fmt

This occurs because fmt::detail::is_printable was generated from Unicode 13.0 data. Code points added in Unicode 14.0–17.0, such as 🫠 U+1FAE0 and CJK Extensions H/I/J, are incorrectly classified as unassigned (Cn) and therefore escaped. Update {fmt} to a release or commit containing the Update is_printable to Unicode 17.0 fix. If maintaining a fork, regenerate the table from Unicode 17.0.0 UnicodeData.txt by running python3 support/printable.py—updating the script’s Unicode version/data URL if it is pinned—and replace the generated is_printable code, then rebuild. Afterward, fmt::print("{:?}\n", "🫠") outputs "🫠" instead of "\U0001fae0".

This is a known MSVC false positive triggered by fmt 12.2.0's range formatter. Patch the formatter() constructor in include/fmt/ranges.h so set_brackets() is in an else branch:

FMT_CONSTEXPR formatter() {
  if FMT_CONSTEXPR20 (range_format_kind<R, Char>::value != range_format::set)
    return;
  else
    range_formatter_.set_brackets(detail::string_literal<Char, '{'>{},
                                  detail::string_literal<Char, '}'>{});
}

Then rebuild. As a temporary workaround, you can disable the warning for the third-party header with #pragma warning(disable: 4702) or compile with /wd4702, but applying the patch or upgrading to a fmt release containing the fix is preferred.

Fetch tags in all submodules before updating them:

git submodule foreach --recursive 'git fetch --tags'
git submodule update --recursive

This is needed when the submodule points to a tag whose commit is not reachable from any configured branch. A permanent fix is for the maintainer to tag the release on a maintained branch or create a separate release branch.

This was an fmt bug: with locale support disabled, {:L} was ignored for integers, used a hard-coded comma fallback for floating-point values, and some chrono formatters consulted std::locale(), which is the global locale. Update to an fmt release containing the fixes for issue #4941, or apply the upstream changes "Use classic locale grouping without locale support" and "Don't require std::locale in chrono.h when FMT_USE_LOCALE is 0". After the fix, L is accepted but uses classic/C-locale semantics: fmt::format("{:L}", 1234567) remains 1234567, and fmt::format("{:L}", 1234.5) returns 1234.5 without comma grouping. Define the macro before including fmt, for example with C++: #define FMT_USE_LOCALE 0 before #include <fmt/...>, or CMake: target_compile_definitions(my_target PRIVATE FMT_USE_LOCALE=0), then rebuild. On affected versions, remove L from format strings as a workaround. If you need locale-specific numbers or chrono names, build with FMT_USE_LOCALE=1 and pass the desired std::locale explicitly to fmt::format.

The type is both a range because it inherits std::array and has a format_as overload, so {fmt}'s range formatter and format_as support are ambiguous. Clang crashes instead of reporting the ambiguity. Resolve it by providing an explicit fmt::formatter specialization for your type:

#include <fmt/format.h>

template <>
struct fmt::formatter<Sha256Hash> : fmt::formatter<std::string>
{
    auto format(const Sha256Hash& h, fmt::format_context& ctx) const
    {
        return fmt::formatter<std::string>::format(format_as(h), ctx);
    }
};

Alternatively, remove format_as if you want the default range formatting, or use composition instead of publicly inheriting std::array so the type is not recognized as a range. The Clang segfault itself is a compiler bug in Clang 15 through 20, but the ambiguity is the underlying source issue.