FMT_EXCEPTIONS not being set to 0 when SPDLOG_NO_EXCEPTIONS is OFF

[rafaelBauer]

The fmt exceptions are still enable in MSVC even after SPDLOG_NO_EXCEPTIONS has been set to OFF. https://github.com/gabime/spdlog/blob/069a2e8fc947f63855d770fdc3c3eb427f19988f/CMakeLists.txt#L258-L260

A possible fix would be to set the target compiler flags to disable exception such as:

And change line 258 to 260 to:

if(SPDLOG_NO_EXCEPTIONS)
     if(NOT SPDLOG_FMT_EXTERNAL OR NOT SPDLOG_FMT_EXTERNAL_HO)
         target_compile_definitions(spdlog PUBLIC FMT_EXCEPTIONS=0)
     endif()
     if(NOT MSVC) 
          target_compile_options(spdlog PRIVATE -fno-exceptions)
     else()
          target_compile_options(spdlog PRIVATE /EHsc)
     endif()
endif()

[gabime]

what does /EHsc do?

[tt4g]

The definitions of the FMT_TRY and FMT_NORETURN macros branch off at the FMT_EXCEPTIONS macro.

https://github.com/fmtlib/fmt/blob/bce8d4ed087a0560492426f9f5be2713804daded/include/fmt/format.h#L131-L137

https://github.com/fmtlib/fmt/blob/bce8d4ed087a0560492426f9f5be2713804daded/include/fmt/core.h#L141-L147

If an unbundled fmt library was built with FMT_EXCEPTIONS=1, wouldn't that break application binary compatibility?

[rafaelBauer]

what does /EHsc do?

The /EH is to define the exception handling in MSVC. the options s and c are:

• s: Enables standard C++ stack unwinding. Catches only standard C++ exceptions when you use catch(...) syntax.
• c: When used with /EHs, the compiler assumes that functions declared as extern "C" never throw a C++ exception. Took those from https://learn.microsoft.com/en-us/cpp/build/reference/eh-exception-handling-model?view=msvc-170

The definitions of the FMT_TRY and FMT_NORETURN macros branch off at the FMT_EXCEPTIONS macro.

https://github.com/fmtlib/fmt/blob/bce8d4ed087a0560492426f9f5be2713804daded/include/fmt/format.h#L131-L137

https://github.com/fmtlib/fmt/blob/bce8d4ed087a0560492426f9f5be2713804daded/include/fmt/core.h#L141-L147

If an unbundled fmt library was built with FMT_EXCEPTIONS=1, wouldn't that break application binary compatibility?

I am not sure about it, but wouldn't the check if(NOT SPDLOG_FMT_EXTERNAL OR NOT SPDLOG_FMT_EXTERNAL_HO) before setting target_compile_definitions(spdlog PUBLIC FMT_EXCEPTIONS=0) prevent that?

Also as far as I understand, the fmt library, when set to be external, is statically linked to SPDLOG, no? As per those lines: https://github.com/gabime/spdlog/blob/069a2e8fc947f63855d770fdc3c3eb427f19988f/CMakeLists.txt#L217-L223 https://github.com/gabime/spdlog/blob/069a2e8fc947f63855d770fdc3c3eb427f19988f/CMakeLists.txt#L157-L170

[tt4g]

I am not sure about it, but wouldn't the check if(NOT SPDLOG_FMT_EXTERNAL OR NOT SPDLOG_FMT_EXTERNAL_HO) before setting target_compile_definitions(spdlog PUBLIC FMT_EXCEPTIONS=0) prevent that?

Probably, yes.

[gabime]

Fixed in d1eb68154f2a60c7d59e99d1504e6c6ac03fedb4

Thanks @rafaelBauer .