12.1.0

• Optimized buffer::append, resulting in up to ~16% improvement on spdlog benchmarks (#4541). Thanks @fyrsta7.

• Worked around an ABI incompatibility in std::locale_ref between clang and gcc (#4573).

• Made std::variant and std::expected formatters work with format_as (#4574, #4575). Thanks @phprus.

• Made fmt::join<string_view> work with C++ modules (#4379, #4577). Thanks @Arghnews.

• Exported fmt::is_compiled_string and operator""_cf from the module (#4544). Thanks @CrackedMatter.

• Fixed a compatibility issue with C++ modules in clang (#4548). Thanks @tsarn.

• Added support for cv-qualified types to the std::optional formatter (#4561, #4562). Thanks @OleksandrKvl.

• Added demangling support (used in exception and std::type_info formatters) for libc++ and clang-cl (#4542, #4560, #4568, #4571). Thanks @FatihBAKIR and @rohitsutreja.

• Switched to global malloc/free to enable allocator customization (#4569, #4570). Thanks @rohitsutreja.

• Made the FMT_USE_CONSTEVAL macro configurable by users (#4546). Thanks @SnapperTT.

• Fixed compilation with locales disabled in the header-only mode (#4550).

• Fixed compilation with clang 21 and -std=c++20 (#4552).

• Fixed a dynamic linking issue with clang-cl (#4576, #4584). Thanks @FatihBAKIR.

• Fixed a warning suppression leakage on gcc (#4588). Thanks @ZedThree.

• Made more internal color APIs constexpr (#4581). Thanks @ishani.

• Fixed compatibility with clang as a host compiler for NVCC (#4564). Thanks @valgur.

• Fixed various warnings and lint issues (#4565, #4572, #4557). Thanks @LiangHuDream and @teruyamato0731.

• Improved documentation (#4549, #4551, #4566, #4567, #4578,). Thanks @teruyamato0731, @petersteneteg and @zimmerman-dev.