Update version

Ignoring the `-Wconversion` diagnostic in `make_format_args` was
leaking out of the header, resulting in that warning being ignored in
downstream code that includes `fmt/base.h`.

Instead, we should `push`/`pop` the diagnostics to ensure this is
cleaned up.

.github/workflows/scorecard.yml

@@ -60,6 +60,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@51f77329afa6477de8c49fc9c7046c15b9a4e79d # v3.29.5
+        uses: github/codeql-action/upload-sarif@3599b3baa15b485a2e49ef411a7a4bb2452e7f93 # v3.29.5
         with:
           sarif_file: results.sarif

ChangeLog.md

@@ -1,3 +1,77 @@
+# 12.1.0 - 2025-10-29
+
+- Optimized `buffer::append`, resulting in up to ~16% improvement on spdlog
+  benchmarks (https://github.com/fmtlib/fmt/pull/4541). Thanks @fyrsta7.
+
+- Worked around an ABI incompatibility in `std::locale_ref` between clang and
+  gcc (https://github.com/fmtlib/fmt/issues/4573).
+
+- Made `std::variant` and `std::expected` formatters work with `format_as`
+  (https://github.com/fmtlib/fmt/issues/4574,
+  https://github.com/fmtlib/fmt/pull/4575). Thanks @phprus.
+
+- Made `fmt::join<string_view>` work with C++ modules
+  (https://github.com/fmtlib/fmt/issues/4379,
+  https://github.com/fmtlib/fmt/pull/4577). Thanks @Arghnews.
+
+- Exported `fmt::is_compiled_string` and `operator""_cf` from the module
+  (https://github.com/fmtlib/fmt/pull/4544). Thanks @CrackedMatter.
+
+- Fixed a compatibility issue with C++ modules in clang
+  (https://github.com/fmtlib/fmt/pull/4548). Thanks @tsarn.
+
+- Added support for cv-qualified types to the `std::optional` formatter
+  (https://github.com/fmtlib/fmt/issues/4561,
+  https://github.com/fmtlib/fmt/pull/4562). Thanks @OleksandrKvl.
+
+- Added demangling support (used in exception and `std::type_info` formatters)
+  for libc++ and clang-cl
+  (https://github.com/fmtlib/fmt/issues/4542,
+  https://github.com/fmtlib/fmt/pull/4560,
+  https://github.com/fmtlib/fmt/issues/4568,
+  https://github.com/fmtlib/fmt/pull/4571).
+  Thanks @FatihBAKIR and @rohitsutreja.
+
+- Switched to global `malloc`/`free` to enable allocator customization
+  (https://github.com/fmtlib/fmt/issues/4569,
+  https://github.com/fmtlib/fmt/pull/4570). Thanks @rohitsutreja.
+
+- Made the `FMT_USE_CONSTEVAL` macro configurable by users
+  (https://github.com/fmtlib/fmt/pull/4546). Thanks @SnapperTT.
+
+- Fixed compilation with locales disabled in the header-only mode
+  (https://github.com/fmtlib/fmt/issues/4550).
+
+- Fixed compilation with clang 21 and `-std=c++20`
+  (https://github.com/fmtlib/fmt/issues/4552).
+
+- Fixed a dynamic linking issue with clang-cl
+  (https://github.com/fmtlib/fmt/issues/4576,
+  https://github.com/fmtlib/fmt/pull/4584). Thanks @FatihBAKIR.
+
+- Fixed a warning suppression leakage on gcc
+  (https://github.com/fmtlib/fmt/pull/4588). Thanks @ZedThree.
+
+- Made more internal color APIs `constexpr`
+  (https://github.com/fmtlib/fmt/pull/4581). Thanks @ishani.
+
+- Fixed compatibility with clang as a host compiler for NVCC
+  (https://github.com/fmtlib/fmt/pull/4564). Thanks @valgur.
+
+- Fixed various warnings and lint issues
+  (https://github.com/fmtlib/fmt/issues/4565,
+  https://github.com/fmtlib/fmt/pull/4572,
+  https://github.com/fmtlib/fmt/pull/4557).
+  Thanks @LiangHuDream and @teruyamato0731.
+
+- Improved documentation
+  (https://github.com/fmtlib/fmt/issues/4549,
+  https://github.com/fmtlib/fmt/pull/4551,
+  https://github.com/fmtlib/fmt/issues/4566,
+  https://github.com/fmtlib/fmt/pull/4567,
+  https://github.com/fmtlib/fmt/pull/4578,).
+  Thanks @teruyamato0731, @petersteneteg and @zimmerman-dev.
+
 # 12.0.0 - 2025-09-17
 
 - Optimized the default floating point formatting

doc/api.md

@@ -708,3 +708,53 @@ following differences:
   `std::to_chars` which tries to generate the smallest number of characters
   (ignoring redundant digits and sign in exponent) and may procude more
   decimal digits than necessary.
+
+## Configuration Options
+
+{fmt} provides configuration via CMake options and preprocessor macros to
+enable or disable features and to optimize for binary size. For example, you
+can disable OS-specific APIs defined in `fmt/os.h` with `-DFMT_OS=OFF` when
+configuring CMake.
+
+### CMake Options
+
+- **`FMT_OS`**: When set to `OFF`, disables OS-specific APIs (`fmt/os.h`).
+- **`FMT_UNICODE`**: When set of `OFF`, disables Unicode support on
+  Windows/MSVC. Unicode support is always enabled on other platforms.
+
+### Macros
+
+- **`FMT_HEADER_ONLY`**: Enables the header-only mode when defined. It is an
+  alternative to using the `fmt::fmt-header-only` CMake target.
+  Default: not defined.
+
+- **`FMT_USE_EXCEPTIONS`**: Disables the use of exceptions when set to `0`.
+  Default: `1` (`0` if compiled with `-fno-exceptions`).
+
+- **`FMT_USE_LOCALE`**: When set to `0`, disables locale support.
+  Default: `1` (`0` when `FMT_OPTIMIZE_SIZE > 1`).
+
+- **`FMT_CUSTOM_ASSERT_FAIL`**: When set to `1`, allows users to provide a
+  custom `fmt::assert_fail` function which is called on assertion failures and,
+  if exceptions are disabled, on runtime errors. Default: `0`.
+
+- **`FMT_BUILTIN_TYPES`**: When set to `0`, disables built-in handling of
+  arithmetic and string types other than `int`. This reduces library size at
+  the cost of per-call overhead. Default: `1`.
+
+- **`FMT_OPTIMIZE_SIZE`**: Controls binary size optimizations:
+    - `0` - off (default)
+    - `1` - disables locale support and applies some optimizations
+    - `2` - disables some Unicode features, named arguments and applies more
+      aggresive optimizations
+
+### Binary Size Optimization
+
+To minimize the binary footprint of {fmt} as much as possible at the cost of
+some features, you can use the following configuration:
+
+- CMake options:
+    - `FMT_OS=OFF`
+- Macros:
+    - `FMT_BUILTIN_TYPES=0`
+    - `FMT_OPTIMIZE_SIZE=2`

doc/syntax.md

@@ -251,7 +251,7 @@ The available integer presentation types are:
   <td><code>'b'</code></td>
   <td>
     Binary format. Outputs the number in base 2. Using the <code>'#'</code>
-    option with this type adds the prefix <code>"0b"</code> to the output value.    
+    option with this type adds the prefix <code>"0b"</code> to the output value.
   </td>
 </tr>
 <tr>
@@ -718,7 +718,7 @@ These modifiers are only supported for the `'H'`, `'I'`, `'M'`, `'S'`, `'U'`,
 Format specifications for range types have the following syntax:
 
 <pre><code class="language-json"
->range_format_spec ::= ["n"][range_type][range_underlying_spec]</code>
+>range_format_spec ::= ["n"][range_type][":" range_underlying_spec]</code>
 </pre>
 
 The `'n'` option formats the range without the opening and closing brackets.
@@ -761,14 +761,16 @@ fmt::print("{::}", std::vector{'h', 'e', 'l', 'l', 'o'});
 // Output: [h, e, l, l, o]
 fmt::print("{::d}", std::vector{'h', 'e', 'l', 'l', 'o'});
 // Output: [104, 101, 108, 108, 111]
+fmt::print("{:n:f}", std::array{std::numbers::pi, std::numbers::e});
+// Output: 3.141593, 2.718282
 ```
 
 ## Format Examples
 
 This section contains examples of the format syntax and comparison with
-the printf formatting.
+the `printf` formatting.
 
-In most of the cases the syntax is similar to the printf formatting,
+In most of the cases the syntax is similar to the `printf` formatting,
 with the addition of the `{}` and with `:` used instead of `%`. For
 example, `"%03.2f"` can be translated to `"{:03.2f}"`.
 

include/fmt/base.h

@@ -21,7 +21,7 @@
 #endif
 
 // The fmt library version in the form major * 10000 + minor * 100 + patch.
-#define FMT_VERSION 120000
+#define FMT_VERSION 120100
 
 // Detect compiler versions.
 #if defined(__clang__) && !defined(__ibmxl__)
@@ -114,7 +114,9 @@
 #endif
 
 // Detect consteval, C++20 constexpr extensions and std::is_constant_evaluated.
-#if !defined(__cpp_lib_is_constant_evaluated)
+#ifdef FMT_USE_CONSTEVAL
+// Use the provided definition.
+#elif !defined(__cpp_lib_is_constant_evaluated)
 #  define FMT_USE_CONSTEVAL 0
 #elif FMT_CPLUSPLUS < 201709L
 #  define FMT_USE_CONSTEVAL 0
@@ -234,6 +236,7 @@ FMT_PRAGMA_GCC(optimize("Og"))
 #  define FMT_GCC_OPTIMIZED
 #endif
 FMT_PRAGMA_CLANG(diagnostic push)
+FMT_PRAGMA_GCC(diagnostic push)
 
 #ifdef FMT_ALWAYS_INLINE
 // Use the provided definition.
@@ -414,8 +417,12 @@ inline auto map(int128_opt) -> monostate { return {}; }
 inline auto map(uint128_opt) -> monostate { return {}; }
 #endif
 
-#ifndef FMT_USE_BITINT
-#  define FMT_USE_BITINT (FMT_CLANG_VERSION >= 1500)
+#ifdef FMT_USE_BITINT
+// Use the provided definition.
+#elif FMT_CLANG_VERSION >= 1500 && !defined(__CUDACC__)
+#  define FMT_USE_BITINT 1
+#else
+#  define FMT_USE_BITINT 0
 #endif
 
 #if FMT_USE_BITINT
@@ -918,7 +925,10 @@ class locale_ref {
   constexpr locale_ref() : locale_(nullptr) {}
 
   template <typename Locale, FMT_ENABLE_IF(sizeof(Locale::collate) != 0)>
-  locale_ref(const Locale& loc);
+  locale_ref(const Locale& loc) : locale_(&loc) {
+    // Check if std::isalpha is found via ADL to reduce the chance of misuse.
+    isalpha('x', loc);
+  }
 
   inline explicit operator bool() const noexcept { return locale_ != nullptr; }
 #endif  // FMT_USE_LOCALE
@@ -1844,12 +1854,17 @@ template <typename T> class buffer {
       void
       append(const U* begin, const U* end) {
     while (begin != end) {
+      auto size = size_;
+      auto free_cap = capacity_ - size;
       auto count = to_unsigned(end - begin);
-      try_reserve(size_ + count);
-      auto free_cap = capacity_ - size_;
-      if (free_cap < count) count = free_cap;
+      if (free_cap < count) {
+        grow_(*this, size + count);
+        size = size_;
+        free_cap = capacity_ - size;
+        count = count < free_cap ? count : free_cap;
+      }
       // A loop is faster than memcpy on small sizes.
-      T* out = ptr_ + size_;
+      T* out = ptr_ + size;
       for (size_t i = 0; i < count; ++i) out[i] = begin[i];
       size_ += count;
       begin += count;
@@ -2983,6 +2998,7 @@ FMT_INLINE void println(format_string<T...> fmt, T&&... args) {
   return fmt::println(stdout, fmt, static_cast<T&&>(args)...);
 }
 
+FMT_PRAGMA_GCC(diagnostic pop)
 FMT_PRAGMA_CLANG(diagnostic pop)
 FMT_PRAGMA_GCC(pop_options)
 FMT_END_EXPORT

include/fmt/chrono.h

@@ -1594,8 +1594,13 @@ class get_locale {
 
  public:
   inline get_locale(bool localized, locale_ref loc) : has_locale_(localized) {
-    if (localized)
-      ::new (&locale_) std::locale(loc.template get<std::locale>());
+    if (!localized) return;
+    ignore_unused(loc);
+    ::new (&locale_) std::locale(
+#if FMT_USE_LOCALE
+        loc.template get<std::locale>()
+#endif
+    );
   }
   inline ~get_locale() {
     if (has_locale_) locale_.~locale();

include/fmt/color.h

@@ -429,7 +429,7 @@ template <typename Char> struct ansi_color_escape {
 
  private:
   static constexpr size_t num_emphases = 8;
-  Char buffer[7u + 4u * num_emphases];
+  Char buffer[7u + 4u * num_emphases] = {};
   size_t size = 0;
 
   static FMT_CONSTEXPR void to_esc(uint8_t c, Char* out,

include/fmt/compile.h

@@ -15,9 +15,10 @@
 #include "format.h"
 
 FMT_BEGIN_NAMESPACE
+FMT_BEGIN_EXPORT
 
 // A compile-time string which is compiled into fast formatting code.
-FMT_EXPORT class compiled_string {};
+class compiled_string {};
 
 template <typename S>
 struct is_compiled_string : std::is_base_of<compiled_string, S> {};
@@ -59,6 +60,8 @@ template <detail::fixed_string Str> constexpr auto operator""_cf() {
 }  // namespace literals
 #endif
 
+FMT_END_EXPORT
+
 namespace detail {
 
 template <typename T, typename... Tail>

include/fmt/format-inl.h

@@ -36,7 +36,7 @@ FMT_BEGIN_NAMESPACE
 FMT_FUNC void assert_fail(const char* file, int line, const char* message) {
   // Use unchecked std::fprintf to avoid triggering another assertion when
   // writing to stderr fails.
-  fprintf(stderr, "%s:%d: assertion failed: %s", file, line, message);
+  std::fprintf(stderr, "%s:%d: assertion failed: %s", file, line, message);
   abort();
 }
 #endif
@@ -47,11 +47,6 @@ using std::locale;
 using std::numpunct;
 using std::use_facet;
 }  // namespace detail
-
-template <typename Locale, enable_if_t<(sizeof(Locale::collate) != 0), int>>
-locale_ref::locale_ref(const Locale& loc) : locale_(&loc) {
-  static_assert(std::is_same<Locale, std::locale>::value, "");
-}
 #else
 namespace detail {
 struct locale {};

include/fmt/format.h

@@ -40,11 +40,18 @@
 
 #include "base.h"
 
+// libc++ supports string_view in pre-c++17.
+#if FMT_HAS_INCLUDE(<string_view>) && \
+    (FMT_CPLUSPLUS >= 201703L || defined(_LIBCPP_VERSION))
+#  define FMT_USE_STRING_VIEW
+#endif
+
 #ifndef FMT_MODULE
+#  include <stdlib.h>  // malloc, free
+
 #  include <cmath>    // std::signbit
 #  include <cstddef>  // std::byte
 #  include <cstdint>  // uint32_t
-#  include <cstdlib>  // std::malloc, std::free
 #  include <cstring>  // std::memcpy
 #  include <limits>   // std::numeric_limits
 #  include <new>      // std::bad_alloc
@@ -61,11 +68,8 @@
 #    include <bit>  // std::bit_cast
 #  endif
 
-// libc++ supports string_view in pre-c++17.
-#  if FMT_HAS_INCLUDE(<string_view>) && \
-      (FMT_CPLUSPLUS >= 201703L || defined(_LIBCPP_VERSION))
+#  if defined(FMT_USE_STRING_VIEW)
 #    include <string_view>
-#    define FMT_USE_STRING_VIEW
 #  endif
 
 #  if FMT_MSC_VERSION
@@ -744,12 +748,12 @@ template <typename T> struct allocator : private std::decay<void> {
 
   auto allocate(size_t n) -> T* {
     FMT_ASSERT(n <= max_value<size_t>() / sizeof(T), "");
-    T* p = static_cast<T*>(std::malloc(n * sizeof(T)));
+    T* p = static_cast<T*>(malloc(n * sizeof(T)));
     if (!p) FMT_THROW(std::bad_alloc());
     return p;
   }
 
-  void deallocate(T* p, size_t) { std::free(p); }
+  void deallocate(T* p, size_t) { free(p); }
 
   constexpr friend auto operator==(allocator, allocator) noexcept -> bool {
     return true;  // All instances of this allocator are equivalent.
@@ -759,6 +763,14 @@ template <typename T> struct allocator : private std::decay<void> {
   }
 };
 
+template <typename Formatter>
+FMT_CONSTEXPR auto maybe_set_debug_format(Formatter& f, bool set)
+    -> decltype(f.set_debug_format(set)) {
+  f.set_debug_format(set);
+}
+template <typename Formatter>
+FMT_CONSTEXPR void maybe_set_debug_format(Formatter&, ...) {}
+
 }  // namespace detail
 
 FMT_BEGIN_EXPORT
@@ -2506,7 +2518,7 @@ FMT_CONSTEXPR20 auto write_fixed(OutputIt out, const DecimalFP& f,
     auto grouping = Grouping(loc, specs.localized());
     size += grouping.count_separators(exp);
     return write_padded<Char, align::right>(
-        out, specs, to_unsigned(size), [&](iterator it) {
+        out, specs, static_cast<size_t>(size), [&](iterator it) {
           if (s != sign::none) *it++ = detail::getsign<Char>(s);
           it = write_significand<Char>(it, f.significand, significand_size,
                                        f.exponent, grouping);

include/fmt/os.h

@@ -136,10 +136,9 @@ FMT_API std::system_error vwindows_error(int error_code, string_view fmt,
  * **Example**:
  *
  *     // This throws a system_error with the description
- *     //   cannot open file 'madeup': The system cannot find the file
- * specified.
- *     // or similar (system message may vary).
- *     const char *filename = "madeup";
+ *     //   cannot open file 'foo': The system cannot find the file specified.
+ *     // or similar (system message may vary) if the file doesn't exist.
+ *     const char *filename = "foo";
  *     LPOFSTRUCT of = LPOFSTRUCT();
  *     HFILE file = OpenFile(filename, &of, OF_READ);
  *     if (file == HFILE_ERROR) {
@@ -365,17 +364,17 @@ FMT_INLINE_VARIABLE constexpr auto buffer_size = detail::buffer_size();
 
 /// A fast buffered output stream for writing from a single thread. Writing from
 /// multiple threads without external synchronization may result in a data race.
-class FMT_API ostream : private detail::buffer<char> {
+class ostream : private detail::buffer<char> {
  private:
   file file_;
 
-  ostream(cstring_view path, const detail::ostream_params& params);
+  FMT_API ostream(cstring_view path, const detail::ostream_params& params);
 
-  static void grow(buffer<char>& buf, size_t);
+  FMT_API static void grow(buffer<char>& buf, size_t);
 
  public:
-  ostream(ostream&& other) noexcept;
-  ~ostream();
+  FMT_API ostream(ostream&& other) noexcept;
+  FMT_API ~ostream();
 
   operator writer() {
     detail::buffer<char>& buf = *this;

include/fmt/ranges.h

@@ -18,6 +18,13 @@
 
 #include "format.h"
 
+#if FMT_HAS_CPP_ATTRIBUTE(clang::lifetimebound)
+#  define FMT_LIFETIMEBOUND [[clang::lifetimebound]]
+#else
+#  define FMT_LIFETIMEBOUND
+#endif
+FMT_PRAGMA_CLANG(diagnostic error "-Wreturn-stack-address")
+
 FMT_BEGIN_NAMESPACE
 
 FMT_EXPORT
@@ -234,14 +241,6 @@ using range_reference_type =
 template <typename Range>
 using uncvref_type = remove_cvref_t<range_reference_type<Range>>;
 
-template <typename Formatter>
-FMT_CONSTEXPR auto maybe_set_debug_format(Formatter& f, bool set)
-    -> decltype(f.set_debug_format(set)) {
-  f.set_debug_format(set);
-}
-template <typename Formatter>
-FMT_CONSTEXPR void maybe_set_debug_format(Formatter&, ...) {}
-
 template <typename T>
 struct range_format_kind_
     : std::integral_constant<range_format,
@@ -821,12 +820,12 @@ auto join(Range&& r, string_view sep)
  *
  * **Example**:
  *
- *     auto t = std::tuple<int, char>{1, 'a'};
+ *     auto t = std::tuple<int, char>(1, 'a');
  *     fmt::print("{}", fmt::join(t, ", "));
  *     // Output: 1, a
  */
 template <typename Tuple, FMT_ENABLE_IF(is_tuple_like<Tuple>::value)>
-FMT_CONSTEXPR auto join(const Tuple& tuple, string_view sep)
+FMT_CONSTEXPR auto join(const Tuple& tuple FMT_LIFETIMEBOUND, string_view sep)
     -> tuple_join_view<Tuple, char> {
   return {tuple, sep};
 }

include/fmt/std.h

@@ -111,12 +111,17 @@ void write_escaped_path(basic_memory_buffer<Char>& quoted,
 #endif  // FMT_CPP_LIB_FILESYSTEM
 
 #if defined(__cpp_lib_expected) || FMT_CPP_LIB_VARIANT
-template <typename Char, typename OutputIt, typename T>
-auto write_escaped_alternative(OutputIt out, const T& v) -> OutputIt {
+
+template <typename Char, typename OutputIt, typename T, typename FormatContext>
+auto write_escaped_alternative(OutputIt out, const T& v, FormatContext& ctx)
+    -> OutputIt {
   if constexpr (has_to_string_view<T>::value)
     return write_escaped_string<Char>(out, detail::to_string_view(v));
   if constexpr (std::is_same_v<T, Char>) return write_escaped_char(out, v);
-  return write<Char>(out, v);
+
+  formatter<std::remove_cv_t<T>, Char> underlying;
+  maybe_set_debug_format(underlying, true);
+  return underlying.format(v, ctx);
 }
 #endif
 
@@ -139,50 +144,39 @@ template <typename Variant, typename Char> class is_variant_formattable {
 #endif  // FMT_CPP_LIB_VARIANT
 
 #if FMT_USE_RTTI
-
-template <typename OutputIt>
-auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
-#  ifdef FMT_HAS_ABI_CXA_DEMANGLE
-  int status = 0;
-  size_t size = 0;
-  std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
-      abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);
-
-  string_view demangled_name_view;
-  if (demangled_name_ptr) {
-    demangled_name_view = demangled_name_ptr.get();
-
-    // Normalization of stdlib inline namespace names.
-    // libc++ inline namespaces.
-    //  std::__1::*       -> std::*
-    //  std::__1::__fs::* -> std::*
-    // libstdc++ inline namespaces.
-    //  std::__cxx11::*             -> std::*
-    //  std::filesystem::__cxx11::* -> std::filesystem::*
-    if (demangled_name_view.starts_with("std::")) {
-      char* begin = demangled_name_ptr.get();
-      char* to = begin + 5;  // std::
-      for (char *from = to, *end = begin + demangled_name_view.size();
-           from < end;) {
-        // This is safe, because demangled_name is NUL-terminated.
-        if (from[0] == '_' && from[1] == '_') {
-          char* next = from + 1;
-          while (next < end && *next != ':') next++;
-          if (next[0] == ':' && next[1] == ':') {
-            from = next + 2;
-            continue;
-          }
+inline auto normalize_libcxx_inline_namespaces(string_view demangled_name_view,
+                                               char* begin) -> string_view {
+  // Normalization of stdlib inline namespace names.
+  // libc++ inline namespaces.
+  //  std::__1::*       -> std::*
+  //  std::__1::__fs::* -> std::*
+  // libstdc++ inline namespaces.
+  //  std::__cxx11::*             -> std::*
+  //  std::filesystem::__cxx11::* -> std::filesystem::*
+  if (demangled_name_view.starts_with("std::")) {
+    char* to = begin + 5;  // std::
+    for (const char *from = to, *end = begin + demangled_name_view.size();
+         from < end;) {
+      // This is safe, because demangled_name is NUL-terminated.
+      if (from[0] == '_' && from[1] == '_') {
+        const char* next = from + 1;
+        while (next < end && *next != ':') next++;
+        if (next[0] == ':' && next[1] == ':') {
+          from = next + 2;
+          continue;
         }
-        *to++ = *from++;
       }
-      demangled_name_view = {begin, detail::to_unsigned(to - begin)};
+      *to++ = *from++;
     }
-  } else {
-    demangled_name_view = string_view(ti.name());
+    demangled_name_view = {begin, detail::to_unsigned(to - begin)};
   }
-  return detail::write_bytes<char>(out, demangled_name_view);
-#  elif FMT_MSC_VERSION
-  const string_view demangled_name(ti.name());
+  return demangled_name_view;
+}
+
+template <class OutputIt>
+auto normalize_msvc_abi_name(string_view abi_name_view, OutputIt out)
+    -> OutputIt {
+  const string_view demangled_name(abi_name_view);
   for (size_t i = 0; i < demangled_name.size(); ++i) {
     auto sub = demangled_name;
     sub.remove_prefix(i);
@@ -201,6 +195,39 @@ auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
     if (*sub.begin() != ' ') *out++ = *sub.begin();
   }
   return out;
+}
+
+template <typename OutputIt>
+auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
+#  ifdef FMT_HAS_ABI_CXA_DEMANGLE
+  int status = 0;
+  size_t size = 0;
+  std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
+      abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &free);
+
+  string_view demangled_name_view;
+  if (demangled_name_ptr) {
+    demangled_name_view = normalize_libcxx_inline_namespaces(
+        demangled_name_ptr.get(), demangled_name_ptr.get());
+  } else {
+    demangled_name_view = string_view(ti.name());
+  }
+  return detail::write_bytes<char>(out, demangled_name_view);
+#  elif FMT_MSC_VERSION && defined(_MSVC_STL_UPDATE)
+  return normalize_msvc_abi_name(ti.name(), out);
+#  elif FMT_MSC_VERSION && defined(_LIBCPP_VERSION)
+  const string_view demangled_name = ti.name();
+  std::string name_copy(demangled_name.size(), '\0');
+  // normalize_msvc_abi_name removes class, struct, union etc that MSVC has in
+  // front of types
+  name_copy.erase(normalize_msvc_abi_name(demangled_name, name_copy.begin()),
+                  name_copy.end());
+  // normalize_libcxx_inline_namespaces removes the inline __1, __2, etc
+  // namespaces libc++ uses for ABI versioning On MSVC ABI + libc++
+  // environments, we need to eliminate both of them.
+  const string_view normalized_name =
+      normalize_libcxx_inline_namespaces(name_copy, name_copy.data());
+  return detail::write_bytes<char>(out, normalized_name);
 #  else
   return detail::write_bytes<char>(out, string_view(ti.name()));
 #  endif
@@ -255,21 +282,6 @@ template <typename T> auto ptr(const std::shared_ptr<T>& p) -> const void* {
 
 #if FMT_CPP_LIB_FILESYSTEM
 
-class path : public std::filesystem::path {
- public:
-  auto display_string() const -> std::string {
-    const std::filesystem::path& base = *this;
-    return fmt::format(FMT_STRING("{}"), base);
-  }
-  auto system_string() const -> std::string { return string(); }
-
-  auto generic_display_string() const -> std::string {
-    const std::filesystem::path& base = *this;
-    return fmt::format(FMT_STRING("{:g}"), base);
-  }
-  auto generic_system_string() const -> std::string { return generic_string(); }
-};
-
 template <typename Char> struct formatter<std::filesystem::path, Char> {
  private:
   format_specs specs_;
@@ -319,6 +331,21 @@ template <typename Char> struct formatter<std::filesystem::path, Char> {
   }
 };
 
+class path : public std::filesystem::path {
+ public:
+  auto display_string() const -> std::string {
+    const std::filesystem::path& base = *this;
+    return fmt::format(FMT_STRING("{}"), base);
+  }
+  auto system_string() const -> std::string { return string(); }
+
+  auto generic_display_string() const -> std::string {
+    const std::filesystem::path& base = *this;
+    return fmt::format(FMT_STRING("{:g}"), base);
+  }
+  auto generic_system_string() const -> std::string { return generic_string(); }
+};
+
 #endif  // FMT_CPP_LIB_FILESYSTEM
 
 template <size_t N, typename Char>
@@ -353,25 +380,16 @@ template <typename T, typename Char>
 struct formatter<std::optional<T>, Char,
                  std::enable_if_t<is_formattable<T, Char>::value>> {
  private:
-  formatter<T, Char> underlying_;
+  formatter<std::remove_cv_t<T>, Char> underlying_;
   static constexpr basic_string_view<Char> optional =
       detail::string_literal<Char, 'o', 'p', 't', 'i', 'o', 'n', 'a', 'l',
                              '('>{};
   static constexpr basic_string_view<Char> none =
       detail::string_literal<Char, 'n', 'o', 'n', 'e'>{};
 
-  template <class U>
-  FMT_CONSTEXPR static auto maybe_set_debug_format(U& u, bool set)
-      -> decltype(u.set_debug_format(set)) {
-    u.set_debug_format(set);
-  }
-
-  template <class U>
-  FMT_CONSTEXPR static void maybe_set_debug_format(U&, ...) {}
-
  public:
   FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) {
-    maybe_set_debug_format(underlying_, true);
+    detail::maybe_set_debug_format(underlying_, true);
     return underlying_.parse(ctx);
   }
 
@@ -407,10 +425,10 @@ struct formatter<std::expected<T, E>, Char,
     if (value.has_value()) {
       out = detail::write<Char>(out, "expected(");
       if constexpr (!std::is_void<T>::value)
-        out = detail::write_escaped_alternative<Char>(out, *value);
+        out = detail::write_escaped_alternative<Char>(out, *value, ctx);
     } else {
       out = detail::write<Char>(out, "unexpected(");
-      out = detail::write_escaped_alternative<Char>(out, value.error());
+      out = detail::write_escaped_alternative<Char>(out, value.error(), ctx);
     }
     *out++ = ')';
     return out;
@@ -474,7 +492,7 @@ struct formatter<Variant, Char,
     FMT_TRY {
       std::visit(
           [&](const auto& v) {
-            out = detail::write_escaped_alternative<Char>(out, v);
+            out = detail::write_escaped_alternative<Char>(out, v, ctx);
           },
           value);
     }
@@ -495,6 +513,8 @@ template <> struct formatter<std::error_code> {
   bool debug_ = false;
 
  public:
+  FMT_CONSTEXPR void set_debug_format(bool set = true) { debug_ = set; }
+
   FMT_CONSTEXPR auto parse(parse_context<>& ctx) -> const char* {
     auto it = ctx.begin(), end = ctx.end();
     if (it == end) return it;

src/format.cc

@@ -10,7 +10,7 @@
 FMT_BEGIN_NAMESPACE
 
 #if FMT_USE_LOCALE
-template FMT_API locale_ref::locale_ref(const std::locale& loc);
+template FMT_API locale_ref::locale_ref(const std::locale& loc);  // DEPRECATED!
 template FMT_API auto locale_ref::get<std::locale>() const -> std::locale;
 #endif
 

support/mkdocs

@@ -2,6 +2,10 @@
 # A script to invoke mkdocs with the correct environment.
 # Additionally supports deploying via mike:
 #   ./mkdocs deploy [mike-deploy-options]
+# For example:
+#   ./mkdocs deploy <version>
+# This will checkout the website to fmt/build/fmt.dev and deploy documentation
+# <version> there.
 
 import errno, os, shutil, sys
 from subprocess import call
@@ -40,7 +44,7 @@ config_path = os.path.join(support_dir, 'mkdocs.yml')
 args = sys.argv[1:]
 if len(args) > 0:
   command = args[0]
-  if command == 'deploy':
+  if command == 'deploy' or command == 'set-default':
     git_url = 'https://github.com/' if 'CI' in os.environ else 'git@github.com:'
     site_repo = git_url + 'fmtlib/fmt.dev.git'
 
@@ -64,14 +68,18 @@ if len(args) > 0:
     if ret != 0 or version == 'dev':
       sys.exit(ret)
     current_doc_path = os.path.join(site_dir, version)
-    os.makedirs(current_doc_path, exist_ok=True)
-    redirect_page_path = os.path.join(current_doc_path, 'api.html')
-    with open(redirect_page_path, "w") as file:
-      file.write(redirect_page)
-    ret = call(['git', 'add', redirect_page_path], cwd=site_dir)
-    if ret != 0:
-      sys.exit(ret)
-    ret = call(['git', 'commit', '--amend', '--no-edit'], cwd=site_dir)
+    # mike stages files added by deploy for deletion for unclear reason,
+    # undo it.
+    ret = call(['git', 'reset', '--hard'], cwd=site_dir)
+    if False:
+      os.makedirs(current_doc_path, exist_ok=True)
+      redirect_page_path = os.path.join(current_doc_path, 'api.html')
+      with open(redirect_page_path, "w") as file:
+        file.write(redirect_page)
+      ret = call(['git', 'add', redirect_page_path], cwd=site_dir)
+      if ret != 0:
+        sys.exit(ret)
+      ret = call(['git', 'commit', '--amend', '--no-edit'], cwd=site_dir)
     sys.exit(ret)
   elif not command.startswith('-'):
     args += ['-f', config_path]

test/std-test.cc

@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "fmt/os.h"       // fmt::system_category
+#include "fmt/ranges.h"
 #include "gtest-extra.h"  // StartsWith
 
 #ifdef __cpp_lib_filesystem
@@ -145,6 +146,7 @@ TEST(std_test, optional) {
   EXPECT_FALSE((fmt::is_formattable<unformattable>::value));
   EXPECT_FALSE((fmt::is_formattable<std::optional<unformattable>>::value));
   EXPECT_TRUE((fmt::is_formattable<std::optional<int>>::value));
+  EXPECT_TRUE((fmt::is_formattable<std::optional<const int>>::value));
 #endif
 }
 
@@ -196,7 +198,33 @@ class my_class {
     return fmt::to_string(elm.av);
   }
 };
+
+class my_class_int {
+ public:
+  int av;
+
+ private:
+  friend auto format_as(const my_class_int& elm) -> int { return elm.av; }
+};
 }  // namespace my_nso
+
+TEST(std_test, expected_format_as) {
+#ifdef __cpp_lib_expected
+  EXPECT_EQ(
+      fmt::format(
+          "{}", std::expected<my_nso::my_number, int>{my_nso::my_number::one}),
+      "expected(\"first\")");
+  EXPECT_EQ(
+      fmt::format("{}",
+                  std::expected<my_nso::my_class, int>{my_nso::my_class{7}}),
+      "expected(\"7\")");
+  EXPECT_EQ(fmt::format("{}",
+                        std::expected<my_nso::my_class_int, int>{
+                            my_nso::my_class_int{8}}),
+            "expected(8)");
+#endif
+}
+
 TEST(std_test, optional_format_as) {
 #ifdef __cpp_lib_optional
   EXPECT_EQ(fmt::format("{}", std::optional<my_nso::my_number>{}), "none");
@@ -205,6 +233,8 @@ TEST(std_test, optional_format_as) {
   EXPECT_EQ(fmt::format("{}", std::optional<my_nso::my_class>{}), "none");
   EXPECT_EQ(fmt::format("{}", std::optional{my_nso::my_class{7}}),
             "optional(\"7\")");
+  EXPECT_EQ(fmt::format("{}", std::optional{my_nso::my_class_int{8}}),
+            "optional(8)");
 #endif
 }
 
@@ -274,6 +304,24 @@ TEST(std_test, variant) {
 #endif
 }
 
+TEST(std_test, variant_format_as) {
+#ifdef __cpp_lib_variant
+
+  EXPECT_EQ(fmt::format("{}", std::variant<my_nso::my_number>{}),
+            "variant(\"first\")");
+  EXPECT_EQ(fmt::format(
+                "{}", std::variant<my_nso::my_number>{my_nso::my_number::one}),
+            "variant(\"first\")");
+  EXPECT_EQ(
+      fmt::format("{}", std::variant<my_nso::my_class>{my_nso::my_class{7}}),
+      "variant(\"7\")");
+  EXPECT_EQ(
+      fmt::format("{}",
+                  std::variant<my_nso::my_class_int>{my_nso::my_class_int{8}}),
+      "variant(8)");
+#endif
+}
+
 TEST(std_test, error_code) {
   auto& generic = std::generic_category();
   EXPECT_EQ(fmt::format("{}", std::error_code(42, generic)), "generic:42");
@@ -288,6 +336,10 @@ TEST(std_test, error_code) {
   EXPECT_EQ(fmt::format("{:s}", ec), ec.message());
   EXPECT_EQ(fmt::format("{:?}", std::error_code(42, generic)),
             "\"generic:42\"");
+  EXPECT_EQ(fmt::format("{}",
+                        std::map<std::error_code, int>{
+                            {std::error_code(42, generic), 0}}),
+            "{\"generic:42\": 0}");
 }
 
 template <typename Catch> void exception_test() {