Support C++20 std::format as an alternative to fmtlib

CMakeLists.txt

@@ -80,6 +80,7 @@ option(SPDLOG_BUILD_WARNINGS "Enable compiler warnings" OFF)
 
 # install options
 option(SPDLOG_INSTALL "Generate the install target" ${SPDLOG_MASTER_PROJECT})
+option(SPDLOG_USE_STD_FORMAT "Use std::format instead of fmt library. No compile-time format string checking." OFF)
 option(SPDLOG_FMT_EXTERNAL "Use external fmt library instead of bundled" OFF)
 option(SPDLOG_FMT_EXTERNAL_HO "Use external fmt header-only library instead of bundled" OFF)
 option(SPDLOG_NO_EXCEPTIONS "Compile with -fno-exceptions. Call abort() on any spdlog exceptions" OFF)
@@ -88,6 +89,14 @@ if(SPDLOG_FMT_EXTERNAL AND SPDLOG_FMT_EXTERNAL_HO)
     message(FATAL_ERROR "SPDLOG_FMT_EXTERNAL and SPDLOG_FMT_EXTERNAL_HO are mutually exclusive")
 endif()
 
+if(SPDLOG_USE_STD_FORMAT AND SPDLOG_FMT_EXTERNAL_HO)
+    message(FATAL_ERROR "SPDLOG_USE_STD_FORMAT and SPDLOG_FMT_EXTERNAL_HO are mutually exclusive")
+endif()
+
+if(SPDLOG_USE_STD_FORMAT AND SPDLOG_FMT_EXTERNAL)
+    message(FATAL_ERROR "SPDLOG_USE_STD_FORMAT and SPDLOG_FMT_EXTERNAL are mutually exclusive")
+endif()
+
 # misc tweakme options
 if(WIN32)
     option(SPDLOG_WCHAR_SUPPORT "Support wchar api" OFF)
@@ -130,7 +139,7 @@ message(STATUS "Build type: " ${CMAKE_BUILD_TYPE})
 # ---------------------------------------------------------------------------------------
 set(SPDLOG_SRCS src/spdlog.cpp src/stdout_sinks.cpp src/color_sinks.cpp src/file_sinks.cpp src/async.cpp src/cfg.cpp)
 
-if(NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
+if(NOT SPDLOG_USE_STD_FORMAT AND NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
     list(APPEND SPDLOG_SRCS src/fmt.cpp)
 endif()
 
@@ -145,7 +154,7 @@ if(SPDLOG_BUILD_SHARED OR BUILD_SHARED_LIBS)
         target_compile_options(spdlog PUBLIC $<$<AND:$<CXX_COMPILER_ID:MSVC>,$<NOT:$<COMPILE_LANGUAGE:CUDA>>>:/wd4251
                                              /wd4275>)
     endif()
-    if(NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
+    if(NOT SPDLOG_USE_STD_FORMAT AND NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
         target_compile_definitions(spdlog PRIVATE FMT_EXPORT PUBLIC FMT_SHARED)
     endif()
 else()
@@ -280,7 +289,7 @@ if(SPDLOG_INSTALL)
         ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
         RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
 
-    if(NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
+    if(NOT SPDLOG_USE_STD_FORMAT AND NOT SPDLOG_FMT_EXTERNAL AND NOT SPDLOG_FMT_EXTERNAL_HO)
         install(DIRECTORY include/${PROJECT_NAME}/fmt/bundled/
                 DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}/fmt/bundled/")
     endif()

appveyor.yml

@@ -8,55 +8,72 @@ environment:
       WCHAR: 'OFF'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 14 2015"'
       BUILD_TYPE: Release
       BUILD_SHARED: 'OFF'
       WCHAR: 'ON'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 14 2015 Win64"'
       BUILD_TYPE: Debug
       BUILD_SHARED: 'OFF'
       WCHAR: 'ON'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 14 2015 Win64"'
       BUILD_TYPE: Release
       BUILD_SHARED: 'OFF'
       WCHAR: 'ON'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 15 2017 Win64"'
       BUILD_TYPE: Debug
       BUILD_SHARED: 'OFF'
       WCHAR: 'ON'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 15 2017 Win64"'
       BUILD_TYPE: Release
       BUILD_SHARED: 'OFF'
       WCHAR: 'OFF'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 15 2017 Win64"'
       BUILD_TYPE: Release
       BUILD_SHARED: 'ON'
       WCHAR: 'OFF'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'ON'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 15 2017 Win64"'
       BUILD_TYPE: Release
       BUILD_SHARED: 'ON'
       WCHAR: 'ON'
       WCHAR_FILES: 'ON'
       BUILD_EXAMPLE: 'OFF'
+      USE_STD_FORMAT: 'OFF'
     - GENERATOR: '"Visual Studio 16 2019" -A x64'
       BUILD_TYPE: Release
       BUILD_SHARED: 'ON'
       WCHAR: 'OFF'
       WCHAR_FILES: 'OFF'
       BUILD_EXAMPLE: 'OFF'
+      USE_STD_FORMAT: 'OFF'
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+    - GENERATOR: '"Visual Studio 16 2022" -A x64'
+      BUILD_TYPE: Release
+      BUILD_SHARED: 'ON'
+      WCHAR: 'OFF'
+      WCHAR_FILES: 'OFF'
+      BUILD_EXAMPLE: 'OFF'
+      USE_STD_FORMAT: 'ON'
+      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2022
 build_script:
   - cmd: >-
       set
@@ -67,7 +84,7 @@ build_script:
 
       set PATH=%PATH%;C:\Program Files\Git\usr\bin
 
-      cmake -G %GENERATOR% -D CMAKE_BUILD_TYPE=%BUILD_TYPE% -D BUILD_SHARED_LIBS=%BUILD_SHARED% -D SPDLOG_WCHAR_SUPPORT=%WCHAR% -D SPDLOG_WCHAR_FILENAMES=%WCHAR_FILES% -D SPDLOG_BUILD_EXAMPLE=%BUILD_EXAMPLE% -D SPDLOG_BUILD_EXAMPLE_HO=%BUILD_EXAMPLE% -D SPDLOG_BUILD_TESTS=ON -D SPDLOG_BUILD_TESTS_HO=OFF -D SPDLOG_BUILD_WARNINGS=ON ..
+      cmake -G %GENERATOR% -D CMAKE_BUILD_TYPE=%BUILD_TYPE% -D BUILD_SHARED_LIBS=%BUILD_SHARED% -D SPDLOG_WCHAR_SUPPORT=%WCHAR% -D SPDLOG_WCHAR_FILENAMES=%WCHAR_FILES% -D SPDLOG_BUILD_EXAMPLE=%BUILD_EXAMPLE% -D SPDLOG_BUILD_EXAMPLE_HO=%BUILD_EXAMPLE% -D SPDLOG_BUILD_TESTS=ON -D SPDLOG_BUILD_TESTS_HO=OFF -D SPDLOG_BUILD_WARNINGS=ON -D SPDLOG_USE_STD_FORMAT=%USE_STD_FORMAT% ..
 
       cmake --build . --config %BUILD_TYPE%
 

bench/async_bench.cpp

@@ -10,7 +10,9 @@
 #include "spdlog/async.h"
 #include "spdlog/sinks/basic_file_sink.h"
 
-#ifdef SPDLOG_FMT_EXTERNAL
+#if defined(SPDLOG_USE_STD_FORMAT)
+#    include <format>
+#elif defined(SPDLOG_FMT_EXTERNAL)
 #    include <fmt/format.h>
 #else
 #    include "spdlog/fmt/bundled/format.h"

bench/bench.cpp

@@ -12,7 +12,9 @@
 #include "spdlog/sinks/null_sink.h"
 #include "spdlog/sinks/rotating_file_sink.h"
 
-#ifdef SPDLOG_FMT_EXTERNAL
+#if defined(SPDLOG_USE_STD_FORMAT)
+#    include <format>
+#elif defined(SPDLOG_FMT_EXTERNAL)
 #    include <fmt/locale.h>
 #else
 #    include "spdlog/fmt/bundled/format.h"
@@ -38,7 +40,7 @@ static const int max_threads = 1000;
 void bench_threaded_logging(size_t threads, int iters)
 {
     spdlog::info("**************************************************************");
-    spdlog::info(fmt::format(std::locale("en_US.UTF-8"), "Multi threaded: {:L} threads, {:L} messages", threads, iters));
+    spdlog::info(spdlog::fmt_lib::format(std::locale("en_US.UTF-8"), "Multi threaded: {:L} threads, {:L} messages", threads, iters));
     spdlog::info("**************************************************************");
 
     auto basic_mt = spdlog::basic_logger_mt("basic_mt", "logs/basic_mt.log", true);
@@ -74,7 +76,7 @@ void bench_threaded_logging(size_t threads, int iters)
 void bench_single_threaded(int iters)
 {
     spdlog::info("**************************************************************");
-    spdlog::info(fmt::format(std::locale("en_US.UTF-8"), "Single threaded: {} messages", iters));
+    spdlog::info(spdlog::fmt_lib::format(std::locale("en_US.UTF-8"), "Single threaded: {} messages", iters));
     spdlog::info("**************************************************************");
 
     auto basic_st = spdlog::basic_logger_st("basic_st", "logs/basic_st.log", true);
@@ -128,7 +130,7 @@ int main(int argc, char *argv[])
 
         if (threads > max_threads)
         {
-            throw std::runtime_error(fmt::format("Number of threads exceeds maximum({})", max_threads));
+            throw std::runtime_error(spdlog::fmt_lib::format("Number of threads exceeds maximum({})", max_threads));
         }
 
         bench_single_threaded(iters);
@@ -159,7 +161,7 @@ void bench(int howmany, std::shared_ptr<spdlog::logger> log)
     auto delta_d = duration_cast<duration<double>>(delta).count();
 
     spdlog::info(
-        fmt::format(std::locale("en_US.UTF-8"), "{:<30} Elapsed: {:0.2f} secs {:>16L}/sec", log->name(), delta_d, int(howmany / delta_d)));
+        spdlog::fmt_lib::format(std::locale("en_US.UTF-8"), "{:<30} Elapsed: {:0.2f} secs {:>16L}/sec", log->name(), delta_d, int(howmany / delta_d)));
     spdlog::drop(log->name());
 }
 
@@ -190,7 +192,7 @@ void bench_mt(int howmany, std::shared_ptr<spdlog::logger> log, size_t thread_co
     auto delta = high_resolution_clock::now() - start;
     auto delta_d = duration_cast<duration<double>>(delta).count();
     spdlog::info(
-        fmt::format(std::locale("en_US.UTF-8"), "{:<30} Elapsed: {:0.2f} secs {:>16L}/sec", log->name(), delta_d, int(howmany / delta_d)));
+        spdlog::fmt_lib::format(std::locale("en_US.UTF-8"), "{:<30} Elapsed: {:0.2f} secs {:>16L}/sec", log->name(), delta_d, int(howmany / delta_d)));
     spdlog::drop(log->name());
 }
 

include/spdlog/common-inl.h

@@ -55,9 +55,13 @@ SPDLOG_INLINE spdlog_ex::spdlog_ex(std::string msg)
 
 SPDLOG_INLINE spdlog_ex::spdlog_ex(const std::string &msg, int last_errno)
 {
+#ifdef SPDLOG_USE_STD_FORMAT
+    msg_ = std::system_error(std::error_code(last_errno, std::generic_category()), msg).what();
+#else
     memory_buf_t outbuf;
     fmt::format_system_error(outbuf, last_errno, msg.c_str());
     msg_ = fmt::to_string(outbuf);
+#endif
 }
 
 SPDLOG_INLINE const char *spdlog_ex::what() const SPDLOG_NOEXCEPT

include/spdlog/common.h

@@ -16,6 +16,10 @@
 #include <functional>
 #include <cstdio>
 
+#ifdef SPDLOG_USE_STD_FORMAT
+#include <string_view>
+#endif
+
 #ifdef SPDLOG_COMPILED_LIB
 #    undef SPDLOG_HEADER_ONLY
 #    if defined(_WIN32) && defined(SPDLOG_SHARED_LIB)
@@ -36,14 +40,15 @@
 
 #include <spdlog/fmt/fmt.h>
 
-// backward compatibility with fmt versions older than 8
-#if FMT_VERSION >= 80000
-#    define SPDLOG_FMT_RUNTIME(format_string) fmt::runtime(format_string)
-#    if defined(SPDLOG_WCHAR_FILENAMES) || defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT)
-#        include <spdlog/fmt/xchar.h>
+#ifndef SPDLOG_USE_STD_FORMAT
+#    if FMT_VERSION >= 80000 // backward compatibility with fmt versions older than 8
+#        define SPDLOG_FMT_RUNTIME(format_string) fmt::runtime(format_string)
+#        if defined(SPDLOG_WCHAR_FILENAMES) || defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT)
+#            include <spdlog/fmt/xchar.h>
+#        endif
+#    else
+#        define SPDLOG_FMT_RUNTIME(format_string) format_string
 #    endif
-#else
-#    define SPDLOG_FMT_RUNTIME(format_string) format_string
 #endif
 
 // visual studio upto 2013 does not support noexcept nor constexpr
@@ -112,11 +117,39 @@ using log_clock = std::chrono::system_clock;
 using sink_ptr = std::shared_ptr<sinks::sink>;
 using sinks_init_list = std::initializer_list<sink_ptr>;
 using err_handler = std::function<void(const std::string &err_msg)>;
+#ifdef SPDLOG_USE_STD_FORMAT
+namespace fmt_lib = std;
+
+using string_view_t = std::string_view;
+using wstring_view_t = std::wstring_view;
+using memory_buf_t = std::string;
+using wmemory_buf_t = std::wstring;
+
+template<typename... Args>
+using format_string_t = std::string_view;
+
+template<typename... Args>
+using wformat_string_t = std::wstring_view;
+
+template<class T, class Char = char>
+struct is_convertible_to_basic_format_string
+    : std::integral_constant<bool,
+          std::is_convertible<T, std::basic_string_view<Char>>::value>
+{};
+#else
+namespace fmt_lib = fmt;
+
 using string_view_t = fmt::basic_string_view<char>;
 using wstring_view_t = fmt::basic_string_view<wchar_t>;
 using memory_buf_t = fmt::basic_memory_buffer<char, 250>;
 using wmemory_buf_t = fmt::basic_memory_buffer<wchar_t, 250>;
 
+template<typename... Args>
+using format_string_t = fmt::format_string<Args...>;
+
+template<typename... Args>
+using wformat_string_t = fmt::wformat_string<Args...>;
+
 template<class T>
 using remove_cvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
 
@@ -127,6 +160,7 @@ struct is_convertible_to_basic_format_string
     : std::integral_constant<bool,
           std::is_convertible<T, fmt::basic_string_view<Char>>::value || std::is_same<remove_cvref_t<T>, fmt::basic_runtime<Char>>::value>
 {};
+#endif
 
 #ifdef SPDLOG_WCHAR_TO_UTF8_SUPPORT
 #    ifndef _WIN32

include/spdlog/details/fmt_helper.h

@@ -8,6 +8,11 @@
 #include <spdlog/fmt/fmt.h>
 #include <spdlog/common.h>
 
+#ifdef SPDLOG_USE_STD_FORMAT
+#include <charconv>
+#include <limits>
+#endif
+
 // Some fmt helpers to efficiently format and pad ints and strings
 namespace spdlog {
 namespace details {
@@ -24,17 +29,63 @@ inline void append_string_view(spdlog::string_view_t view, memory_buf_t &dest)
     dest.append(buf_ptr, buf_ptr + view.size());
 }
 
+#ifdef SPDLOG_USE_STD_FORMAT
+template<typename T>
+inline void append_int(T n, memory_buf_t &dest)
+{
+    // Buffer should be large enough to hold all digits (digits10 + 1) and a sign
+    SPDLOG_CONSTEXPR auto BUF_SIZE = std::numeric_limits<T>::digits10 + 2;
+    char buf[BUF_SIZE];
+
+    auto [ptr, ec] = std::to_chars(buf, buf + BUF_SIZE, n, 10);
+    if (ec == std::errc())
+    {
+        dest.append(buf, ptr);
+    }
+    else
+    {
+        throw_spdlog_ex("Failed to format int", static_cast<int>(ec));
+    }
+}
+#else
 template<typename T>
 inline void append_int(T n, memory_buf_t &dest)
 {
     fmt::format_int i(n);
     dest.append(i.data(), i.data() + i.size());
 }
+#endif
+
+template<typename T>
+SPDLOG_CONSTEXPR unsigned int count_digits_fallback(T n)
+{
+    // taken from fmt.
+    unsigned int count = 1;
+    for (;;)
+    {
+        // Integer division is slow so do it for a group of four digits instead
+        // of for every digit. The idea comes from the talk by Alexandrescu
+        // "Three Optimization Tips for C++". See speed-test for a comparison.
+        if (n < 10)
+            return count;
+        if (n < 100)
+            return count + 1;
+        if (n < 1000)
+            return count + 2;
+        if (n < 10000)
+            return count + 3;
+        n /= 10000u;
+        count += 4;
+    }
+}
 
 template<typename T>
 inline unsigned int count_digits(T n)
 {
     using count_type = typename std::conditional<(sizeof(T) > sizeof(uint32_t)), uint64_t, uint32_t>::type;
+#ifdef SPDLOG_USE_STD_FORMAT
+    return count_digits_fallback(static_cast<count_type>(n));
+#else
     return static_cast<unsigned int>(fmt::
 // fmt 7.0.0 renamed the internal namespace to detail.
 // See: https://github.com/fmtlib/fmt/issues/1538
@@ -44,6 +95,7 @@ inline unsigned int count_digits(T n)
             detail
 #endif
         ::count_digits(static_cast<count_type>(n)));
+#endif
 }
 
 inline void pad2(int n, memory_buf_t &dest)
@@ -55,7 +107,7 @@ inline void pad2(int n, memory_buf_t &dest)
     }
     else // unlikely, but just in case, let fmt deal with it
     {
-        fmt::format_to(std::back_inserter(dest), SPDLOG_FMT_RUNTIME("{:02}"), n);
+        fmt_lib::format_to(std::back_inserter(dest), "{:02}", n);
     }
 }