Apply clang-tidy

12 files changed, 274 insertions, 241 deletions

diff --git a/include/fmt/args.h b/include/fmt/args.h
index 2d684e7c..ad1654bb 100644
--- a/include/fmt/args.h
+++ b/include/fmt/args.h
@@ -22,8 +22,9 @@ template <typename T> struct is_reference_wrapper : std::false_type {};
 template <typename T>
 struct is_reference_wrapper<std::reference_wrapper<T>> : std::true_type {};
 
-template <typename T> const T& unwrap(const T& v) { return v; }
-template <typename T> const T& unwrap(const std::reference_wrapper<T>& v) {
+template <typename T> auto unwrap(const T& v) -> const T& { return v; }
+template <typename T>
+auto unwrap(const std::reference_wrapper<T>& v) -> const T& {
   return static_cast<const T&>(v);
 }
 
@@ -50,7 +51,7 @@ class dynamic_arg_list {
   std::unique_ptr<node<>> head_;
 
  public:
-  template <typename T, typename Arg> const T& push(const Arg& arg) {
+  template <typename T, typename Arg> auto push(const Arg& arg) -> const T& {
     auto new_node = std::unique_ptr<typed_node<T>>(new typed_node<T>(arg));
     auto& value = new_node->value;
     new_node->next = std::move(head_);
@@ -110,14 +111,14 @@ class dynamic_format_arg_store
 
   friend class basic_format_args<Context>;
 
-  unsigned long long get_types() const {
+  auto get_types() const -> unsigned long long {
     return detail::is_unpacked_bit | data_.size() |
            (named_info_.empty()
                 ? 0ULL
                 : static_cast<unsigned long long>(detail::has_named_args_bit));
   }
 
-  const basic_format_arg<Context>* data() const {
+  auto data() const -> const basic_format_arg<Context>* {
     return named_info_.empty() ? data_.data() : data_.data() + 1;
   }
 
diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index bed584b6..1a4b7d5a 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -72,7 +72,8 @@ template <typename To, typename From,
           FMT_ENABLE_IF(!std::is_same<From, To>::value &&
                         std::numeric_limits<From>::is_signed ==
                             std::numeric_limits<To>::is_signed)>
-FMT_CONSTEXPR To lossless_integral_conversion(const From from, int& ec) {
+FMT_CONSTEXPR auto lossless_integral_conversion(const From from, int& ec)
+    -> To {
   ec = 0;
   using F = std::numeric_limits<From>;
   using T = std::numeric_limits<To>;
@@ -101,7 +102,8 @@ template <typename To, typename From,
           FMT_ENABLE_IF(!std::is_same<From, To>::value &&
                         std::numeric_limits<From>::is_signed !=
                             std::numeric_limits<To>::is_signed)>
-FMT_CONSTEXPR To lossless_integral_conversion(const From from, int& ec) {
+FMT_CONSTEXPR auto lossless_integral_conversion(const From from, int& ec)
+    -> To {
   ec = 0;
   using F = std::numeric_limits<From>;
   using T = std::numeric_limits<To>;
@@ -133,7 +135,8 @@ FMT_CONSTEXPR To lossless_integral_conversion(const From from, int& ec) {
 
 template <typename To, typename From,
           FMT_ENABLE_IF(std::is_same<From, To>::value)>
-FMT_CONSTEXPR To lossless_integral_conversion(const From from, int& ec) {
+FMT_CONSTEXPR auto lossless_integral_conversion(const From from, int& ec)
+    -> To {
   ec = 0;
   return from;
 }  // function
@@ -154,7 +157,7 @@ FMT_CONSTEXPR To lossless_integral_conversion(const From from, int& ec) {
 // clang-format on
 template <typename To, typename From,
           FMT_ENABLE_IF(!std::is_same<From, To>::value)>
-FMT_CONSTEXPR To safe_float_conversion(const From from, int& ec) {
+FMT_CONSTEXPR auto safe_float_conversion(const From from, int& ec) -> To {
   ec = 0;
   using T = std::numeric_limits<To>;
   static_assert(std::is_floating_point<From>::value, "From must be floating");
@@ -176,7 +179,7 @@ FMT_CONSTEXPR To safe_float_conversion(const From from, int& ec) {
 
 template <typename To, typename From,
           FMT_ENABLE_IF(std::is_same<From, To>::value)>
-FMT_CONSTEXPR To safe_float_conversion(const From from, int& ec) {
+FMT_CONSTEXPR auto safe_float_conversion(const From from, int& ec) -> To {
   ec = 0;
   static_assert(std::is_floating_point<From>::value, "From must be floating");
   return from;
@@ -188,8 +191,8 @@ FMT_CONSTEXPR To safe_float_conversion(const From from, int& ec) {
 template <typename To, typename FromRep, typename FromPeriod,
           FMT_ENABLE_IF(std::is_integral<FromRep>::value),
           FMT_ENABLE_IF(std::is_integral<typename To::rep>::value)>
-To safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
-                      int& ec) {
+auto safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
+                        int& ec) -> To {
   using From = std::chrono::duration<FromRep, FromPeriod>;
   ec = 0;
   // the basic idea is that we need to convert from count() in the from type
@@ -240,8 +243,8 @@ To safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
 template <typename To, typename FromRep, typename FromPeriod,
           FMT_ENABLE_IF(std::is_floating_point<FromRep>::value),
           FMT_ENABLE_IF(std::is_floating_point<typename To::rep>::value)>
-To safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
-                      int& ec) {
+auto safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
+                        int& ec) -> To {
   using From = std::chrono::duration<FromRep, FromPeriod>;
   ec = 0;
   if (std::isnan(from.count())) {
@@ -321,12 +324,12 @@ To safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
 
 namespace detail {
 template <typename T = void> struct null {};
-inline null<> localtime_r FMT_NOMACRO(...) { return null<>(); }
-inline null<> localtime_s(...) { return null<>(); }
-inline null<> gmtime_r(...) { return null<>(); }
-inline null<> gmtime_s(...) { return null<>(); }
+inline auto localtime_r FMT_NOMACRO(...) -> null<> { return null<>(); }
+inline auto localtime_s(...) -> null<> { return null<>(); }
+inline auto gmtime_r(...) -> null<> { return null<>(); }
+inline auto gmtime_s(...) -> null<> { return null<>(); }
 
-inline const std::locale& get_classic_locale() {
+inline auto get_classic_locale() -> const std::locale& {
   static const auto& locale = std::locale::classic();
   return locale;
 }
@@ -442,7 +445,7 @@ struct is_same_arithmetic_type
 template <
     typename To, typename FromRep, typename FromPeriod,
     FMT_ENABLE_IF(is_same_arithmetic_type<FromRep, typename To::rep>::value)>
-To fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) {
+auto fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
 #if FMT_SAFE_DURATION_CAST
   // Throwing version of safe_duration_cast is only available for
   // integer to integer or float to float casts.
@@ -459,14 +462,15 @@ To fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) {
 template <
     typename To, typename FromRep, typename FromPeriod,
     FMT_ENABLE_IF(!is_same_arithmetic_type<FromRep, typename To::rep>::value)>
-To fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) {
+auto fmt_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
   // Mixed integer <-> float cast is not supported by safe_duration_cast.
   return std::chrono::duration_cast<To>(from);
 }
 
 template <typename Duration>
-std::time_t to_time_t(
-    std::chrono::time_point<std::chrono::system_clock, Duration> time_point) {
+auto to_time_t(
+    std::chrono::time_point<std::chrono::system_clock, Duration> time_point)
+    -> std::time_t {
   // Cannot use std::chrono::system_clock::to_time_t since this would first
   // require a cast to std::chrono::system_clock::time_point, which could
   // overflow.
@@ -483,29 +487,29 @@ FMT_BEGIN_EXPORT
   expressed in local time. Unlike ``std::localtime``, this function is
   thread-safe on most platforms.
  */
-inline std::tm localtime(std::time_t time) {
+inline auto localtime(std::time_t time) -> std::tm {
   struct dispatcher {
     std::time_t time_;
     std::tm tm_;
 
     dispatcher(std::time_t t) : time_(t) {}
 
-    bool run() {
+    auto run() -> bool {
       using namespace fmt::detail;
       return handle(localtime_r(&time_, &tm_));
     }
 
-    bool handle(std::tm* tm) { return tm != nullptr; }
+    auto handle(std::tm* tm) -> bool { return tm != nullptr; }
 
-    bool handle(detail::null<>) {
+    auto handle(detail::null<>) -> bool {
       using namespace fmt::detail;
       return fallback(localtime_s(&tm_, &time_));
     }
 
-    bool fallback(int res) { return res == 0; }
+    auto fallback(int res) -> bool { return res == 0; }
 
 #if !FMT_MSC_VERSION
-    bool fallback(detail::null<>) {
+    auto fallback(detail::null<>) -> bool {
       using namespace fmt::detail;
       std::tm* tm = std::localtime(&time_);
       if (tm) tm_ = *tm;
@@ -532,29 +536,29 @@ inline auto localtime(std::chrono::local_time<Duration> time) -> std::tm {
   expressed in Coordinated Universal Time (UTC). Unlike ``std::gmtime``, this
   function is thread-safe on most platforms.
  */
-inline std::tm gmtime(std::time_t time) {
+inline auto gmtime(std::time_t time) -> std::tm {
   struct dispatcher {
     std::time_t time_;
     std::tm tm_;
 
     dispatcher(std::time_t t) : time_(t) {}
 
-    bool run() {
+    auto run() -> bool {
       using namespace fmt::detail;
       return handle(gmtime_r(&time_, &tm_));
     }
 
-    bool handle(std::tm* tm) { return tm != nullptr; }
+    auto handle(std::tm* tm) -> bool { return tm != nullptr; }
 
-    bool handle(detail::null<>) {
+    auto handle(detail::null<>) -> bool {
       using namespace fmt::detail;
       return fallback(gmtime_s(&tm_, &time_));
     }
 
-    bool fallback(int res) { return res == 0; }
+    auto fallback(int res) -> bool { return res == 0; }
 
 #if !FMT_MSC_VERSION
-    bool fallback(detail::null<>) {
+    auto fallback(detail::null<>) -> bool {
       std::tm* tm = std::gmtime(&time_);
       if (tm) tm_ = *tm;
       return tm != nullptr;
@@ -568,8 +572,9 @@ inline std::tm gmtime(std::time_t time) {
 }
 
 template <typename Duration>
-inline std::tm gmtime(
-    std::chrono::time_point<std::chrono::system_clock, Duration> time_point) {
+inline auto gmtime(
+    std::chrono::time_point<std::chrono::system_clock, Duration> time_point)
+    -> std::tm {
   return gmtime(detail::to_time_t(time_point));
 }
 
@@ -609,7 +614,8 @@ inline void write_digit2_separated(char* buf, unsigned a, unsigned b,
   }
 }
 
-template <typename Period> FMT_CONSTEXPR inline const char* get_units() {
+template <typename Period>
+FMT_CONSTEXPR inline auto get_units() -> const char* {
   if (std::is_same<Period, std::atto>::value) return "as";
   if (std::is_same<Period, std::femto>::value) return "fs";
   if (std::is_same<Period, std::pico>::value) return "ps";
@@ -665,9 +671,8 @@ auto write_padding(OutputIt out, pad_type pad) -> OutputIt {
 
 // Parses a put_time-like format string and invokes handler actions.
 template <typename Char, typename Handler>
-FMT_CONSTEXPR const Char* parse_chrono_format(const Char* begin,
-                                              const Char* end,
-                                              Handler&& handler) {
+FMT_CONSTEXPR auto parse_chrono_format(const Char* begin, const Char* end,
+                                       Handler&& handler) -> const Char* {
   if (begin == end || *begin == '}') return begin;
   if (*begin != '%') FMT_THROW(format_error("invalid format"));
   auto ptr = begin;
@@ -998,25 +1003,25 @@ struct tm_format_checker : null_chrono_spec_handler<tm_format_checker> {
   FMT_CONSTEXPR void on_tz_name() {}
 };
 
-inline const char* tm_wday_full_name(int wday) {
+inline auto tm_wday_full_name(int wday) -> const char* {
   static constexpr const char* full_name_list[] = {
       "Sunday",   "Monday", "Tuesday", "Wednesday",
       "Thursday", "Friday", "Saturday"};
   return wday >= 0 && wday <= 6 ? full_name_list[wday] : "?";
 }
-inline const char* tm_wday_short_name(int wday) {
+inline auto tm_wday_short_name(int wday) -> const char* {
   static constexpr const char* short_name_list[] = {"Sun", "Mon", "Tue", "Wed",
                                                     "Thu", "Fri", "Sat"};
   return wday >= 0 && wday <= 6 ? short_name_list[wday] : "???";
 }
 
-inline const char* tm_mon_full_name(int mon) {
+inline auto tm_mon_full_name(int mon) -> const char* {
   static constexpr const char* full_name_list[] = {
       "January", "February", "March",     "April",   "May",      "June",
       "July",    "August",   "September", "October", "November", "December"};
   return mon >= 0 && mon <= 11 ? full_name_list[mon] : "?";
 }
-inline const char* tm_mon_short_name(int mon) {
+inline auto tm_mon_short_name(int mon) -> const char* {
   static constexpr const char* short_name_list[] = {
       "Jan", "Feb", "Mar", "Apr", "May", "Jun",
       "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
@@ -1048,7 +1053,7 @@ inline void tzset_once() {
 
 // Converts value to Int and checks that it's in the range [0, upper).
 template <typename T, typename Int, FMT_ENABLE_IF(std::is_integral<T>::value)>
-inline Int to_nonnegative_int(T value, Int upper) {
+inline auto to_nonnegative_int(T value, Int upper) -> Int {
   if (!std::is_unsigned<Int>::value &&
       (value < 0 || to_unsigned(value) > to_unsigned(upper))) {
     FMT_THROW(fmt::format_error("chrono value is out of range"));
@@ -1056,13 +1061,13 @@ inline Int to_nonnegative_int(T value, Int upper) {
   return static_cast<Int>(value);
 }
 template <typename T, typename Int, FMT_ENABLE_IF(!std::is_integral<T>::value)>
-inline Int to_nonnegative_int(T value, Int upper) {
+inline auto to_nonnegative_int(T value, Int upper) -> Int {
   if (value < 0 || value > static_cast<T>(upper))
     FMT_THROW(format_error("invalid value"));
   return static_cast<Int>(value);
 }
 
-constexpr long long pow10(std::uint32_t n) {
+constexpr auto pow10(std::uint32_t n) -> long long {
   return n == 0 ? 1 : 10 * pow10(n - 1);
 }
 
@@ -1358,7 +1363,7 @@ class tm_writer {
         subsecs_(subsecs),
         tm_(tm) {}
 
-  OutputIt out() const { return out_; }
+  auto out() const -> OutputIt { return out_; }
 
   FMT_CONSTEXPR void on_text(const Char* begin, const Char* end) {
     out_ = copy_str<Char>(begin, end, out_);
@@ -1641,16 +1646,16 @@ struct chrono_format_checker : null_chrono_spec_handler<chrono_format_checker> {
 
 template <typename T,
           FMT_ENABLE_IF(std::is_integral<T>::value&& has_isfinite<T>::value)>
-inline bool isfinite(T) {
+inline auto isfinite(T) -> bool {
   return true;
 }
 
 template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
-inline T mod(T x, int y) {
+inline auto mod(T x, int y) -> T {
   return x % static_cast<T>(y);
 }
 template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value)>
-inline T mod(T x, int y) {
+inline auto mod(T x, int y) -> T {
   return std::fmod(x, static_cast<T>(y));
 }
 
@@ -1667,8 +1672,8 @@ template <typename T> struct make_unsigned_or_unchanged<T, true> {
 
 template <typename Rep, typename Period,
           FMT_ENABLE_IF(std::is_integral<Rep>::value)>
-inline std::chrono::duration<Rep, std::milli> get_milliseconds(
-    std::chrono::duration<Rep, Period> d) {
+inline auto get_milliseconds(std::chrono::duration<Rep, Period> d)
+    -> std::chrono::duration<Rep, std::milli> {
   // this may overflow and/or the result may not fit in the
   // target type.
 #if FMT_SAFE_DURATION_CAST
@@ -1690,13 +1695,13 @@ inline std::chrono::duration<Rep, std::milli> get_milliseconds(
 
 template <typename Char, typename Rep, typename OutputIt,
           FMT_ENABLE_IF(std::is_integral<Rep>::value)>
-OutputIt format_duration_value(OutputIt out, Rep val, int) {
+auto format_duration_value(OutputIt out, Rep val, int) -> OutputIt {
   return write<Char>(out, val);
 }
 
 template <typename Char, typename Rep, typename OutputIt,
           FMT_ENABLE_IF(std::is_floating_point<Rep>::value)>
-OutputIt format_duration_value(OutputIt out, Rep val, int precision) {
+auto format_duration_value(OutputIt out, Rep val, int precision) -> OutputIt {
   auto specs = format_specs<Char>();
   specs.precision = precision;
   specs.type = precision >= 0 ? presentation_type::fixed_lower
@@ -1705,12 +1710,12 @@ OutputIt format_duration_value(OutputIt out, Rep val, int precision) {
 }
 
 template <typename Char, typename OutputIt>
-OutputIt copy_unit(string_view unit, OutputIt out, Char) {
+auto copy_unit(string_view unit, OutputIt out, Char) -> OutputIt {
   return std::copy(unit.begin(), unit.end(), out);
 }
 
 template <typename OutputIt>
-OutputIt copy_unit(string_view unit, OutputIt out, wchar_t) {
+auto copy_unit(string_view unit, OutputIt out, wchar_t) -> OutputIt {
   // This works when wchar_t is UTF-32 because units only contain characters
   // that have the same representation in UTF-16 and UTF-32.
   utf8_to_utf16 u(unit);
@@ -1718,7 +1723,7 @@ OutputIt copy_unit(string_view unit, OutputIt out, wchar_t) {
 }
 
 template <typename Char, typename Period, typename OutputIt>
-OutputIt format_duration_unit(OutputIt out) {
+auto format_duration_unit(OutputIt out) -> OutputIt {
   if (const char* unit = get_units<Period>())
     return copy_unit(string_view(unit), out, Char());
   *out++ = '[';
@@ -1790,7 +1795,7 @@ struct chrono_formatter {
   }
 
   // returns true if nan or inf, writes to out.
-  bool handle_nan_inf() {
+  auto handle_nan_inf() -> bool {
     if (isfinite(val)) {
       return false;
     }
@@ -1807,18 +1812,22 @@ struct chrono_formatter {
     return true;
   }
 
-  Rep days() const { return static_cast<Rep>(s.count() / 86400); }
-  Rep hour() const { return static_cast<Rep>(mod((s.count() / 3600), 24)); }
+  auto days() const -> Rep { return static_cast<Rep>(s.count() / 86400); }
+  auto hour() const -> Rep {
+    return static_cast<Rep>(mod((s.count() / 3600), 24));
+  }
 
-  Rep hour12() const {
+  auto hour12() const -> Rep {
     Rep hour = static_cast<Rep>(mod((s.count() / 3600), 12));
     return hour <= 0 ? 12 : hour;
   }
 
-  Rep minute() const { return static_cast<Rep>(mod((s.count() / 60), 60)); }
-  Rep second() const { return static_cast<Rep>(mod(s.count(), 60)); }
+  auto minute() const -> Rep {
+    return static_cast<Rep>(mod((s.count() / 60), 60));
+  }
+  auto second() const -> Rep { return static_cast<Rep>(mod(s.count(), 60)); }
 
-  std::tm time() const {
+  auto time() const -> std::tm {
     auto time = std::tm();
     time.tm_hour = to_nonnegative_int(hour(), 24);
     time.tm_min = to_nonnegative_int(minute(), 60);
@@ -2000,7 +2009,7 @@ class weekday {
   weekday() = default;
   explicit constexpr weekday(unsigned wd) noexcept
       : value(static_cast<unsigned char>(wd != 7 ? wd : 0)) {}
-  constexpr unsigned c_encoding() const noexcept { return value; }
+  constexpr auto c_encoding() const noexcept -> unsigned { return value; }
 };
 
 class year_month_day {};
diff --git a/include/fmt/color.h b/include/fmt/color.h
index 34de634c..367849a8 100644
--- a/include/fmt/color.h
+++ b/include/fmt/color.h
@@ -233,7 +233,7 @@ class text_style {
   FMT_CONSTEXPR text_style(emphasis em = emphasis()) noexcept
       : set_foreground_color(), set_background_color(), ems(em) {}
 
-  FMT_CONSTEXPR text_style& operator|=(const text_style& rhs) {
+  FMT_CONSTEXPR auto operator|=(const text_style& rhs) -> text_style& {
     if (!set_foreground_color) {
       set_foreground_color = rhs.set_foreground_color;
       foreground_color = rhs.foreground_color;
@@ -257,29 +257,29 @@ class text_style {
     return *this;
   }
 
-  friend FMT_CONSTEXPR text_style operator|(text_style lhs,
-                                            const text_style& rhs) {
+  friend FMT_CONSTEXPR auto operator|(text_style lhs, const text_style& rhs)
+      -> text_style {
     return lhs |= rhs;
   }
 
-  FMT_CONSTEXPR bool has_foreground() const noexcept {
+  FMT_CONSTEXPR auto has_foreground() const noexcept -> bool {
     return set_foreground_color;
   }
-  FMT_CONSTEXPR bool has_background() const noexcept {
+  FMT_CONSTEXPR auto has_background() const noexcept -> bool {
     return set_background_color;
   }
-  FMT_CONSTEXPR bool has_emphasis() const noexcept {
+  FMT_CONSTEXPR auto has_emphasis() const noexcept -> bool {
     return static_cast<uint8_t>(ems) != 0;
   }
-  FMT_CONSTEXPR detail::color_type get_foreground() const noexcept {
+  FMT_CONSTEXPR auto get_foreground() const noexcept -> detail::color_type {
     FMT_ASSERT(has_foreground(), "no foreground specified for this style");
     return foreground_color;
   }
-  FMT_CONSTEXPR detail::color_type get_background() const noexcept {
+  FMT_CONSTEXPR auto get_background() const noexcept -> detail::color_type {
     FMT_ASSERT(has_background(), "no background specified for this style");
     return background_color;
   }
-  FMT_CONSTEXPR emphasis get_emphasis() const noexcept {
+  FMT_CONSTEXPR auto get_emphasis() const noexcept -> emphasis {
     FMT_ASSERT(has_emphasis(), "no emphasis specified for this style");
     return ems;
   }
@@ -297,9 +297,11 @@ class text_style {
     }
   }
 
-  friend FMT_CONSTEXPR text_style fg(detail::color_type foreground) noexcept;
+  friend FMT_CONSTEXPR auto fg(detail::color_type foreground) noexcept
+      -> text_style;
 
-  friend FMT_CONSTEXPR text_style bg(detail::color_type background) noexcept;
+  friend FMT_CONSTEXPR auto bg(detail::color_type background) noexcept
+      -> text_style;
 
   detail::color_type foreground_color;
   detail::color_type background_color;
@@ -309,16 +311,19 @@ class text_style {
 };
 
 /** Creates a text style from the foreground (text) color. */
-FMT_CONSTEXPR inline text_style fg(detail::color_type foreground) noexcept {
+FMT_CONSTEXPR inline auto fg(detail::color_type foreground) noexcept
+    -> text_style {
   return text_style(true, foreground);
 }
 
 /** Creates a text style from the background color. */
-FMT_CONSTEXPR inline text_style bg(detail::color_type background) noexcept {
+FMT_CONSTEXPR inline auto bg(detail::color_type background) noexcept
+    -> text_style {
   return text_style(false, background);
 }
 
-FMT_CONSTEXPR inline text_style operator|(emphasis lhs, emphasis rhs) noexcept {
+FMT_CONSTEXPR inline auto operator|(emphasis lhs, emphasis rhs) noexcept
+    -> text_style {
   return text_style(lhs) | rhs;
 }
 
@@ -384,8 +389,8 @@ template <typename Char> struct ansi_color_escape {
   }
   FMT_CONSTEXPR operator const Char*() const noexcept { return buffer; }
 
-  FMT_CONSTEXPR const Char* begin() const noexcept { return buffer; }
-  FMT_CONSTEXPR_CHAR_TRAITS const Char* end() const noexcept {
+  FMT_CONSTEXPR auto begin() const noexcept -> const Char* { return buffer; }
+  FMT_CONSTEXPR_CHAR_TRAITS auto end() const noexcept -> const Char* {
     return buffer + std::char_traits<Char>::length(buffer);
   }
 
@@ -400,25 +405,27 @@ template <typename Char> struct ansi_color_escape {
     out[2] = static_cast<Char>('0' + c % 10);
     out[3] = static_cast<Char>(delimiter);
   }
-  static FMT_CONSTEXPR bool has_emphasis(emphasis em, emphasis mask) noexcept {
+  static FMT_CONSTEXPR auto has_emphasis(emphasis em, emphasis mask) noexcept
+      -> bool {
     return static_cast<uint8_t>(em) & static_cast<uint8_t>(mask);
   }
 };
 
 template <typename Char>
-FMT_CONSTEXPR ansi_color_escape<Char> make_foreground_color(
-    detail::color_type foreground) noexcept {
+FMT_CONSTEXPR auto make_foreground_color(detail::color_type foreground) noexcept
+    -> ansi_color_escape<Char> {
   return ansi_color_escape<Char>(foreground, "\x1b[38;2;");
 }
 
 template <typename Char>
-FMT_CONSTEXPR ansi_color_escape<Char> make_background_color(
-    detail::color_type background) noexcept {
+FMT_CONSTEXPR auto make_background_color(detail::color_type background) noexcept
+    -> ansi_color_escape<Char> {
   return ansi_color_escape<Char>(background, "\x1b[48;2;");
 }
 
 template <typename Char>
-FMT_CONSTEXPR ansi_color_escape<Char> make_emphasis(emphasis em) noexcept {
+FMT_CONSTEXPR auto make_emphasis(emphasis em) noexcept
+    -> ansi_color_escape<Char> {
   return ansi_color_escape<Char>(em);
 }
 
@@ -511,9 +518,10 @@ void print(const text_style& ts, const S& format_str, const Args&... args) {
 }
 
 template <typename S, typename Char = char_t<S>>
-inline std::basic_string<Char> vformat(
+inline auto vformat(
     const text_style& ts, const S& format_str,
-    basic_format_args<buffer_context<type_identity_t<Char>>> args) {
+    basic_format_args<buffer_context<type_identity_t<Char>>> args)
+    -> std::basic_string<Char> {
   basic_memory_buffer<Char> buf;
   detail::vformat_to(buf, ts, detail::to_string_view(format_str), args);
   return fmt::to_string(buf);
@@ -532,8 +540,8 @@ inline std::basic_string<Char> vformat(
   \endrst
 */
 template <typename S, typename... Args, typename Char = char_t<S>>
-inline std::basic_string<Char> format(const text_style& ts, const S& format_str,
-                                      const Args&... args) {
+inline auto format(const text_style& ts, const S& format_str,
+                   const Args&... args) -> std::basic_string<Char> {
   return fmt::vformat(ts, detail::to_string_view(format_str),
                       fmt::make_format_args<buffer_context<Char>>(args...));
 }
@@ -543,9 +551,10 @@ inline std::basic_string<Char> format(const text_style& ts, const S& format_str,
  */
 template <typename OutputIt, typename Char,
           FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, Char>::value)>
-OutputIt vformat_to(
-    OutputIt out, const text_style& ts, basic_string_view<Char> format_str,
-    basic_format_args<buffer_context<type_identity_t<Char>>> args) {
+auto vformat_to(OutputIt out, const text_style& ts,
+                basic_string_view<Char> format_str,
+                basic_format_args<buffer_context<type_identity_t<Char>>> args)
+    -> OutputIt {
   auto&& buf = detail::get_buffer<Char>(out);
   detail::vformat_to(buf, ts, format_str, args);
   return detail::get_iterator(buf, out);
diff --git a/include/fmt/compile.h b/include/fmt/compile.h
index a4c7e495..067cb423 100644
--- a/include/fmt/compile.h
+++ b/include/fmt/compile.h
@@ -14,8 +14,8 @@ FMT_BEGIN_NAMESPACE
 namespace detail {
 
 template <typename Char, typename InputIt>
-FMT_CONSTEXPR inline counting_iterator copy_str(InputIt begin, InputIt end,
-                                                counting_iterator it) {
+FMT_CONSTEXPR inline auto copy_str(InputIt begin, InputIt end,
+                                   counting_iterator it) -> counting_iterator {
   return it + (end - begin);
 }
 
@@ -57,7 +57,7 @@ struct udl_compiled_string : compiled_string {
 #endif
 
 template <typename T, typename... Tail>
-const T& first(const T& value, const Tail&...) {
+auto first(const T& value, const Tail&...) -> const T& {
   return value;
 }
 
@@ -488,8 +488,8 @@ FMT_CONSTEXPR OutputIt format_to(OutputIt out, const S&, Args&&... args) {
 
 template <typename OutputIt, typename S, typename... Args,
           FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
-format_to_n_result<OutputIt> format_to_n(OutputIt out, size_t n,
-                                         const S& format_str, Args&&... args) {
+auto format_to_n(OutputIt out, size_t n, const S& format_str, Args&&... args)
+    -> format_to_n_result<OutputIt> {
   using traits = detail::fixed_buffer_traits;
   auto buf = detail::iterator_buffer<OutputIt, char, traits>(out, n);
   format_to(std::back_inserter(buf), format_str, std::forward<Args>(args)...);
@@ -498,8 +498,8 @@ format_to_n_result<OutputIt> format_to_n(OutputIt out, size_t n,
 
 template <typename S, typename... Args,
           FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
-FMT_CONSTEXPR20 size_t formatted_size(const S& format_str,
-                                      const Args&... args) {
+FMT_CONSTEXPR20 auto formatted_size(const S& format_str, const Args&... args)
+    -> size_t {
   return fmt::format_to(detail::counting_iterator(), format_str, args...)
       .count();
 }
diff --git a/include/fmt/core.h b/include/fmt/core.h
index 3b5bd9ae..ce9f0e70 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -471,15 +471,15 @@ template <typename Char> class basic_string_view {
     size_ -= n;
   }
 
-  FMT_CONSTEXPR_CHAR_TRAITS bool starts_with(
-      basic_string_view<Char> sv) const noexcept {
+  FMT_CONSTEXPR_CHAR_TRAITS auto starts_with(
+      basic_string_view<Char> sv) const noexcept -> bool {
     return size_ >= sv.size_ &&
            std::char_traits<Char>::compare(data_, sv.data_, sv.size_) == 0;
   }
-  FMT_CONSTEXPR_CHAR_TRAITS bool starts_with(Char c) const noexcept {
+  FMT_CONSTEXPR_CHAR_TRAITS auto starts_with(Char c) const noexcept -> bool {
     return size_ >= 1 && std::char_traits<Char>::eq(*data_, c);
   }
-  FMT_CONSTEXPR_CHAR_TRAITS bool starts_with(const Char* s) const {
+  FMT_CONSTEXPR_CHAR_TRAITS auto starts_with(const Char* s) const -> bool {
     return starts_with(basic_string_view<Char>(s));
   }
 
@@ -617,10 +617,10 @@ FMT_TYPE_CONSTANT(const Char*, cstring_type);
 FMT_TYPE_CONSTANT(basic_string_view<Char>, string_type);
 FMT_TYPE_CONSTANT(const void*, pointer_type);
 
-constexpr bool is_integral_type(type t) {
+constexpr auto is_integral_type(type t) -> bool {
   return t > type::none_type && t <= type::last_integer_type;
 }
-constexpr bool is_arithmetic_type(type t) {
+constexpr auto is_arithmetic_type(type t) -> bool {
   return t > type::none_type && t <= type::last_numeric_type;
 }
 
diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index bfd00566..bb40e62c 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -85,7 +85,7 @@ locale_ref::locale_ref(const Locale& loc) : locale_(&loc) {
   static_assert(std::is_same<Locale, std::locale>::value, "");
 }
 
-template <typename Locale> Locale locale_ref::get() const {
+template <typename Locale> auto locale_ref::get() const -> Locale {
   static_assert(std::is_same<Locale, std::locale>::value, "");
   return locale_ ? *static_cast<const std::locale*>(locale_) : std::locale();
 }
@@ -97,7 +97,8 @@ FMT_FUNC auto thousands_sep_impl(locale_ref loc) -> thousands_sep_result<Char> {
   auto thousands_sep = grouping.empty() ? Char() : facet.thousands_sep();
   return {std::move(grouping), thousands_sep};
 }
-template <typename Char> FMT_FUNC Char decimal_point_impl(locale_ref loc) {
+template <typename Char>
+FMT_FUNC auto decimal_point_impl(locale_ref loc) -> Char {
   return std::use_facet<std::numpunct<Char>>(loc.get<std::locale>())
       .decimal_point();
 }
@@ -143,24 +144,25 @@ FMT_API FMT_FUNC auto format_facet<std::locale>::do_put(
 }
 #endif
 
-FMT_FUNC std::system_error vsystem_error(int error_code, string_view fmt,
-                                         format_args args) {
+FMT_FUNC auto vsystem_error(int error_code, string_view fmt, format_args args)
+    -> std::system_error {
   auto ec = std::error_code(error_code, std::generic_category());
   return std::system_error(ec, vformat(fmt, args));
 }
 
 namespace detail {
 
-template <typename F> inline bool operator==(basic_fp<F> x, basic_fp<F> y) {
+template <typename F>
+inline auto operator==(basic_fp<F> x, basic_fp<F> y) -> bool {
   return x.f == y.f && x.e == y.e;
 }
 
 // Compilers should be able to optimize this into the ror instruction.
-FMT_CONSTEXPR inline uint32_t rotr(uint32_t n, uint32_t r) noexcept {
+FMT_CONSTEXPR inline auto rotr(uint32_t n, uint32_t r) noexcept -> uint32_t {
   r &= 31;
   return (n >> r) | (n << (32 - r));
 }
-FMT_CONSTEXPR inline uint64_t rotr(uint64_t n, uint32_t r) noexcept {
+FMT_CONSTEXPR inline auto rotr(uint64_t n, uint32_t r) noexcept -> uint64_t {
   r &= 63;
   return (n >> r) | (n << (64 - r));
 }
@@ -169,14 +171,14 @@ FMT_CONSTEXPR inline uint64_t rotr(uint64_t n, uint32_t r) noexcept {
 namespace dragonbox {
 // Computes upper 64 bits of multiplication of a 32-bit unsigned integer and a
 // 64-bit unsigned integer.
-inline uint64_t umul96_upper64(uint32_t x, uint64_t y) noexcept {
+inline auto umul96_upper64(uint32_t x, uint64_t y) noexcept -> uint64_t {
   return umul128_upper64(static_cast<uint64_t>(x) << 32, y);
 }
 
 // Computes lower 128 bits of multiplication of a 64-bit unsigned integer and a
 // 128-bit unsigned integer.
-inline uint128_fallback umul192_lower128(uint64_t x,
-                                         uint128_fallback y) noexcept {
+inline auto umul192_lower128(uint64_t x, uint128_fallback y) noexcept
+    -> uint128_fallback {
   uint64_t high = x * y.high();
   uint128_fallback high_low = umul128(x, y.low());
   return {high + high_low.high(), high_low.low()};
@@ -184,12 +186,12 @@ inline uint128_fallback umul192_lower128(uint64_t x,
 
 // Computes lower 64 bits of multiplication of a 32-bit unsigned integer and a
 // 64-bit unsigned integer.
-inline uint64_t umul96_lower64(uint32_t x, uint64_t y) noexcept {
+inline auto umul96_lower64(uint32_t x, uint64_t y) noexcept -> uint64_t {
   return x * y;
 }
 
 // Various fast log computations.
-inline int floor_log10_pow2_minus_log10_4_over_3(int e) noexcept {
+inline auto floor_log10_pow2_minus_log10_4_over_3(int e) noexcept -> int {
   FMT_ASSERT(e <= 2936 && e >= -2985, "too large exponent");
   return (e * 631305 - 261663) >> 21;
 }
@@ -203,7 +205,7 @@ FMT_INLINE_VARIABLE constexpr struct {
 // divisible by pow(10, N).
 // Precondition: n <= pow(10, N + 1).
 template <int N>
-bool check_divisibility_and_divide_by_pow10(uint32_t& n) noexcept {
+auto check_divisibility_and_divide_by_pow10(uint32_t& n) noexcept -> bool {
   // The numbers below are chosen such that:
   //   1. floor(n/d) = floor(nm / 2^k) where d=10 or d=100,
   //   2. nm mod 2^k < m if and only if n is divisible by d,
@@ -228,7 +230,7 @@ bool check_divisibility_and_divide_by_pow10(uint32_t& n) noexcept {
 
 // Computes floor(n / pow(10, N)) for small n and N.
 // Precondition: n <= pow(10, N + 1).
-template <int N> uint32_t small_division_by_pow10(uint32_t n) noexcept {
+template <int N> auto small_division_by_pow10(uint32_t n) noexcept -> uint32_t {
   constexpr auto info = div_small_pow10_infos[N - 1];
   FMT_ASSERT(n <= info.divisor * 10, "n is too large");
   constexpr uint32_t magic_number =
@@ -237,12 +239,12 @@ template <int N> uint32_t small_division_by_pow10(uint32_t n) noexcept {
 }
 
 // Computes floor(n / 10^(kappa + 1)) (float)
-inline uint32_t divide_by_10_to_kappa_plus_1(uint32_t n) noexcept {
+inline auto divide_by_10_to_kappa_plus_1(uint32_t n) noexcept -> uint32_t {
   // 1374389535 = ceil(2^37/100)
   return static_cast<uint32_t>((static_cast<uint64_t>(n) * 1374389535) >> 37);
 }
 // Computes floor(n / 10^(kappa + 1)) (double)
-inline uint64_t divide_by_10_to_kappa_plus_1(uint64_t n) noexcept {
+inline auto divide_by_10_to_kappa_plus_1(uint64_t n) noexcept -> uint64_t {
   // 2361183241434822607 = ceil(2^(64+7)/1000)
   return umul128_upper64(n, 2361183241434822607ull) >> 7;
 }
@@ -254,7 +256,7 @@ template <> struct cache_accessor<float> {
   using carrier_uint = float_info<float>::carrier_uint;
   using cache_entry_type = uint64_t;
 
-  static uint64_t get_cached_power(int k) noexcept {
+  static auto get_cached_power(int k) noexcept -> uint64_t {
     FMT_ASSERT(k >= float_info<float>::min_k && k <= float_info<float>::max_k,
                "k is out of range");
     static constexpr const uint64_t pow10_significands[] = {
@@ -296,20 +298,23 @@ template <> struct cache_accessor<float> {
     bool is_integer;
   };
 
-  static compute_mul_result compute_mul(
-      carrier_uint u, const cache_entry_type& cache) noexcept {
+  static auto compute_mul(carrier_uint u,
+                          const cache_entry_type& cache) noexcept
+      -> compute_mul_result {
     auto r = umul96_upper64(u, cache);
     return {static_cast<carrier_uint>(r >> 32),
             static_cast<carrier_uint>(r) == 0};
   }
 
-  static uint32_t compute_delta(const cache_entry_type& cache,
-                                int beta) noexcept {
+  static auto compute_delta(const cache_entry_type& cache, int beta) noexcept
+      -> uint32_t {
     return static_cast<uint32_t>(cache >> (64 - 1 - beta));
   }
 
-  static compute_mul_parity_result compute_mul_parity(
-      carrier_uint two_f, const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_mul_parity(carrier_uint two_f,
+                                 const cache_entry_type& cache,
+                                 int beta) noexcept
+      -> compute_mul_parity_result {
     FMT_ASSERT(beta >= 1, "");
     FMT_ASSERT(beta < 64, "");
 
@@ -318,22 +323,22 @@ template <> struct cache_accessor<float> {
             static_cast<uint32_t>(r >> (32 - beta)) == 0};
   }
 
-  static carrier_uint compute_left_endpoint_for_shorter_interval_case(
-      const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_left_endpoint_for_shorter_interval_case(
+      const cache_entry_type& cache, int beta) noexcept -> carrier_uint {
     return static_cast<carrier_uint>(
         (cache - (cache >> (num_significand_bits<float>() + 2))) >>
         (64 - num_significand_bits<float>() - 1 - beta));
   }
 
-  static carrier_uint compute_right_endpoint_for_shorter_interval_case(
-      const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_right_endpoint_for_shorter_interval_case(
+      const cache_entry_type& cache, int beta) noexcept -> carrier_uint {
     return static_cast<carrier_uint>(
         (cache + (cache >> (num_significand_bits<float>() + 1))) >>
         (64 - num_significand_bits<float>() - 1 - beta));
   }
 
-  static carrier_uint compute_round_up_for_shorter_interval_case(
-      const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_round_up_for_shorter_interval_case(
+      const cache_entry_type& cache, int beta) noexcept -> carrier_uint {
     return (static_cast<carrier_uint>(
                 cache >> (64 - num_significand_bits<float>() - 2 - beta)) +
             1) /
@@ -345,7 +350,7 @@ template <> struct cache_accessor<double> {
   using carrier_uint = float_info<double>::carrier_uint;
   using cache_entry_type = uint128_fallback;
 
-  static uint128_fallback get_cached_power(int k) noexcept {
+  static auto get_cached_power(int k) noexcept -> uint128_fallback {
     FMT_ASSERT(k >= float_info<double>::min_k && k <= float_info<double>::max_k,
                "k is out of range");
 
@@ -1069,19 +1074,22 @@ template <> struct cache_accessor<double> {
     bool is_integer;
   };
 
-  static compute_mul_result compute_mul(
-      carrier_uint u, const cache_entry_type& cache) noexcept {
+  static auto compute_mul(carrier_uint u,
+                          const cache_entry_type& cache) noexcept
+      -> compute_mul_result {
     auto r = umul192_upper128(u, cache);
     return {r.high(), r.low() == 0};
   }
 
-  static uint32_t compute_delta(cache_entry_type const& cache,
-                                int beta) noexcept {
+  static auto compute_delta(cache_entry_type const& cache, int beta) noexcept
+      -> uint32_t {
     return static_cast<uint32_t>(cache.high() >> (64 - 1 - beta));
   }
 
-  static compute_mul_parity_result compute_mul_parity(
-      carrier_uint two_f, const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_mul_parity(carrier_uint two_f,
+                                 const cache_entry_type& cache,
+                                 int beta) noexcept
+      -> compute_mul_parity_result {
     FMT_ASSERT(beta >= 1, "");
     FMT_ASSERT(beta < 64, "");
 
@@ -1090,35 +1098,35 @@ template <> struct cache_accessor<double> {
             ((r.high() << beta) | (r.low() >> (64 - beta))) == 0};
   }
 
-  static carrier_uint compute_left_endpoint_for_shorter_interval_case(
-      const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_left_endpoint_for_shorter_interval_case(
+      const cache_entry_type& cache, int beta) noexcept -> carrier_uint {
     return (cache.high() -
             (cache.high() >> (num_significand_bits<double>() + 2))) >>
            (64 - num_significand_bits<double>() - 1 - beta);
   }
 
-  static carrier_uint compute_right_endpoint_for_shorter_interval_case(
-      const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_right_endpoint_for_shorter_interval_case(
+      const cache_entry_type& cache, int beta) noexcept -> carrier_uint {
     return (cache.high() +
             (cache.high() >> (num_significand_bits<double>() + 1))) >>
            (64 - num_significand_bits<double>() - 1 - beta);
   }
 
-  static carrier_uint compute_round_up_for_shorter_interval_case(
-      const cache_entry_type& cache, int beta) noexcept {
+  static auto compute_round_up_for_shorter_interval_case(
+      const cache_entry_type& cache, int beta) noexcept -> carrier_uint {
     return ((cache.high() >> (64 - num_significand_bits<double>() - 2 - beta)) +
             1) /
            2;
   }
 };
 
-FMT_FUNC uint128_fallback get_cached_power(int k) noexcept {
+FMT_FUNC auto get_cached_power(int k) noexcept -> uint128_fallback {
   return cache_accessor<double>::get_cached_power(k);
 }
 
 // Various integer checks
 template <typename T>
-bool is_left_endpoint_integer_shorter_interval(int exponent) noexcept {
+auto is_left_endpoint_integer_shorter_interval(int exponent) noexcept -> bool {
   const int case_shorter_interval_left_endpoint_lower_threshold = 2;
   const int case_shorter_interval_left_endpoint_upper_threshold = 3;
   return exponent >= case_shorter_interval_left_endpoint_lower_threshold &&
@@ -1232,7 +1240,7 @@ FMT_INLINE decimal_fp<T> shorter_interval_case(int exponent) noexcept {
   return ret_value;
 }
 
-template <typename T> decimal_fp<T> to_decimal(T x) noexcept {
+template <typename T> auto to_decimal(T x) noexcept -> decimal_fp<T> {
   // Step 1: integer promotion & Schubfach multiplier calculation.
 
   using carrier_uint = typename float_info<T>::carrier_uint;
@@ -1415,7 +1423,7 @@ FMT_FUNC void report_system_error(int error_code,
   report_error(format_system_error, error_code, message);
 }
 
-FMT_FUNC std::string vformat(string_view fmt, format_args args) {
+FMT_FUNC auto vformat(string_view fmt, format_args args) -> std::string {
   // Don't optimize the "{}" case to keep the binary size small and because it
   // can be better optimized in fmt::format anyway.
   auto buffer = memory_buffer();
@@ -1425,7 +1433,7 @@ FMT_FUNC std::string vformat(string_view fmt, format_args args) {
 
 namespace detail {
 #if !defined(_WIN32) || defined(FMT_WINDOWS_NO_WCHAR)
-FMT_FUNC bool write_console(int, string_view) { return false; }
+FMT_FUNC auto write_console(int, string_view) -> bool { return false; }
 #else
 using dword = conditional_t<sizeof(long) == 4, unsigned long, unsigned>;
 extern "C" __declspec(dllimport) int __stdcall WriteConsoleW(  //
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 7e1e6926..1ae0039e 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -377,8 +377,8 @@ class uint128_fallback {
   constexpr uint128_fallback(uint64_t hi, uint64_t lo) : lo_(lo), hi_(hi) {}
   constexpr uint128_fallback(uint64_t value = 0) : lo_(value), hi_(0) {}
 
-  constexpr uint64_t high() const noexcept { return hi_; }
-  constexpr uint64_t low() const noexcept { return lo_; }
+  constexpr auto high() const noexcept -> uint64_t { return hi_; }
+  constexpr auto low() const noexcept -> uint64_t { return lo_; }
 
   template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
   constexpr explicit operator T() const {
@@ -454,7 +454,7 @@ class uint128_fallback {
     hi_ &= n.hi_;
   }
 
-  FMT_CONSTEXPR20 uint128_fallback& operator+=(uint64_t n) noexcept {
+  FMT_CONSTEXPR20 auto operator+=(uint64_t n) noexcept -> uint128_fallback& {
     if (is_constant_evaluated()) {
       lo_ += n;
       hi_ += (lo_ < n ? 1 : 0);
@@ -744,7 +744,7 @@ inline auto compute_width(basic_string_view<Char> s) -> size_t {
 }
 
 // Computes approximate display width of a UTF-8 string.
-FMT_CONSTEXPR inline size_t compute_width(string_view s) {
+FMT_CONSTEXPR inline auto compute_width(string_view s) -> size_t {
   size_t num_code_points = 0;
   // It is not a lambda for compatibility with C++14.
   struct count_code_points {
@@ -1042,7 +1042,7 @@ struct is_contiguous<basic_memory_buffer<T, SIZE, Allocator>> : std::true_type {
 
 FMT_END_EXPORT
 namespace detail {
-FMT_API bool write_console(int fd, string_view text);
+FMT_API auto write_console(int fd, string_view text) -> bool;
 FMT_API void print(std::FILE*, string_view);
 }  // namespace detail
 
@@ -1167,7 +1167,7 @@ using uint64_or_128_t = conditional_t<num_bits<T>() <= 64, uint64_t, uint128_t>;
       (factor) * 100000000, (factor) * 1000000000
 
 // Converts value in the range [0, 100) to a string.
-constexpr const char* digits2(size_t value) {
+constexpr auto digits2(size_t value) -> const char* {
   // GCC generates slightly better code when value is pointer-size.
   return &"0001020304050607080910111213141516171819"
          "2021222324252627282930313233343536373839"
@@ -1177,7 +1177,7 @@ constexpr const char* digits2(size_t value) {
 }
 
 // Sign is a template parameter to workaround a bug in gcc 4.8.
-template <typename Char, typename Sign> constexpr Char sign(Sign s) {
+template <typename Char, typename Sign> constexpr auto sign(Sign s) -> Char {
 #if !FMT_GCC_VERSION || FMT_GCC_VERSION >= 604
   static_assert(std::is_same<Sign, sign_t>::value, "");
 #endif
@@ -1438,22 +1438,23 @@ template <typename WChar, typename Buffer = memory_buffer> class to_utf8 {
                                                       : "invalid utf32"));
   }
   operator string_view() const { return string_view(&buffer_[0], size()); }
-  size_t size() const { return buffer_.size() - 1; }
-  const char* c_str() const { return &buffer_[0]; }
-  std::string str() const { return std::string(&buffer_[0], size()); }
+  auto size() const -> size_t { return buffer_.size() - 1; }
+  auto c_str() const -> const char* { return &buffer_[0]; }
+  auto str() const -> std::string { return std::string(&buffer_[0], size()); }
 
   // Performs conversion returning a bool instead of throwing exception on
   // conversion error. This method may still throw in case of memory allocation
   // error.
-  bool convert(basic_string_view<WChar> s,
-               to_utf8_error_policy policy = to_utf8_error_policy::abort) {
+  auto convert(basic_string_view<WChar> s,
+               to_utf8_error_policy policy = to_utf8_error_policy::abort)
+      -> bool {
     if (!convert(buffer_, s, policy)) return false;
     buffer_.push_back(0);
     return true;
   }
-  static bool convert(
-      Buffer& buf, basic_string_view<WChar> s,
-      to_utf8_error_policy policy = to_utf8_error_policy::abort) {
+  static auto convert(Buffer& buf, basic_string_view<WChar> s,
+                      to_utf8_error_policy policy = to_utf8_error_policy::abort)
+      -> bool {
     for (auto p = s.begin(); p != s.end(); ++p) {
       uint32_t c = static_cast<uint32_t>(*p);
       if (sizeof(WChar) == 2 && c >= 0xd800 && c <= 0xdfff) {
@@ -1489,7 +1490,7 @@ template <typename WChar, typename Buffer = memory_buffer> class to_utf8 {
 };
 
 // Computes 128-bit result of multiplication of two 64-bit unsigned integers.
-inline uint128_fallback umul128(uint64_t x, uint64_t y) noexcept {
+inline auto umul128(uint64_t x, uint64_t y) noexcept -> uint128_fallback {
 #if FMT_USE_INT128
   auto p = static_cast<uint128_opt>(x) * static_cast<uint128_opt>(y);
   return {static_cast<uint64_t>(p >> 64), static_cast<uint64_t>(p)};
@@ -1520,19 +1521,19 @@ inline uint128_fallback umul128(uint64_t x, uint64_t y) noexcept {
 namespace dragonbox {
 // Computes floor(log10(pow(2, e))) for e in [-2620, 2620] using the method from
 // https://fmt.dev/papers/Dragonbox.pdf#page=28, section 6.1.
-inline int floor_log10_pow2(int e) noexcept {
+inline auto floor_log10_pow2(int e) noexcept -> int {
   FMT_ASSERT(e <= 2620 && e >= -2620, "too large exponent");
   static_assert((-1 >> 1) == -1, "right shift is not arithmetic");
   return (e * 315653) >> 20;
 }
 
-inline int floor_log2_pow10(int e) noexcept {
+inline auto floor_log2_pow10(int e) noexcept -> int {
   FMT_ASSERT(e <= 1233 && e >= -1233, "too large exponent");
   return (e * 1741647) >> 19;
 }
 
 // Computes upper 64 bits of multiplication of two 64-bit unsigned integers.
-inline uint64_t umul128_upper64(uint64_t x, uint64_t y) noexcept {
+inline auto umul128_upper64(uint64_t x, uint64_t y) noexcept -> uint64_t {
 #if FMT_USE_INT128
   auto p = static_cast<uint128_opt>(x) * static_cast<uint128_opt>(y);
   return static_cast<uint64_t>(p >> 64);
@@ -1545,14 +1546,14 @@ inline uint64_t umul128_upper64(uint64_t x, uint64_t y) noexcept {
 
 // Computes upper 128 bits of multiplication of a 64-bit unsigned integer and a
 // 128-bit unsigned integer.
-inline uint128_fallback umul192_upper128(uint64_t x,
-                                         uint128_fallback y) noexcept {
+inline auto umul192_upper128(uint64_t x, uint128_fallback y) noexcept
+    -> uint128_fallback {
   uint128_fallback r = umul128(x, y.high());
   r += umul128_upper64(x, y.low());
   return r;
 }
 
-FMT_API uint128_fallback get_cached_power(int k) noexcept;
+FMT_API auto get_cached_power(int k) noexcept -> uint128_fallback;
 
 // Type-specific information that Dragonbox uses.
 template <typename T, typename Enable = void> struct float_info;
@@ -1606,14 +1607,14 @@ template <typename T> FMT_API auto to_decimal(T x) noexcept -> decimal_fp<T>;
 }  // namespace dragonbox
 
 // Returns true iff Float has the implicit bit which is not stored.
-template <typename Float> constexpr bool has_implicit_bit() {
+template <typename Float> constexpr auto has_implicit_bit() -> bool {
   // An 80-bit FP number has a 64-bit significand an no implicit bit.
   return std::numeric_limits<Float>::digits != 64;
 }
 
 // Returns the number of significand bits stored in Float. The implicit bit is
 // not counted since it is not stored.
-template <typename Float> constexpr int num_significand_bits() {
+template <typename Float> constexpr auto num_significand_bits() -> int {
   // std::numeric_limits may not support __float128.
   return is_float128<Float>() ? 112
                               : (std::numeric_limits<Float>::digits -
@@ -1706,7 +1707,7 @@ using fp = basic_fp<unsigned long long>;
 
 // Normalizes the value converted from double and multiplied by (1 << SHIFT).
 template <int SHIFT = 0, typename F>
-FMT_CONSTEXPR basic_fp<F> normalize(basic_fp<F> value) {
+FMT_CONSTEXPR auto normalize(basic_fp<F> value) -> basic_fp<F> {
   // Handle subnormals.
   const auto implicit_bit = F(1) << num_significand_bits<double>();
   const auto shifted_implicit_bit = implicit_bit << SHIFT;
@@ -1723,7 +1724,7 @@ FMT_CONSTEXPR basic_fp<F> normalize(basic_fp<F> value) {
 }
 
 // Computes lhs * rhs / pow(2, 64) rounded to nearest with half-up tie breaking.
-FMT_CONSTEXPR inline uint64_t multiply(uint64_t lhs, uint64_t rhs) {
+FMT_CONSTEXPR inline auto multiply(uint64_t lhs, uint64_t rhs) -> uint64_t {
 #if FMT_USE_INT128
   auto product = static_cast<__uint128_t>(lhs) * rhs;
   auto f = static_cast<uint64_t>(product >> 64);
@@ -1740,7 +1741,7 @@ FMT_CONSTEXPR inline uint64_t multiply(uint64_t lhs, uint64_t rhs) {
 #endif
 }
 
-FMT_CONSTEXPR inline fp operator*(fp x, fp y) {
+FMT_CONSTEXPR inline auto operator*(fp x, fp y) -> fp {
   return {multiply(x.f, y.f), x.e + y.e + 64};
 }
 
@@ -2057,10 +2058,10 @@ template <typename Char> class digit_grouping {
     std::string::const_iterator group;
     int pos;
   };
-  next_state initial_state() const { return {grouping_.begin(), 0}; }
+  auto initial_state() const -> next_state { return {grouping_.begin(), 0}; }
 
   // Returns the next digit group separator position.
-  int next(next_state& state) const {
+  auto next(next_state& state) const -> int {
     if (thousands_sep_.empty()) return max_value<int>();
     if (state.group == grouping_.end()) return state.pos += grouping_.back();
     if (*state.group <= 0 || *state.group == max_value<char>())
@@ -2079,9 +2080,9 @@ template <typename Char> class digit_grouping {
   digit_grouping(std::string grouping, std::basic_string<Char> sep)
       : grouping_(std::move(grouping)), thousands_sep_(std::move(sep)) {}
 
-  bool has_separator() const { return !thousands_sep_.empty(); }
+  auto has_separator() const -> bool { return !thousands_sep_.empty(); }
 
-  int count_separators(int num_digits) const {
+  auto count_separators(int num_digits) const -> int {
     int count = 0;
     auto state = initial_state();
     while (num_digits > next(state)) ++count;
@@ -2090,7 +2091,7 @@ template <typename Char> class digit_grouping {
 
   // Applies grouping to digits and write the output to out.
   template <typename Out, typename C>
-  Out apply(Out out, basic_string_view<C> digits) const {
+  auto apply(Out out, basic_string_view<C> digits) const -> Out {
     auto num_digits = static_cast<int>(digits.size());
     auto separators = basic_memory_buffer<int>();
     separators.push_back(0);
@@ -2331,25 +2332,25 @@ class counting_iterator {
 
   FMT_CONSTEXPR counting_iterator() : count_(0) {}
 
-  FMT_CONSTEXPR size_t count() const { return count_; }
+  FMT_CONSTEXPR auto count() const -> size_t { return count_; }
 
-  FMT_CONSTEXPR counting_iterator& operator++() {
+  FMT_CONSTEXPR auto operator++() -> counting_iterator& {
     ++count_;
     return *this;
   }
-  FMT_CONSTEXPR counting_iterator operator++(int) {
+  FMT_CONSTEXPR auto operator++(int) -> counting_iterator {
     auto it = *this;
     ++*this;
     return it;
   }
 
-  FMT_CONSTEXPR friend counting_iterator operator+(counting_iterator it,
-                                                   difference_type n) {
+  FMT_CONSTEXPR friend auto operator+(counting_iterator it, difference_type n)
+      -> counting_iterator {
     it.count_ += static_cast<size_t>(n);
     return it;
   }
 
-  FMT_CONSTEXPR value_type operator*() const { return {}; }
+  FMT_CONSTEXPR auto operator*() const -> value_type { return {}; }
 };
 
 template <typename Char, typename OutputIt>
@@ -2750,12 +2751,12 @@ template <typename Char> class fallback_digit_grouping {
  public:
   constexpr fallback_digit_grouping(locale_ref, bool) {}
 
-  constexpr bool has_separator() const { return false; }
+  constexpr auto has_separator() const -> bool { return false; }
 
-  constexpr int count_separators(int) const { return 0; }
+  constexpr auto count_separators(int) const -> int { return 0; }
 
   template <typename Out, typename C>
-  constexpr Out apply(Out out, basic_string_view<C>) const {
+  constexpr auto apply(Out out, basic_string_view<C>) const -> Out {
     return out;
   }
 };
@@ -2774,7 +2775,7 @@ FMT_CONSTEXPR20 auto write_float(OutputIt out, const DecimalFP& f,
   }
 }
 
-template <typename T> constexpr bool isnan(T value) {
+template <typename T> constexpr auto isnan(T value) -> bool {
   return !(value >= value);  // std::isnan doesn't support __float128.
 }
 
@@ -2787,14 +2788,14 @@ struct has_isfinite<T, enable_if_t<sizeof(std::isfinite(T())) != 0>>
 
 template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value&&
                                         has_isfinite<T>::value)>
-FMT_CONSTEXPR20 bool isfinite(T value) {
+FMT_CONSTEXPR20 auto isfinite(T value) -> bool {
   constexpr T inf = T(std::numeric_limits<double>::infinity());
   if (is_constant_evaluated())
     return !detail::isnan(value) && value < inf && value > -inf;
   return std::isfinite(value);
 }
 template <typename T, FMT_ENABLE_IF(!has_isfinite<T>::value)>
-FMT_CONSTEXPR bool isfinite(T value) {
+FMT_CONSTEXPR auto isfinite(T value) -> bool {
   T inf = T(std::numeric_limits<double>::infinity());
   // std::isfinite doesn't support __float128.
   return !detail::isnan(value) && value < inf && value > -inf;
@@ -2831,10 +2832,10 @@ class bigint {
   basic_memory_buffer<bigit, bigits_capacity> bigits_;
   int exp_;
 
-  FMT_CONSTEXPR20 bigit operator[](int index) const {
+  FMT_CONSTEXPR20 auto operator[](int index) const -> bigit {
     return bigits_[to_unsigned(index)];
   }
-  FMT_CONSTEXPR20 bigit& operator[](int index) {
+  FMT_CONSTEXPR20 auto operator[](int index) -> bigit& {
     return bigits_[to_unsigned(index)];
   }
 
@@ -2930,11 +2931,11 @@ class bigint {
     assign(uint64_or_128_t<Int>(n));
   }
 
-  FMT_CONSTEXPR20 int num_bigits() const {
+  FMT_CONSTEXPR20 auto num_bigits() const -> int {
     return static_cast<int>(bigits_.size()) + exp_;
   }
 
-  FMT_NOINLINE FMT_CONSTEXPR20 bigint& operator<<=(int shift) {
+  FMT_NOINLINE FMT_CONSTEXPR20 auto operator<<=(int shift) -> bigint& {
     FMT_ASSERT(shift >= 0, "");
     exp_ += shift / bigit_bits;
     shift %= bigit_bits;
@@ -2949,13 +2950,15 @@ class bigint {
     return *this;
   }
 
-  template <typename Int> FMT_CONSTEXPR20 bigint& operator*=(Int value) {
+  template <typename Int>
+  FMT_CONSTEXPR20 auto operator*=(Int value) -> bigint& {
     FMT_ASSERT(value > 0, "");
     multiply(uint32_or_64_or_128_t<Int>(value));
     return *this;
   }
 
-  friend FMT_CONSTEXPR20 int compare(const bigint& lhs, const bigint& rhs) {
+  friend FMT_CONSTEXPR20 auto compare(const bigint& lhs, const bigint& rhs)
+      -> int {
     int num_lhs_bigits = lhs.num_bigits(), num_rhs_bigits = rhs.num_bigits();
     if (num_lhs_bigits != num_rhs_bigits)
       return num_lhs_bigits > num_rhs_bigits ? 1 : -1;
@@ -2972,8 +2975,9 @@ class bigint {
   }
 
   // Returns compare(lhs1 + lhs2, rhs).
-  friend FMT_CONSTEXPR20 int add_compare(const bigint& lhs1, const bigint& lhs2,
-                                         const bigint& rhs) {
+  friend FMT_CONSTEXPR20 auto add_compare(const bigint& lhs1,
+                                          const bigint& lhs2, const bigint& rhs)
+      -> int {
     auto minimum = [](int a, int b) { return a < b ? a : b; };
     auto maximum = [](int a, int b) { return a > b ? a : b; };
     int max_lhs_bigits = maximum(lhs1.num_bigits(), lhs2.num_bigits());
@@ -3060,7 +3064,7 @@ class bigint {
 
   // Divides this bignum by divisor, assigning the remainder to this and
   // returning the quotient.
-  FMT_CONSTEXPR20 int divmod_assign(const bigint& divisor) {
+  FMT_CONSTEXPR20 auto divmod_assign(const bigint& divisor) -> int {
     FMT_ASSERT(this != &divisor, "");
     if (compare(*this, divisor) < 0) return 0;
     FMT_ASSERT(divisor.bigits_[divisor.bigits_.size() - 1u] != 0, "");
@@ -3303,7 +3307,7 @@ FMT_CONSTEXPR20 void format_hexfloat(Float value, int precision,
   format_hexfloat(static_cast<double>(value), precision, specs, buf);
 }
 
-constexpr uint32_t fractional_part_rounding_thresholds(int index) {
+constexpr auto fractional_part_rounding_thresholds(int index) -> uint32_t {
   // For checking rounding thresholds.
   // The kth entry is chosen to be the smallest integer such that the
   // upper 32-bits of 10^(k+1) times it is strictly bigger than 5 * 10^k.
diff --git a/include/fmt/os.h b/include/fmt/os.h
index 462ac44d..c81955d7 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -117,7 +117,7 @@ template <typename Char> class basic_cstring_view {
   basic_cstring_view(const std::basic_string<Char>& s) : data_(s.c_str()) {}
 
   /** Returns the pointer to a C string. */
-  const Char* c_str() const { return data_; }
+  auto c_str() const -> const Char* { return data_; }
 };
 
 using cstring_view = basic_cstring_view<char>;
@@ -172,7 +172,7 @@ std::system_error windows_error(int error_code, string_view message,
 // Can be used to report errors from destructors.
 FMT_API void report_windows_error(int error_code, const char* message) noexcept;
 #else
-inline const std::error_category& system_category() noexcept {
+inline auto system_category() noexcept -> const std::error_category& {
   return std::system_category();
 }
 #endif  // _WIN32
@@ -209,7 +209,7 @@ class buffered_file {
     other.file_ = nullptr;
   }
 
-  buffered_file& operator=(buffered_file&& other) {
+  auto operator=(buffered_file&& other) -> buffered_file& {
     close();
     file_ = other.file_;
     other.file_ = nullptr;
@@ -223,9 +223,9 @@ class buffered_file {
   FMT_API void close();
 
   // Returns the pointer to a FILE object representing this file.
-  FILE* get() const noexcept { return file_; }
+  auto get() const noexcept -> FILE* { return file_; }
 
-  FMT_API int descriptor() const;
+  FMT_API auto descriptor() const -> int;
 
   void vprint(string_view format_str, format_args args) {
     fmt::vprint(file_, format_str, args);
@@ -275,7 +275,7 @@ class FMT_API file {
   file(file&& other) noexcept : fd_(other.fd_) { other.fd_ = -1; }
 
   // Move assignment is not noexcept because close may throw.
-  file& operator=(file&& other) {
+  auto operator=(file&& other) -> file& {
     close();
     fd_ = other.fd_;
     other.fd_ = -1;
@@ -286,24 +286,24 @@ class FMT_API file {
   ~file() noexcept;
 
   // Returns the file descriptor.
-  int descriptor() const noexcept { return fd_; }
+  auto descriptor() const noexcept -> int { return fd_; }
 
   // Closes the file.
   void close();
 
   // Returns the file size. The size has signed type for consistency with
   // stat::st_size.
-  long long size() const;
+  auto size() const -> long long;
 
   // Attempts to read count bytes from the file into the specified buffer.
-  size_t read(void* buffer, size_t count);
+  auto read(void* buffer, size_t count) -> size_t;
 
   // Attempts to write count bytes from the specified buffer to the file.
-  size_t write(const void* buffer, size_t count);
+  auto write(const void* buffer, size_t count) -> size_t;
 
   // Duplicates a file descriptor with the dup function and returns
   // the duplicate as a file object.
-  static file dup(int fd);
+  static auto dup(int fd) -> file;
 
   // Makes fd be the copy of this file descriptor, closing fd first if
   // necessary.
@@ -319,7 +319,7 @@ class FMT_API file {
 
   // Creates a buffered_file object associated with this file and detaches
   // this file object from the file.
-  buffered_file fdopen(const char* mode);
+  auto fdopen(const char* mode) -> buffered_file;
 
 #  if defined(_WIN32) && !defined(__MINGW32__)
   // Opens a file and constructs a file object representing this file by
@@ -329,14 +329,14 @@ class FMT_API file {
 };
 
 // Returns the memory page size.
-long getpagesize();
+auto getpagesize() -> long;
 
 namespace detail {
 
 struct buffer_size {
   buffer_size() = default;
   size_t value = 0;
-  buffer_size operator=(size_t val) const {
+  auto operator=(size_t val) const -> buffer_size {
     auto bs = buffer_size();
     bs.value = val;
     return bs;
@@ -413,7 +413,7 @@ class FMT_API ostream {
   void flush() { buffer_.flush(); }
 
   template <typename... T>
-  friend ostream output_file(cstring_view path, T... params);
+  friend auto output_file(cstring_view path, T... params) -> ostream;
 
   void close() { buffer_.close(); }
 
@@ -443,7 +443,7 @@ class FMT_API ostream {
   \endrst
  */
 template <typename... T>
-inline ostream output_file(cstring_view path, T... params) {
+inline auto output_file(cstring_view path, T... params) -> ostream {
   return {path, detail::ostream_params(params...)};
 }
 #endif  // FMT_USE_FCNTL
diff --git a/include/fmt/ostream.h b/include/fmt/ostream.h
index 3086191a..3eb62143 100644
--- a/include/fmt/ostream.h
+++ b/include/fmt/ostream.h
@@ -40,7 +40,8 @@ template class file_access<file_access_tag, std::filebuf,
 auto get_file(std::filebuf&) -> FILE*;
 #endif
 
-inline bool write_ostream_unicode(std::ostream& os, fmt::string_view data) {
+inline auto write_ostream_unicode(std::ostream& os, fmt::string_view data)
+    -> bool {
   FILE* f = nullptr;
 #if FMT_MSC_VERSION
   if (auto* buf = dynamic_cast<std::filebuf*>(os.rdbuf()))
@@ -69,8 +70,8 @@ inline bool write_ostream_unicode(std::ostream& os, fmt::string_view data) {
 #endif
   return false;
 }
-inline bool write_ostream_unicode(std::wostream&,
-                                  fmt::basic_string_view<wchar_t>) {
+inline auto write_ostream_unicode(std::wostream&,
+                                  fmt::basic_string_view<wchar_t>) -> bool {
   return false;
 }
 
diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index c0b51aee..d4501529 100644
--- a/include/fmt/ranges.h
+++ b/include/fmt/ranges.h
@@ -183,7 +183,7 @@ template <size_t N> using make_index_sequence = std::make_index_sequence<N>;
 template <typename T, T... N> struct integer_sequence {
   using value_type = T;
 
-  static FMT_CONSTEXPR size_t size() { return sizeof...(N); }
+  static FMT_CONSTEXPR auto size() -> size_t { return sizeof...(N); }
 };
 
 template <size_t... N> using index_sequence = integer_sequence<size_t, N...>;
@@ -207,15 +207,15 @@ class is_tuple_formattable_ {
 };
 template <typename T, typename C> class is_tuple_formattable_<T, C, true> {
   template <std::size_t... Is>
-  static std::true_type check2(index_sequence<Is...>,
-                               integer_sequence<bool, (Is == Is)...>);
-  static std::false_type check2(...);
+  static auto check2(index_sequence<Is...>,
+                     integer_sequence<bool, (Is == Is)...>) -> std::true_type;
+  static auto check2(...) -> std::false_type;
   template <std::size_t... Is>
-  static decltype(check2(
+  static auto check(index_sequence<Is...>) -> decltype(check2(
       index_sequence<Is...>{},
-      integer_sequence<
-          bool, (is_formattable<typename std::tuple_element<Is, T>::type,
-                                C>::value)...>{})) check(index_sequence<Is...>);
+      integer_sequence<bool,
+                       (is_formattable<typename std::tuple_element<Is, T>::type,
+                                       C>::value)...>{}));
 
  public:
   static constexpr const bool value =
diff --git a/include/fmt/std.h b/include/fmt/std.h
index 5bafcefb..a9a9dc33 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -176,7 +176,7 @@ struct formatter<std::bitset<N>, Char> : nested_formatter<string_view> {
     const std::bitset<N>& bs;
 
     template <typename OutputIt>
-    FMT_CONSTEXPR OutputIt operator()(OutputIt out) {
+    FMT_CONSTEXPR auto operator()(OutputIt out) -> OutputIt {
       for (auto pos = N; pos > 0; --pos) {
         out = detail::write<Char>(out, bs[pos - 1] ? Char('1') : Char('0'));
       }
diff --git a/include/fmt/xchar.h b/include/fmt/xchar.h
index 9a7aa4d7..f609c5c4 100644
--- a/include/fmt/xchar.h
+++ b/include/fmt/xchar.h
@@ -63,14 +63,15 @@ template <> struct is_char<char16_t> : std::true_type {};
 template <> struct is_char<char32_t> : std::true_type {};
 
 template <typename... T>
-constexpr format_arg_store<wformat_context, T...> make_wformat_args(
-    const T&... args) {
+constexpr auto make_wformat_args(const T&... args)
+    -> format_arg_store<wformat_context, T...> {
   return {args...};
 }
 
 inline namespace literals {
 #if FMT_USE_USER_DEFINED_LITERALS && !FMT_USE_NONTYPE_TEMPLATE_ARGS
-constexpr detail::udl_arg<wchar_t> operator""_a(const wchar_t* s, size_t) {
+constexpr auto operator""_a(const wchar_t* s, size_t)
+    -> detail::udl_arg<wchar_t> {
   return {s};
 }
 #endif