[libc++] Remove the need for uselocale() (llvm#120158)

Instead of requiring `uselocale()` as part of the base locale API,
define __locale_guard in the few places that need it directly, without
making __locale_guard part of the base API.

In practice, most mainstream platforms never used __locale_guard, so
they also didn't need to define uselocale(), and after this patch they
actually don't define it anymore.

Author: ldionne

libcxx/include/CMakeLists.txt

@@ -503,7 +503,6 @@ set(files
   __locale_dir/locale_base_api/ibm.h
   __locale_dir/locale_base_api/musl.h
   __locale_dir/locale_base_api/openbsd.h
-  __locale_dir/locale_guard.h
   __locale_dir/pad_and_output.h
   __locale_dir/support/apple.h
   __locale_dir/support/bsd_like.h

libcxx/include/__locale_dir/locale_base_api.h

@@ -23,14 +23,12 @@
 // Variadic functions may be implemented as templates with a parameter pack instead
 // of C-style variadic functions.
 //
-// TODO: I think __uselocale() is not necessary if we refactor a bit.
 // TODO: __localeconv shouldn't take a reference, but the Windows implementation doesn't allow copying __locale_t
 //
 // Locale management
 // -----------------
 // namespace __locale {
 //  using __locale_t = implementation-defined;
-//  __locale_t  __uselocale(__locale_t);
 //  __locale_t  __newlocale(int, const char*, __locale_t);
 //  void        __freelocale(__locale_t);
 //  lconv*      __localeconv(__locale_t&);
@@ -139,10 +137,6 @@ namespace __locale {
 //
 using __locale_t = locale_t;
 
-#  ifndef _LIBCPP_MSVCRT_LIKE
-inline _LIBCPP_HIDE_FROM_ABI __locale_t __uselocale(__locale_t __loc) { return uselocale(__loc); }
-#  endif
-
 inline _LIBCPP_HIDE_FROM_ABI __locale_t __newlocale(int __category_mask, const char* __name, __locale_t __loc) {
   return newlocale(__category_mask, __name, __loc);
 }

libcxx/include/__locale_dir/locale_base_api/bsd_locale_fallbacks.h

@@ -14,8 +14,6 @@
 #define _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_BSD_LOCALE_FALLBACKS_H
 
 #include <locale.h>
-
-#include <__locale_dir/locale_guard.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -30,6 +28,20 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+struct __locale_guard {
+  _LIBCPP_HIDE_FROM_ABI __locale_guard(locale_t& __loc) : __old_loc_(::uselocale(__loc)) {}
+
+  _LIBCPP_HIDE_FROM_ABI ~__locale_guard() {
+    if (__old_loc_)
+      ::uselocale(__old_loc_);
+  }
+
+  locale_t __old_loc_;
+
+  __locale_guard(__locale_guard const&)            = delete;
+  __locale_guard& operator=(__locale_guard const&) = delete;
+};
+
 inline _LIBCPP_HIDE_FROM_ABI decltype(MB_CUR_MAX) __libcpp_mb_cur_max_l(locale_t __l) {
   __locale_guard __current(__l);
   return MB_CUR_MAX;

libcxx/include/__locale_dir/locale_guard.h

@@ -38,8 +38,6 @@ namespace __locale {
 //
 using __locale_t = ::locale_t;
 
-inline _LIBCPP_HIDE_FROM_ABI __locale_t __uselocale(__locale_t __loc) { return ::uselocale(__loc); }
-
 inline _LIBCPP_HIDE_FROM_ABI __locale_t __newlocale(int __category_mask, const char* __locale, __locale_t __base) {
   return ::newlocale(__category_mask, __locale, __base);
 }

libcxx/include/__locale_dir/support/bsd_like.h

@@ -149,10 +149,6 @@ class __locale_t {
   __lconv_storage* __lc_ = nullptr;
 };
 
-// __uselocale can't be implemented on Windows because Windows allows partial modification
-// of thread-local locale and so _get_current_locale() returns a copy while __uselocale does
-// not create any copies. We can still implement RAII even without __uselocale though.
-__locale_t __uselocale(__locale_t) = delete;
 _LIBCPP_EXPORTED_FROM_ABI __locale_t __newlocale(int __mask, const char* __locale, __locale_t __base);
 inline _LIBCPP_HIDE_FROM_ABI void __freelocale(__locale_t __loc) { ::_free_locale(__loc); }
 _LIBCPP_EXPORTED_FROM_ABI lconv* __localeconv(__locale_t& __loc);
@@ -288,6 +284,44 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(__scanf__, 3, 4) int __s
 _LIBCPP_DIAGNOSTIC_POP
 #undef _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT
 
+struct __locale_guard {
+  _LIBCPP_HIDE_FROM_ABI __locale_guard(__locale_t __l) : __status(_configthreadlocale(_ENABLE_PER_THREAD_LOCALE)) {
+    // Setting the locale can be expensive even when the locale given is
+    // already the current locale, so do an explicit check to see if the
+    // current locale is already the one we want.
+    const char* __lc = __setlocale(nullptr);
+    // If every category is the same, the locale string will simply be the
+    // locale name, otherwise it will be a semicolon-separated string listing
+    // each category.  In the second case, we know at least one category won't
+    // be what we want, so we only have to check the first case.
+    if (std::strcmp(__l.__get_locale(), __lc) != 0) {
+      __locale_all = _strdup(__lc);
+      if (__locale_all == nullptr)
+        __throw_bad_alloc();
+      __setlocale(__l.__get_locale());
+    }
+  }
+  _LIBCPP_HIDE_FROM_ABI ~__locale_guard() {
+    // The CRT documentation doesn't explicitly say, but setlocale() does the
+    // right thing when given a semicolon-separated list of locale settings
+    // for the different categories in the same format as returned by
+    // setlocale(LC_ALL, nullptr).
+    if (__locale_all != nullptr) {
+      __setlocale(__locale_all);
+      free(__locale_all);
+    }
+    _configthreadlocale(__status);
+  }
+  _LIBCPP_HIDE_FROM_ABI static const char* __setlocale(const char* __locale) {
+    const char* __new_locale = setlocale(LC_ALL, __locale);
+    if (__new_locale == nullptr)
+      __throw_bad_alloc();
+    return __new_locale;
+  }
+  int __status;
+  char* __locale_all = nullptr;
+};
+
 } // namespace __locale
 _LIBCPP_END_NAMESPACE_STD
 

libcxx/include/__locale_dir/support/windows.h

@@ -21,8 +21,6 @@ inline _LIBCPP_HIDE_FROM_ABI void freelocale(locale_t) {}
 
 inline _LIBCPP_HIDE_FROM_ABI locale_t newlocale(int, const char*, locale_t) { return nullptr; }
 
-inline _LIBCPP_HIDE_FROM_ABI locale_t uselocale(locale_t) { return nullptr; }
-
 #define LC_COLLATE_MASK (1 << LC_COLLATE)
 #define LC_CTYPE_MASK (1 << LC_CTYPE)
 #define LC_MESSAGES_MASK (1 << LC_MESSAGES)

libcxx/include/__support/xlocale/__nop_locale_mgmt.h

@@ -1466,8 +1466,6 @@ module std [system] {
 
   module locale {
     header "locale"
-
-    module locale_guard   { header "__locale_dir/locale_guard.h" }
     module pad_and_output { header "__locale_dir/pad_and_output.h" }
 
     module support {

libcxx/include/module.modulemap

@@ -11,10 +11,6 @@
 #include <new>
 #include <string>
 
-#ifdef _LIBCPP_MSVCRT_LIKE
-#  include <__locale_dir/locale_guard.h>
-#endif
-
 #define _str(s) #s
 #define str(s) _str(s)
 #define _LIBCPP_ABI_NAMESPACE_STR str(_LIBCPP_ABI_NAMESPACE)
@@ -109,7 +105,7 @@ static void force_locale_initialization() {
   static bool once = []() {
     auto loc = __locale::__newlocale(LC_ALL_MASK, "C", 0);
     {
-      __locale_guard g(loc); // forces initialization of locale TLS
+      __locale::__locale_guard g(loc); // forces initialization of locale TLS
       ((void)g);
     }
     __locale::__freelocale(loc);

libcxx/src/iostream.cpp

@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__locale_dir/locale_guard.h>
 #include <__locale_dir/support/windows.h>
 #include <clocale> // std::localeconv() & friends
 #include <cstdarg> // va_start & friends
@@ -28,7 +27,7 @@ __locale_t __newlocale(int /*mask*/, const char* locale, __locale_t /*base*/) {
 }
 
 lconv* __localeconv(__locale_t& loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   lconv* lc = std::localeconv();
   if (!lc)
     return lc;
@@ -40,12 +39,12 @@ lconv* __localeconv(__locale_t& loc) {
 //
 #if !defined(_LIBCPP_MSVCRT)
 float __strtof(const char* nptr, char** endptr, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::strtof(nptr, endptr);
 }
 
 long double __strtold(const char* nptr, char** endptr, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::strtold(nptr, endptr);
 }
 #endif
@@ -55,7 +54,7 @@ long double __strtold(const char* nptr, char** endptr, __locale_t loc) {
 //
 #if defined(__MINGW32__) && __MSVCRT_VERSION__ < 0x0800
 size_t __strftime(char* ret, size_t n, const char* format, const struct tm* tm, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::strftime(ret, n, format, tm);
 }
 #endif
@@ -67,18 +66,18 @@ decltype(MB_CUR_MAX) __mb_len_max(__locale_t __l) {
 #if defined(_LIBCPP_MSVCRT)
   return ::___mb_cur_max_l_func(__l);
 #else
-  std::__locale_guard __current(__l);
+  __locale_guard __current(__l);
   return MB_CUR_MAX;
 #endif
 }
 
 wint_t __btowc(int c, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::btowc(c);
 }
 
 int __wctob(wint_t c, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::wctob(c);
 }
 
@@ -88,12 +87,12 @@ size_t __wcsnrtombs(char* __restrict dst,
                     size_t len,
                     mbstate_t* __restrict ps,
                     __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return ::wcsnrtombs(dst, src, nwc, len, ps);
 }
 
 size_t __wcrtomb(char* __restrict s, wchar_t wc, mbstate_t* __restrict ps, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::wcrtomb(s, wc, ps);
 }
 
@@ -103,24 +102,24 @@ size_t __mbsnrtowcs(wchar_t* __restrict dst,
                     size_t len,
                     mbstate_t* __restrict ps,
                     __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return ::mbsnrtowcs(dst, src, nms, len, ps);
 }
 
 size_t
 __mbrtowc(wchar_t* __restrict pwc, const char* __restrict s, size_t n, mbstate_t* __restrict ps, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::mbrtowc(pwc, s, n, ps);
 }
 
 size_t __mbrlen(const char* __restrict s, size_t n, mbstate_t* __restrict ps, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::mbrlen(s, n, ps);
 }
 
 size_t __mbsrtowcs(
     wchar_t* __restrict dst, const char** __restrict src, size_t len, mbstate_t* __restrict ps, __locale_t loc) {
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return std::mbsrtowcs(dst, src, len, ps);
 }
 
@@ -132,7 +131,7 @@ int __snprintf(char* ret, size_t n, __locale_t loc, const char* format, ...) {
   int result = ::__stdio_common_vsprintf(
       _CRT_INTERNAL_LOCAL_PRINTF_OPTIONS | _CRT_INTERNAL_PRINTF_STANDARD_SNPRINTF_BEHAVIOR, ret, n, format, loc, ap);
 #else
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   _LIBCPP_DIAGNOSTIC_PUSH
   _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wformat-nonliteral")
   int result = std::vsnprintf(ret, n, format, ap);
@@ -178,7 +177,7 @@ int __libcpp_vasprintf(char** sptr, const char* __restrict format, va_list ap) {
 int __asprintf(char** ret, __locale_t loc, const char* format, ...) {
   va_list ap;
   va_start(ap, format);
-  std::__locale_guard __current(loc);
+  __locale_guard __current(loc);
   return __libcpp_vasprintf(ret, format, ap);
 }