Package: libspdlog-dev Version: 1:1.12.0+ds-2 Hello, libspdlog currently links against libfmt 9 but Trixie moved on to libfmt 10 which is ABI incompatible. hilarity ensues :)
$ ldd /usr/lib/aarch64-linux-gnu/libspdlog.so linux-vdso.so.1 (0x0000ffff0bae8000) libfmt.so.9 => /lib/aarch64-linux-gnu/libfmt.so.9 (0x0000ffff0b9c0000) ... Repro: spdlog.cpp: #include <spdlog/spdlog.h> int main() { spdlog::error("Some error message with arg: {}", 1); } Build: $ clang++ spdlog.cpp -DSPDLOG_COMPILED_LIB=1 -lspdlog -lfmt /usr/bin/ld: warning: libfmt.so.9, needed by /lib/aarch64-linux-gnu/libspdlog.so, may conflict with libfmt.so.10 /usr/bin/ld: /tmp/spdlog-b8b221.o: in function `void spdlog::logger::log_<int>(spdlog::source_loc, spdlog::level::level_enum, fmt::v10::basic_string_view<char>, int&&)': spdlog.cpp:(.text._ZN6spdlog6logger4log_IJiEEEvNS_10source_locENS_5level10level_enumEN3fmt3v1017basic_string_viewIcEEDpOT_[_ZN6spdlog6logger4log_IJiEEEvNS_10source_locENS_5level10level_enumEN3fmt3v1017basic_string_viewIcEEDpOT_]+0x210): undefined reference to `spdlog::details::log_msg::log_msg(spdlog::source_loc, fmt::v10::basic_string_view<char>, spdlog::level::level_enum, fmt::v10::basic_string_view<char>)' clang: error: linker command failed with exit code 1 (use -v to see invocation) Kind regards, Jean-Michaël