Add std::tm formatter, fix spdlog::stopwatch formatter, conditionally use fmt::runtime in test_errors

3 files changed, 105 insertions, 4 deletions

diff --git a/include/spdlog/fmt/chrono.h b/include/spdlog/fmt/chrono.h
index 83fad2ff..17013bc1 100644
--- a/include/spdlog/fmt/chrono.h
+++ b/include/spdlog/fmt/chrono.h
@@ -4,11 +4,93 @@
 //
 
 #pragma once
+
+#if defined(SPDLOG_USE_STD_FORMAT)
+// Add a formatter for std::tm, since std::format only supports std::chrono
+// taken from fmtlib
+#include <cassert>
+#include <ctime>
+#include <format>
+#include <string>
+#include <string_view>
+#include <type_traits>
+#include <spdlog/common.h>
+
+namespace spdlog::details
+{
+    inline size_t strftime(char *str, size_t count, const char *format, const std::tm *time)
+    {
+        // Assign to a pointer to suppress GCCs -Wformat-nonliteral
+        // First assign the nullptr to suppress -Wsuggest-attribute=format
+        std::size_t (*strftime)(char*, std::size_t, const char*, const std::tm*) = nullptr;
+        strftime = std::strftime;
+        return strftime(str, count, format, time);
+    }
+
+    inline size_t strftime(wchar_t *str, size_t count, const wchar_t *format, const std::tm *time)
+    {
+        // See above
+        std::size_t (*wcsftime)(wchar_t*, std::size_t, const wchar_t*, const std::tm*) = nullptr;
+        wcsftime = std::wcsftime;
+        return wcsftime(str, count, format, time);
+    }
+
+    // Casts a nonnegative integer to unsigned.
+    template <typename Int>
+    SPDLOG_CONSTEXPR auto to_unsigned(Int value) -> typename std::make_unsigned<Int>::type
+    {
+        assert(value >= 0, "negative value");
+        return static_cast<typename std::make_unsigned<Int>::type>(value);
+    }
+}
+
+template <typename Char>
+struct std::formatter<std::tm, Char>
+{
+    template <typename ParseContext>
+    SPDLOG_CONSTEXPR_FUNC auto parse(ParseContext &ctx) -> decltype(ctx.begin())
+    {
+        auto it = ctx.begin();
+        if (it != ctx.end() && *it == ':') ++it;
+        auto end = it;
+        while (end != ctx.end() && *end != '}') ++end;
+        specs = {it, spdlog::details::to_unsigned(end - it)};
+        return end;
+    }
+
+    template <typename FormatContext>
+    auto format(const std::tm &tm, FormatContext &ctx) const -> decltype(ctx.out()) {
+        basic_string<Char> tm_format;
+        tm_format.append(specs);
+        // By appending an extra space we can distinguish an empty result that
+        // indicates insufficient buffer size from a guaranteed non-empty result
+        // https://github.com/fmtlib/fmt/issues/2238
+        tm_format.push_back(' ');
+
+        const size_t MIN_SIZE = 10;
+        basic_string<Char> buf;
+        buf.resize(MIN_SIZE);
+        for (;;)
+        {
+            size_t count = spdlog::details::strftime(buf.data(), buf.size(), tm_format.c_str(), &tm);
+            if (count != 0)
+            {
+                buf.resize(count);
+                break;
+            }
+            buf.resize(buf.size() * 2);
+        }
+        // Remove the extra space.
+        return std::copy(buf.begin(), buf.end() - 1, ctx.out());
+    }
+
+    basic_string_view<Char> specs;
+};
+
+#else
 //
 // include bundled or external copy of fmtlib's chrono support
 //
-
-#if !defined(SPDLOG_USE_STD_FORMAT)
 #    if !defined(SPDLOG_FMT_EXTERNAL)
 #        ifdef SPDLOG_HEADER_ONLY
 #            ifndef FMT_HEADER_ONLY
diff --git a/include/spdlog/stopwatch.h b/include/spdlog/stopwatch.h
index bb976b19..52b4b6ad 100644
--- a/include/spdlog/stopwatch.h
+++ b/include/spdlog/stopwatch.h
@@ -48,7 +48,14 @@ public:
 } // namespace spdlog
 
 // Support for fmt formatting  (e.g. "{:012.9}" or just "{}")
-namespace fmt {
+namespace
+#ifdef SPDLOG_USE_STD_FORMAT
+    std
+#else
+    fmt
+#endif
+{
+
 template<>
 struct formatter<spdlog::stopwatch> : formatter<double>
 {
@@ -58,4 +65,4 @@ struct formatter<spdlog::stopwatch> : formatter<double>
         return formatter<double>::format(sw.elapsed().count(), ctx);
     }
 };
-} // namespace fmt
+} // namespace fmt/std
diff --git a/tests/test_errors.cpp b/tests/test_errors.cpp
index 41441d0d..c7aef812 100644
--- a/tests/test_errors.cpp
+++ b/tests/test_errors.cpp
@@ -29,7 +29,11 @@ TEST_CASE("default_error_handler", "[errors]]")
 
     auto logger = spdlog::create<spdlog::sinks::basic_file_sink_mt>("test-error", filename, true);
     logger->set_pattern("%v");
+#ifdef SPDLOG_USE_STD_FORMAT
+    logger->info("Test message {} {}", 1);
+#else
     logger->info(fmt::runtime("Test message {} {}"), 1);
+#endif
     logger->info("Test message {}", 2);
     logger->flush();
 
@@ -49,7 +53,11 @@ TEST_CASE("custom_error_handler", "[errors]]")
     logger->set_error_handler([=](const std::string &) { throw custom_ex(); });
     logger->info("Good message #1");
 
+#ifdef SPDLOG_USE_STD_FORMAT
+    REQUIRE_THROWS_AS(logger->info("Bad format msg {} {}", "xxx"), custom_ex);
+#else
     REQUIRE_THROWS_AS(logger->info(fmt::runtime("Bad format msg {} {}"), "xxx"), custom_ex);
+#endif
     logger->info("Good message #2");
     require_message_count(SIMPLE_LOG, 2);
 }
@@ -88,7 +96,11 @@ TEST_CASE("async_error_handler", "[errors]]")
             ofs << err_msg;
         });
         logger->info("Good message #1");
+#ifdef SPDLOG_USE_STD_FORMAT
+        logger->info("Bad format msg {} {}", "xxx");
+#else
         logger->info(fmt::runtime("Bad format msg {} {}"), "xxx");
+#endif
         logger->info("Good message #2");
         spdlog::drop("logger"); // force logger to drain the queue and shutdown
     }