Warnings from {fmt} when using xchar.h header and -fsigned-char flag on ARM

[alexezeder]

On the latest {fmt} version (8.0, master) I get these warnings just by including {fmt} headers (https://godbolt.org/z/arEYeq9rx):

/fmt/trunk/include/fmt/format.h:1026:17: warning: comparison of integer expressions of different signedness: 'const wchar_t' and 'const char' [-Wsign-compare]
 1026 |   return lhs[0] == rhs[0] && lhs[1] == rhs[1];
      |          ~~~~~~~^~~~~~~~~
...
/fmt/trunk/include/fmt/core.h:2092:14: warning: comparison of integer expressions of different signedness: 'const wchar_t' and 'char' [-Wsign-compare]
 2092 |     if (*out == value) return true;
      |         ~~~~~^~~~~~~~

from here:

fmt/include/fmt/format.h

Lines 1025 to 1027 in c3c27e5

	template <typename Char> auto equal2(const Char* lhs, const char* rhs) -> bool {
	return lhs[0] == rhs[0] && lhs[1] == rhs[1];
	}

fmt/include/fmt/core.h

Lines 2088 to 2095 in c3c27e5

	// Return the result via the out param to workaround gcc bug 77539.
	template <bool IS_CONSTEXPR, typename T, typename Ptr = const T*>
	FMT_CONSTEXPR auto find(Ptr first, Ptr last, T value, Ptr& out) -> bool {
	for (out = first; out != last; ++out) {
	if (*out == value) return true;
	}
	return false;
	}

These warnings are pretty logical since the signedness of char-types (char and wchar_t) is different in this case - https://godbolt.org/z/1Pdxbesvf.

Still, there are no warnings with {fmt} 7.1.3 - https://godbolt.org/z/T1qPjfoaG.

I'm not familiar with that part of the library, so maybe someone can find the cause of this regression in few seconds, for example, @vitaut 😉

[vitaut]

It's unclear why there were no warnings in 7.1.3 but I fixed them in 785908e. Thanks for reporting.

[alexezeder]

Thank you for fixing this!