signed/unsigned mismatch in Py_UNICODE_ISSPACE macro

[doko42]

BPO	43030
Nosy	@doko42, @vstinner, @methane, @serhiy-storchaka, @miss-islington
PRs	bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE with signed wchar_t #24350 [3.9] bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE with signed wchar_t (GH-24350) #24396 [3.8] bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE with signed wchar_t (GH-24350) #24397

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

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GitHub fields:

assignee = None
closed_at = <Date 2021-01-31.14:46:58.135>
created_at = <Date 2021-01-26.12:40:22.465>
labels = ['expert-C-API', '3.8', '3.9', '3.10']
title = 'signed/unsigned mismatch in Py_UNICODE_ISSPACE macro'
updated_at = <Date 2021-01-31.14:46:58.131>
user = 'https://github.com/doko42'

bugs.python.org fields:

activity = <Date 2021-01-31.14:46:58.131>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2021-01-31.14:46:58.135>
closer = 'serhiy.storchaka'
components = ['C API']
creation = <Date 2021-01-26.12:40:22.465>
creator = 'doko'
dependencies = []
files = []
hgrepos = []
issue_num = 43030
keywords = ['patch']
message_count = 8.0
messages = ['385707', '385708', '385711', '385747', '385750', '386016', '386019', '386022']
nosy_count = 5.0
nosy_names = ['doko', 'vstinner', 'methane', 'serhiy.storchaka', 'miss-islington']
pr_nums = ['24350', '24396', '24397']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue43030'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[doko42]

[forwarded from https://bugs.debian.org/961396]

$ cat > foo.c
#include <Python.h>

int main(int argc, char *argv[])
{
        Py_UNICODE x = 0;

        return Py_UNICODE_ISSPACE(x);
}

$ gcc -Wsign-compare -Werror $(pkg-config --cflags python3) foo.c
In file included from /usr/include/python3.9/unicodeobject.h:1026,
                 from /usr/include/python3.9/Python.h:97,
                 from foo.c:1:
foo.c: In function ‘main’:
/usr/include/python3.9/cpython/unicodeobject.h:25:11: error: comparison of integer expressions of different signedness: ‘Py_UNICODE’ {aka ‘int’} and ‘unsigned int’ [-Werror=sign-compare]
   25 |     ((ch) < 128U ? _Py_ascii_whitespace[(ch)] : _PyUnicode_IsWhitespace(ch))
      |           ^
foo.c:7:16: note: in expansion of macro ‘Py_UNICODE_ISSPACE’
    7 |         return Py_UNICODE_ISSPACE(x);
      |                ^~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

[vstinner]

‘Py_UNICODE’ {aka ‘int’}

Python defines Py_UNICODE as wchar_t: typedef wchar_t Py_UNICODE;

Is wchar_t signed (int type) on Debian? Which is your architecture?

[forwarded from https://bugs.debian.org/961396]

It says amd64.

[doko42]

# 26 "/usr/include/stdlib.h" 2 3 4
# 1 "/usr/lib/gcc/x86_64-linux-gnu/10/include/stddef.h" 1 3 4
# 321 "/usr/lib/gcc/x86_64-linux-gnu/10/include/stddef.h" 3 4
typedef int wchar_t;
# 32 "/usr/include/stdlib.h" 2 3 4

[...]

# 1 "/usr/include/python3.9/cpython/unicodeobject.h" 1
# 14 "/usr/include/python3.9/cpython/unicodeobject.h"
typedef wchar_t Py_UNICODE;
# 53 "/usr/include/python3.9/cpython/unicodeobject.h"

yes, x86_64-linux-gnu.

[methane]

Just replacing "128U" with "128" enough?
Will ch < 128 emit warning on platforms wchar_t is unsigned?

[serhiy-storchaka]

No, it is not enough, because we do not want to use ch as index if it is negative.

[serhiy-storchaka]

New changeset 42b1806 by Serhiy Storchaka in branch 'master':
bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE with signed wchar_t (GH-24350)
42b1806

[miss-islington]

New changeset 995a6c0 by Miss Islington (bot) in branch '3.9':
bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE with signed wchar_t (GH-24350)
995a6c0

[serhiy-storchaka]

New changeset 229ef39 by Miss Islington (bot) in branch '3.8':
bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE with signed wchar_t (GH-24350) (GH-24397)
229ef39