Compiler warning when using C23: initialization discards 'const' qualifier from pointer target type

[heitbaum]

Bug report

Bug description:

../Python/preconfig.c: In function '_Py_get_xoption':
../Python/preconfig.c:587:24: warning: initialization discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
  587 |         wchar_t *sep = wcschr(option, L'=');
      |                        ^~~~~~
../Python/preconfig.c: In function 'preconfig_init_utf8_mode':
../Python/preconfig.c:618:24: warning: initialization discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
{
  618 |         wchar_t *sep = wcschr(xopt, L'=');
      |                        ^~~~~~

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-145092: fix discards const qualifier from pointer #145093
• gh-145092: fix discards const qualifier from pointer #145095
• [3.13] gh-145092: Fix compiler warning for memchr() and wcschr() returning const pointer (GH-145093) #145101
• [3.14] gh-145092: Fix compiler warning for memchr() and wcschr() returning const pointer (GH-145093) #145102

[brianschubert]

Are you using a C++ compiler? wcschr returns a const pointer in C++ (ref) and a non-const in C (ref). Python/preconfig.c is a C file and should be compiled as C, not C++.

[heitbaum]

Issue is since glibc-2.43 along side gcc-15/16

Since glibc-2.43 and ISO C23, the functions bsearch, memchr, strchr, strpbrk, strrchr, strstr, wcschr, wcspbrk, wcsrchr, wcsstr and wmemchr that return pointers into their input arrays now have definitions as macros that return a pointer to a const-qualified type when the input argument is a pointer to a const-qualified type.

char * pointer returns are only being used for comparisons so declare then as const, which matches the input variables.