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Replace the locale #if in chrono.h with a shim template

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Both specializations are always parsed while only the selected one is
instantiated. The #else branch it replaces is compiled by no target:
nolocale-test builds src/format.cc, which never reaches chrono.h.
This commit is contained in:
Victor Zverovich 2026-09-18 12:23:34 -07:00
parent e4751cc709
commit b9a6f9be76
1 changed files with 38 additions and 40 deletions
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78
include/fmt/chrono.h
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@ -407,47 +407,46 @@ auto write(OutputIt out, const std::tm& time, const std::locale& loc,
return write_encoded_tm_str(out, string_view(buf.data(), buf.size()), loc);
}
#if FMT_USE_LOCALE
// The locale used for localized formatting: the one passed to the formatting
// function or the global locale if none was passed.
inline auto get_locale(locale_ref loc, bool localized) -> std::locale {
if (!localized) return get_classic_locale();
return loc.get<std::locale>();
}
// locale_ref::get<std::locale>() is ill-formed when FMT_USE_LOCALE is 0, so
// that branch must not be instantiated.
template <bool UseLocale = FMT_USE_LOCALE != 0> struct locale_writer {
static auto is_classic(locale_ref loc) -> bool {
return loc.get<std::locale>() == get_classic_locale();
}
inline auto is_classic_locale(locale_ref loc, bool localized) -> bool {
return !localized || loc.get<std::locale>() == get_classic_locale();
}
// Only called when the locale is localized and not classic.
template <typename Char, typename OutputIt>
static auto write_time(OutputIt out, const std::tm& time, locale_ref loc,
char format, char modifier) -> OutputIt {
return write<Char>(out, time, loc.get<std::locale>(), format, modifier);
}
template <typename Char, typename OutputIt>
auto write_localized_time(OutputIt out, const std::tm& time, locale_ref loc,
bool localized, char format, char modifier)
-> OutputIt {
return write<Char>(out, time, get_locale(loc, localized), format, modifier);
}
// An empty locale_ref means the global locale, not the classic one.
template <typename Char, typename OutputIt>
static auto write_str(OutputIt out, string_view sv, locale_ref loc,
bool localized) -> OutputIt {
if (!localized) return write_tm_str<Char>(out, sv, get_classic_locale());
return write_tm_str<Char>(out, sv, loc.get<std::locale>());
}
};
template <typename Char, typename OutputIt>
auto write_localized_str(OutputIt out, string_view sv, locale_ref loc,
bool localized) -> OutputIt {
return write_tm_str<Char>(out, sv, get_locale(loc, localized));
}
#else
constexpr auto is_classic_locale(locale_ref, bool) -> bool { return true; }
template <> struct locale_writer<false> {
static constexpr auto is_classic(locale_ref) -> bool { return true; }
// Never called because is_classic_locale() is always true.
template <typename Char, typename OutputIt>
auto write_localized_time(OutputIt out, const std::tm&, locale_ref, bool, char,
char) -> OutputIt {
return out;
}
// Never called because is_classic() is always true.
template <typename Char, typename OutputIt>
static auto write_time(OutputIt out, const std::tm&, locale_ref, char, char)
-> OutputIt {
return out;
}
// Zone names are ASCII, so there is nothing to transcode.
template <typename Char, typename OutputIt>
auto write_localized_str(OutputIt out, string_view sv, locale_ref, bool)
-> OutputIt {
return copy<Char>(sv.data(), sv.data() + sv.size(), out);
}
#endif // FMT_USE_LOCALE
// Zone names are ASCII, so there is nothing to transcode.
template <typename Char, typename OutputIt>
static auto write_str(OutputIt out, string_view sv, locale_ref, bool)
-> OutputIt {
return copy<Char>(sv.data(), sv.data() + sv.size(), out);
}
};
template <typename T, typename U>
using is_similar_arithmetic_type =
@ -1235,7 +1234,7 @@ class tm_writer {
template <typename T, FMT_ENABLE_IF(has_tm_zone<T>::value)>
void format_tz_name(const T& tm) {
if (!tm.tm_zone) FMT_THROW(format_error("no timezone"));
out_ = write_localized_str<Char>(out_, tm.tm_zone, loc_, localized_);
out_ = locale_writer<>::write_str<Char>(out_, tm.tm_zone, loc_, localized_);
}
template <typename T, FMT_ENABLE_IF(!has_tm_zone<T>::value)>
void format_tz_name(const T&) {
@ -1243,8 +1242,7 @@ class tm_writer {
}
void format_localized(char format, char modifier = 0) {
out_ = write_localized_time<Char>(out_, tm_, loc_, localized_, format,
modifier);
out_ = locale_writer<>::write_time<Char>(out_, tm_, loc_, format, modifier);
}
public:
@ -1252,7 +1250,7 @@ class tm_writer {
const Duration* subsecs = nullptr)
: loc_(loc),
localized_(localized),
is_classic_(is_classic_locale(loc, localized)),
is_classic_(!localized || locale_writer<>::is_classic(loc)),
out_(out),
subsecs_(subsecs),
tm_(tm) {}