8.0.0 fails to compile with Debian Jessie's GCC 4.9.2

[patlkli]

I just tried updating {fmt} from 7.1.3 to 8.0.0 and ran into an issue when building our project on Debian Jessie which sits on GCC 4.9.2.

{fmt} 8.0.0 fails to compile with the following errors:

[  1%] Building CXX object CMakeFiles/fmt.dir/src/format.cc.o
In file included from /fmt/include/fmt/format-inl.h:29:0,
                 from /fmt/src/format.cc:8:
/fmt/include/fmt/format.h: In instantiation of 'constexpr const char fmt::v7::detail::basic_data<>::digits [][2]':
/fmt/include/fmt/format.h:1066:22:   required from here
/fmt/include/fmt/format.h:862:39: error: initializer fails to determine size of 'fmt::v7::detail::basic_data<>::digits'
   FMT_API static constexpr const char digits[][2] = {
                                       ^
/fmt/include/fmt/format.h:862:39: error: array must be initialized with a brace-enclosed initializer
/fmt/include/fmt/format.h: In instantiation of 'constexpr const char fmt::v7::detail::basic_data<>::left_padding_shifts []':
/fmt/include/fmt/format.h:1283:47:   required from here
/fmt/include/fmt/format.h:885:39: error: initializer fails to determine size of 'fmt::v7::detail::basic_data<>::left_padding_shifts'
   FMT_API static constexpr const char left_padding_shifts[] = {31, 31, 0, 1, 0};
                                       ^
/fmt/include/fmt/format.h:885:39: error: array must be initialized with a brace-enclosed initializer
/fmt/include/fmt/format.h: In instantiation of 'constexpr const char fmt::v7::detail::basic_data<>::right_padding_shifts []':
/fmt/include/fmt/format.h:1284:47:   required from here
/fmt/include/fmt/format.h:886:39: error: initializer fails to determine size of 'fmt::v7::detail::basic_data<>::right_padding_shifts'
   FMT_API static constexpr const char right_padding_shifts[] = {0, 31, 0, 1, 0};
                                       ^
/fmt/include/fmt/format.h:886:39: error: array must be initialized with a brace-enclosed initializer
/fmt/include/fmt/format.h: In instantiation of 'constexpr const char fmt::v7::detail::basic_data<>::signs []':
/fmt/include/fmt/format.h:1594:47:   required from here
/fmt/include/fmt/format.h:882:39: error: initializer fails to determine size of 'fmt::v7::detail::basic_data<>::signs'
   FMT_API static constexpr const char signs[] = {0, '-', '+', ' '};
                                       ^
/fmt/include/fmt/format.h:882:39: error: array must be initialized with a brace-enclosed initializer

This is most likely caused by GCC bug #66921, which is fixed in GCC 4.9.4. This version however no longer got into Jessie.

Any chance this could be workarounded in {fmt}?

[vitaut]

If you happen to know a workaround, a PR would be welcome.