Can't run clang-tidy on 12.0

[olavsr]

Hi!

I'm trying to upgrade fmt from 11.2.0 to 12.0 in our codebase. This made clang-tidy fail on files that include fmt/std.h, not due to warnings as those are disabled for "external" code, it actually just fails to run. I get the following output (anonymized a bit as this is from a corporate codebase):

FAILED: /workspaces/env/libs/.../file.cpp.o 
/usr/bin/cmake -E __run_co_compile --launcher=ccache --tidy="clang-tidy-19;-warnings-as-errors=-*;--format-style=file;--extra-arg-before=--driver-mode=g++;--export-fixes=/workspaces/env/libs/.../file.cpp.o.yaml" --source=/workspaces/env/libs/.../file.cpp -- /usr/bin/g++-10 ... -isystem /workspaces/env/extern/fmt/fmt/include -isystem /workspaces/env/extern/spdlog/spdlog/include ... -march=x86-64-v3 -mtune=skylake -O3 -DNDEBUG -g -std=c++2a -fPIC -Werror -Wall -Wextra -Wpedantic -Wformat=2 -Wfloat-equal -Wnull-dereference -Wshadow -Wconversion -Wsign-conversion -Wcast-align -Woverloaded-virtual -Wmisleading-indentation -Wnon-virtual-dtor -Wold-style-cast -Wlogical-op -Wtrampolines -Wduplicated-cond -Wduplicated-branches -Wuseless-cast -pthread -MD -MT /workspaces/env/libs/.../file.cpp.o -MF /workspaces/env/libs/.../file.cpp.od -o /workspaces/env/libs/.../file.cpp.o -c /workspaces/env/libs/.../file.cpp
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:2295:45: error: implicit instantiation of undefined template 'fmt::detail::type_is_unformattable_for<std::filesystem::path, char>' [clang-diagnostic-error]
 2295 |     type_is_unformattable_for<T, char_type> _;
      |                                             ^
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:2268:44: note: in instantiation of function template specialization 'fmt::detail::value<fmt::context>::value<std::filesystem::path, 0>' requested here
 2268 |   FMT_CONSTEXPR20 FMT_INLINE value(T& x) : value(x, custom_tag()) {}
      |                                            ^
/workspaces/env/extern/fmt/fmt/include/fmt/format.h:4349:40: note: in instantiation of function template specialization 'fmt::detail::value<fmt::context>::value<const std::filesystem::path, 0>' requested here
 4349 |   return vformat(fmt.str, vargs<T...>{{args...}});
      |                                        ^
/workspaces/env/extern/fmt/fmt/include/fmt/std.h:263:17: note: in instantiation of function template specialization 'fmt::format<const std::filesystem::path &>' requested here
  263 |     return fmt::format(FMT_STRING("{}"), base);
      |                 ^
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:2135:45: note: template is declared here
 2135 | template <typename T, typename Char> struct type_is_unformattable_for;
      |                                             ^
/workspaces/env/extern/fmt/fmt/include/fmt/std.h:269:35: error: call to consteval function 'fmt::fstring<const std::filesystem::path &>::fstring<5UL>' is not a constant expression [clang-diagnostic-error]
  269 |     return fmt::format(FMT_STRING("{:g}"), base);
      |                                   ^
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:1757:5: note: non-constexpr function 'report_error' cannot be used in a constant expression
 1757 |     report_error(message);
      |     ^
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:1641:12: note: in call to 'handler.on_error(&"unknown format specifier"[0])'
 1641 |     return handler.on_error("unknown format specifier"), end;
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:1654:19: note: in call to 'parse_replacement_field<char, fmt::detail::format_string_checker<char, 1, 0, false> &>(&"{:g}"[2], &"{:g}"[4], checker(s, arg_pack()))'
 1654 |       begin = p = parse_replacement_field(p - 1, end, handler);
      |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:2744:28: note: in call to 'parse_format_string<char, fmt::detail::format_string_checker<char, 1, 0, false>>({&"{:g}"[0], 4}, checker(s, arg_pack()))'
 2744 |     if (FMT_USE_CONSTEVAL) parse_format_string<char>(s, checker(s, arg_pack()));
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/workspaces/env/extern/fmt/fmt/include/fmt/std.h:269:35: note: in call to 'fstring<5UL>("{:g}")'
  269 |     return fmt::format(FMT_STRING("{:g}"), base);
      |                                   ^
/workspaces/env/extern/fmt/fmt/include/fmt/format.h:4251:39: note: expanded from macro 'FMT_STRING'
 4251 | #define FMT_STRING(s) FMT_STRING_IMPL(s, fmt::detail::compile_string)
      |                                       ^
/workspaces/env/extern/fmt/fmt/include/fmt/format.h:4223:36: note: expanded from macro 'FMT_STRING_IMPL'
 4223 | #  define FMT_STRING_IMPL(s, base) s
      |                                    ^
/workspaces/env/extern/fmt/fmt/include/fmt/base.h:656:27: note: declared here
  656 | FMT_NORETURN FMT_API void report_error(const char* message);
      |                           ^
13692 warnings and 2 errors generated.
Error while processing /workspaces/env/libs/.../file.cpp.
Suppressed 13705 warnings (13692 in non-user code, 13 NOLINT).
Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well.
Found compiler error(s).
ninja: build stopped: subcommand failed.

We use clang-tidy-19, but I tried with clang-tidy-21 as well which fails in the same way. We invoke clang-tidy through CMake, there could to be some interaction there as I cannot recreate the issue when running clang-tidy-19 by itself. The changes in 619b3a5 introduced these issues for us. Reverting that commit, or just setting FMT_CLANG_ANALYZER=0 for both cases in fmt/format.h fixes the issue. Setting FMT_CPP_LIB_FILESYSTEM=0 also works as a workaround. Is something broken here or are we just doing something wrong?

[vitaut]

Repro: https://www.godbolt.org/z/Ede5oTch8

[vitaut]

Fixed in 17be91c, thanks for reporting.