Support CMake 3.10-3.20

[carstene1ns]

Analogous to EasyRPG/liblcf#422.

This shows a problem btw.: We are currently not compatible to libfmt version 5 (since StringView is in). Solved.

log with 5.2.1

2021-05-14T19:23:08.8410634Z [15/342] Building CXX object CMakeFiles/EasyRPG_Player.dir/src/autobattle.cpp.o
2021-05-14T19:23:08.8412921Z FAILED: CMakeFiles/EasyRPG_Player.dir/src/autobattle.cpp.o 
2021-05-14T19:23:08.8417399Z /usr/bin/c++  -DHAVE_FREETYPE=1 -DHAVE_HARFBUZZ=1 -DHAVE_LIBSNDFILE=1 -DHAVE_LIBSPEEXDSP=1 -DHAVE_MPG123=1 -DHAVE_OGGVORBIS=1 -DHAVE_OPUS=1 -DHAVE_WINE=1 -DSUPPORT_AUDIO=1 -DUSE_SDL=2 -DWANT_FMMIDI=1 -I../src -Ilib/liblcf/src -I../lib/liblcf/src -I../lib/liblcf/src/generated -isystem /usr/include/SDL2 -isystem /usr/include/pixman-1 -isystem /usr/include/freetype2 -isystem /usr/include/harfbuzz -isystem /usr/include/speex -isystem /usr/include/vorbis -isystem /usr/include/opus -O3 -DNDEBUG   -fno-math-errno -std=gnu++14 -MD -MT CMakeFiles/EasyRPG_Player.dir/src/autobattle.cpp.o -MF CMakeFiles/EasyRPG_Player.dir/src/autobattle.cpp.o.d -o CMakeFiles/EasyRPG_Player.dir/src/autobattle.cpp.o -c ../src/autobattle.cpp
2021-05-14T19:23:08.8420466Z In file included from ../src/string_view.h:23,
2021-05-14T19:23:08.8421233Z                  from ../src/utils.h:27,
2021-05-14T19:23:08.8421732Z                  from ../src/game_battler.h:31,
2021-05-14T19:23:08.8422244Z                  from ../src/autobattle.h:23,
2021-05-14T19:23:08.8422778Z                  from ../src/autobattle.cpp:17:
2021-05-14T19:23:08.8425240Z /usr/include/fmt/core.h: In instantiation of 'struct fmt::v5::formatter<nonstd::sv_lite::basic_string_view<char>, char, void>':
2021-05-14T19:23:08.8428170Z /usr/include/fmt/core.h:590:56:   required from 'static void fmt::v5::internal::value<Context>::format_custom_arg(const void*, Context&) [with T = nonstd::sv_lite::basic_string_view<char>; Context = fmt::v5::basic_format_context<std::back_insert_iterator<fmt::v5::internal::basic_buffer<char> >, char>]'
2021-05-14T19:23:08.8430677Z /usr/include/fmt/core.h:576:19:   required from 'fmt::v5::internal::value<Context>::value(const T&) [with T = nonstd::sv_lite::basic_string_view<char>; Context = fmt::v5::basic_format_context<std::back_insert_iterator<fmt::v5::internal::basic_buffer<char> >, char>]'
2021-05-14T19:23:08.8433544Z /usr/include/fmt/core.h:604:58:   required from 'constexpr fmt::v5::internal::init<Context, T, TYPE>::operator fmt::v5::internal::value<Context>() const [with Context = fmt::v5::basic_format_context<std::back_insert_iterator<fmt::v5::internal::basic_buffer<char> >, char>; T = const nonstd::sv_lite::basic_string_view<char>&; fmt::v5::internal::type TYPE = (fmt::v5::internal::type)13]'
2021-05-14T19:23:08.8437440Z /usr/include/fmt/core.h:1056:35:   required from 'typename std::enable_if<IS_PACKED, fmt::v5::internal::value<Context> >::type fmt::v5::internal::make_arg(const T&) [with bool IS_PACKED = true; Context = fmt::v5::basic_format_context<std::back_insert_iterator<fmt::v5::internal::basic_buffer<char> >, char>; T = nonstd::sv_lite::basic_string_view<char>; typename std::enable_if<IS_PACKED, fmt::v5::internal::value<Context> >::type = fmt::v5::internal::value<fmt::v5::basic_format_context<std::back_insert_iterator<fmt::v5::internal::basic_buffer<char> >, char> >]'
2021-05-14T19:23:08.8441536Z /usr/include/fmt/core.h:1114:51:   required from 'fmt::v5::format_arg_store<Context, Args>::format_arg_store(const Args& ...) [with Context = fmt::v5::basic_format_context<std::back_insert_iterator<fmt::v5::internal::basic_buffer<char> >, char>; Args = {nonstd::sv_lite::basic_string_view<char, std::char_traits<char> >, const char*}]'
2021-05-14T19:23:08.8444734Z /usr/include/fmt/core.h:1444:40:   required from 'std::__cxx11::basic_string<typename fmt::v5::internal::format_string_traits<S>::char_type> fmt::v5::format(const String&, const Args& ...) [with String = char [57]; Args = {nonstd::sv_lite::basic_string_view<char, std::char_traits<char> >, const char*}; typename fmt::v5::internal::format_string_traits<S>::char_type = char]'
2021-05-14T19:23:08.8447127Z ../src/output.h:189:22:   required from 'void Output::Debug(FmtStr&&, Args&& ...) [with FmtStr = const char (&)[57]; Args = {nonstd::sv_lite::basic_string_view<char, std::char_traits<char> >&, const char* const&}]'
2021-05-14T19:23:08.8448167Z ../src/autobattle.cpp:57:101:   required from here
2021-05-14T19:23:08.8449485Z /usr/include/fmt/core.h:349:17: error: static assertion failed: don't know how to format the type, include fmt/ostream.h if it provides an operator<< that should be used
2021-05-14T19:23:08.8450500Z    static_assert(no_formatter_error<T>::value,
2021-05-14T19:23:08.8451448Z                  ^~~~~~~~~~~~~~~~~~~~~
2021-05-14T19:23:09.4088235Z [16/342] Building CXX object CMakeFiles/EasyRPG_Player.dir/src/background.cpp.o
2021-05-14T19:23:10.2208231Z [17/342] Building CXX object CMakeFiles/EasyRPG_Player.dir/src/baseui.cpp.o
2021-05-14T19:23:10.2209041Z ninja: build stopped: subcommand failed.

[Ghabry]

The solution written in the assert (include fmt/ostream.h) works BUT it makes the build ~30% slower.

So as a workaround I suggest the following in src/string_view.h (only pay for the slow build when needed)

#if FMT_VERSION < 60000
#include <fmt/ostream.h>
#endif

[carstene1ns]

Ok, done. Player takes 7m35s: https://github.com/carstene1ns/easyrpg-player/actions/runs/845852011

[Ghabry]

Figured out how to make Player compatible with fmtlib 4.x:

https://gist.github.com/Ghabry/ce6583102dcf9706495509ea73e7de53

Note that the "configure.ac" part is incomplete. This will only work when you #include config.h like in system.h. Was not sure if this causes any problems so I left this out and you can decide if you want support for fmt 4.x with autotools or not.

[carstene1ns]

I think we should apply the 4.x patch only for release builds in obs-config repository.