Improved error reporting when trying to format an object of a non-formattable type:

fmt::format("{}", S());

now gives:

include/fmt/core.h:1015:5: error: static_assert failed due to requirement
'formattable' "Cannot format argument. To make type T formattable provide a
formatter<T> specialization:
https://fmt.dev/latest/api.html#formatting-user-defined-types"
    static_assert(
    ^
...
note: in instantiation of function template specialization
'fmt::v6::format<char [3], S, char>' requested here
  fmt::format("{}", S());
       ^

if S is not formattable.

Reduced library size by ~10%.

Always print decimal point if # is specified (#1476, #1498):

fmt::print("{:#.0f}", 42.0);

now prints 42.

Implemented the 'L' specifier for locale-specific numeric formatting to improve compatibility with std::format. The 'n' specifier is now deprecated and will be removed in the next major release.

Moved OS-specific APIs such as windows_error from fmt/format.h to fmt/os.h. You can define FMT_DEPRECATED_INCLUDE_OS to automatically include fmt/os.h from fmt/format.h for compatibility but this will be disabled in the next major release.

Added precision overflow detection in floating-point formatting.

Implemented detection of invalid use of fmt::arg.

Used type_identity to block unnecessary template argument deduction. Thanks Tim Song.

Improved UTF-8 handling (#1109):

fmt::print("┌{0:─^{2}}┐\n"
           "│{1: ^{2}}│\n"
           "└{0:─^{2}}┘\n", "", "Привет, мир!", 20);

now prints:

┌────────────────────┐
│    Привет, мир!    │
└────────────────────┘

on systems that support Unicode.

Added experimental dynamic argument storage (#1170, #1584):

fmt::dynamic_format_arg_store<fmt::format_context> store;
store.push_back("answer");
store.push_back(42);
fmt::vprint("The {} is {}.\n", store);

prints:

The answer is 42.

Thanks @vsolontsov-ll (Vladimir Solontsov).

Made fmt::join accept initializer_list (#1591). Thanks @Rapotkinnik (Nikolay Rapotkin).

Fixed handling of empty tuples (#1588).

Fixed handling of output iterators in format_to_n (#1506).

Fixed formatting of std::chrono::duration types to wide output (#1533). Thanks @zeffy (pilao).

Added const begin and end overload to buffers (#1553). Thanks @dominicpoeschko.

Added the ability to disable floating-point formatting via FMT_USE_FLOAT, FMT_USE_DOUBLE and FMT_USE_LONG_DOUBLE macros for extremely memory-constrained embedded system (#1590). Thanks @albaguirre (Alberto Aguirre).

Made FMT_STRING work with constexpr string_view (#1589). Thanks @scramsby (Scott Ramsby).

Implemented a minor optimization in the format string parser (#1560). Thanks @IkarusDeveloper.

Improved attribute detection (#1469, #1475, #1576). Thanks @federico-busato (Federico), @chronoxor (Ivan Shynkarenka), @refnum.

Improved documentation (#1481, #1523). Thanks @JackBoosY (Jack·Boos·Yu), @imba-tjd (谭九鼎).

Fixed symbol visibility on Linux when compiling with -fvisibility=hidden (#1535). Thanks @milianw (Milian Wolff).

Implemented various build configuration fixes and improvements (#1264, #1460, #1534, #1536, #1545, #1546, #1566, #1582, #1597, #1598). Thanks @ambitslix (Attila M. Szilagyi), @jwillikers (Jordan Williams), @stac47 (Laurent Stacul).

Fixed various warnings and compilation issues (#1433, #1461, #1470, #1480, #1485, #1492, #1493, #1504, #1505, #1512, #1515, #1516, #1518, #1519, #1520, #1521, #1522, #1524, #1530, #1531, #1532, #1539, #1547, #1548, #1554, #1567, #1568, #1569, #1571, #1573, #1575, #1581, #1583, #1586, #1587, #1594, #1596, #1604, #1606, #1607, #1609). Thanks @marti4d (Chris Martin), @iPherian, @parkertomatoes, @gsjaardema (Greg Sjaardema), @chronoxor (Ivan Shynkarenka), @DanielaE (Daniela Engert), @torsten48, @tohammer (Tobias Hammer), @lefticus (Jason Turner), @ryusakki (Haise), @adnsv (Alex Denisov), @fghzxm, @refnum, @pramodk (Pramod Kumbhar), @Spirrwell, @scramsby (Scott Ramsby).