Optimized chrono formatting (#2500, #2537, #2541, #2544, #2550, #2551, #2576, #2577, #2586, #2591, #2594, #2602, #2617, #2628, #2633, #2670, #2671).

Processing of some specifiers such as %z and %Y is now up to 10-20 times faster, for example on GCC 11 with libstdc++:

----------------------------------------------------------------------------
Benchmark                                  Before             After
----------------------------------------------------------------------------
FMTFormatter_z                             261 ns             26.3 ns
FMTFormatterCompile_z                      246 ns             11.6 ns
FMTFormatter_Y                             263 ns             26.1 ns
FMTFormatterCompile_Y                      244 ns             10.5 ns
----------------------------------------------------------------------------

Thanks @phprus (Vladislav Shchapov) and @toughengineer (Pavel Novikov).

Implemented subsecond formatting for chrono durations (#2623). For example (godbolt):

#include <fmt/chrono.h>

int main() {
  fmt::print("{:%S}", std::chrono::milliseconds(1234));
}

prints "01.234".

Thanks @matrackif.

Fixed handling of precision 0 when formatting chrono durations (#2587, #2588). Thanks @lukester1975.

Fixed an overflow on invalid inputs in the tm formatter (#2564). Thanks @phprus (Vladislav Shchapov).

Added fmt::group_digits that formats integers with a non-localized digit separator (comma) for groups of three digits. For example (godbolt):

#include <fmt/format.h>

int main() {
  fmt::print("{} dollars", fmt::group_digits(1000000));
}

prints "1,000,000 dollars".

Added support for faint, conceal, reverse and blink text styles (#2394):

https://user-images.githubusercontent.com/576385/147710227-c68f5317-f8fa-42c3-9123-7c4ba3c398cb.mp4

Thanks @benit8 (Benoît Lormeau) and @data-man (Dmitry Atamanov).

Added experimental support for compile-time floating point formatting (#2426, #2470). It is currently limited to the header-only mode. Thanks @alexezeder (Alexey Ochapov).

Added UDL-based named argument support to compile-time format string checks (#2640, #2649). For example (godbolt):

#include <fmt/format.h>

int main() {
  using namespace fmt::literals;
  fmt::print("{answer:s}", "answer"_a=42);
}

gives a compile-time error on compilers with C++20 consteval and non-type template parameter support (gcc 10+) because s is not a valid format specifier for an integer.

Thanks @alexezeder (Alexey Ochapov).

Implemented escaping of string range elements. For example (godbolt):

#include <fmt/ranges.h>
#include <vector>

int main() {
  fmt::print("{}", std::vector<std::string>{"\naan"});
}

is now printed as:

["\naan"]

instead of:

["
aan"]

Switched to JSON-like representation of maps and sets for consistency with Python's str.format. For example (godbolt):

#include <fmt/ranges.h>
#include <map>

int main() {
  fmt::print("{}", std::map<std::string, int>{{"answer", 42}});
}

is now printed as:

{"answer": 42}

Extended fmt::join to support C++20-only ranges (#2549). Thanks @BRevzin (Barry Revzin).

Optimized handling of non-const-iterable ranges and implemented initial support for non-const-formattable types.

Disabled implicit conversions of scoped enums to integers that was accidentally introduced in earlier versions (#1841).

Deprecated implicit conversion of [const] signed char* and [const] unsigned char* to C strings.

Deprecated _format, a legacy UDL-based format API (#2646). Thanks @alexezeder (Alexey Ochapov).

Marked format, formatted_size and to_string as [[nodiscard]] (#2612). @0x8000-0000 (Florin Iucha).

Added missing diagnostic when trying to format function and member pointers as well as objects convertible to pointers which is explicitly disallowed (#2598, #2609, #2610). Thanks @AlexGuteniev (Alex Guteniev).

Optimized writing to a contiguous buffer with format_to_n (#2489). Thanks @Roman-Koshelev.

Optimized writing to non-char buffers (#2477). Thanks @Roman-Koshelev.

Decimal point is now localized when using the L specifier.

Improved floating point formatter implementation (#2498, #2499). Thanks @Roman-Koshelev.

Fixed handling of very large precision in fixed format (#2616).

Made a table of cached powers used in FP formatting static (#2509). Thanks @jk-jeon (Junekey Jeon).

Resolved a lookup ambiguity with C++20 format-related functions due to ADL (#2639, #2641). Thanks @mkurdej (Marek Kurdej).

Removed unnecessary inline namespace qualification (#2642, #2643). Thanks @mkurdej (Marek Kurdej).

Implemented argument forwarding in format_to_n (#2462, #2463). Thanks @owent (WenTao Ou).

Fixed handling of implicit conversions in fmt::to_string and format string compilation (#2565).

Changed the default access mode of files created by fmt::output_file to -rw-r--r-- for consistency with fopen (#2530).

Make fmt::ostream::flush public (#2435).

Improved C++14/17 attribute detection (#2615). Thanks @AlexGuteniev (Alex Guteniev).

Improved consteval detection for MSVC (#2559). Thanks @DanielaE (Daniela Engert).

Improved documentation (#2406, #2446, #2493, #2513, #2515, #2522, #2562, #2575, #2606, #2620, #2676). Thanks @sobolevn (Nikita Sobolev), @UnePierre (Max FERGER), @zhsj, @phprus (Vladislav Shchapov), @ericcurtin (Eric Curtin), @Lounarok.

Improved fuzzers and added a fuzzer for chrono timepoint formatting (#2461, #2469). @pauldreik (Paul Dreik),

Added the FMT_SYSTEM_HEADERS CMake option setting which marks {fmt}'s headers as system. It can be used to suppress warnings (#2644, #2651). Thanks @alexezeder (Alexey Ochapov).

Added the Bazel build system support (#2505, #2516). Thanks @Vertexwahn.

Improved build configuration and tests (#2437, #2558, #2648, #2650, #2663, #2677). Thanks @DanielaE (Daniela Engert), @alexezeder (Alexey Ochapov), @phprus (Vladislav Shchapov).

Fixed various warnings and compilation issues (#2353, #2356, #2399, #2408, #2414, #2427, #2432, #2442, #2434, #2439, #2447, #2450, #2455, #2465, #2472, #2474, #2476, #2478, #2479, #2481, #2482, #2483, #2490, #2491, #2510, #2518, #2528, #2529, #2539, #2540, #2545, #2555, #2557, #2570, #2573, #2582, #2605, #2611, #2647, #2627, #2630, #2635, #2638, #2653, #2654, #2661, #2664, #2684). Thanks @DanielaE (Daniela Engert), @mwinterb, @cdacamar (Cameron DaCamara), @TrebledJ (Johnathan), @bodomartin (brm), @cquammen (Cory Quammen), @white238 (Chris White), @mmarkeloff (Max), @palacaze (Pierre-Antoine Lacaze), @jcelerier (Jean-Michaël Celerier), @mborn-adi (Mathias Born), @BrukerJWD (Jonathan W), @spyridon97 (Spiros Tsalikis), @phprus (Vladislav Shchapov), @oliverlee (Oliver Lee), @joshessman-llnl (Josh Essman), @akohlmey (Axel Kohlmeyer), @timkalu, @olupton (Olli Lupton), @Acretock, @alexezeder (Alexey Ochapov), @andrewcorrigan (Andrew Corrigan), @lucpelletier, @HazardyKnusperkeks (Björn Schäpers).