 'master':
bpo-41366: Fix clang warning for sign conversion (GH-21592)
680254a

[miss-islington]

New changeset e8dda90 by Miss Islington (bot) in branch '3.9':
bpo-41366: Fix clang warning for sign conversion (GH-21592)
e8dda90

[methane]

Thank you.