Warning: msvc 16.10-pre3 clashes with {fmt}

[DanielaE]

For some not yet investigated reason, <format> from the STL gets pulled into {fmt}'s test for compile.h. This might affect user code as well. Interesting times ...

Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30035 for x64
compile-test.cc
E:\fmt-module\fmtlib\include\fmt/compile.h(325): error C2668: 'std::make_format_args': ambiguous call to overloaded function
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview-IDE\VC\Tools\MSVC\14.29.30035\include\format(2848): note: could be 'auto std::make_format_args<fmt::v7::basic_format_context<std::back_insert_iterator<std::string>,char>,_Ty>(const _Ty &)' [found using argument-dependent lookup]
        with
        [
            _Ty=std::chrono::duration<__std_tzdb_epoch_milli,std::milli>
        ]
E:\fmt-module\fmtlib\include\fmt\core.h(1640): note: or       'fmt::v7::format_arg_store<fmt::v7::basic_format_context<std::back_insert_iterator<std::string>,char>,_Ty> fmt::v7::make_format_args<fmt::v7::basic_format_context<std::back_insert_iterator<std::string>,char>,_Ty>(const _Ty &)'
        with
        [
            _Ty=std::chrono::duration<__std_tzdb_epoch_milli,std::milli>
        ]
E:\fmt-module\fmtlib\include\fmt/compile.h(323): note: while trying to match the argument list '(const _Ty)'
        with
        [
            _Ty=std::chrono::duration<__std_tzdb_epoch_milli,std::milli>
        ]
E:\fmt-module\fmtlib\include\fmt/compile.h(559): note: see reference to function template instantiation 'OutputIt fmt::v7::detail::spec_field<char_type,std::chrono::duration<__std_tzdb_epoch_milli,std::milli>,0>::format<std::back_insert_iterator<std::string>,_Ty>(OutputIt,const _Ty &) const' being compiled
        with
        [
            OutputIt=std::back_insert_iterator<std::string>,
            _Ty=std::chrono::duration<__std_tzdb_epoch_milli,std::milli>
        ]
E:\fmt-module\fmtlib\include\fmt/compile.h(561): note: see reference to function template instantiation 'OutputIt fmt::v7::detail::spec_field<char_type,std::chrono::duration<__std_tzdb_epoch_milli,std::milli>,0>::format<std::back_insert_iterator<std::string>,_Ty>(OutputIt,const _Ty &) const' being compiled
        with
        [
            OutputIt=std::back_insert_iterator<std::string>,
            _Ty=std::chrono::duration<__std_tzdb_epoch_milli,std::milli>
        ]
E:\fmt-module\fmtlib\include\fmt/compile.h(575): note: see reference to function template instantiation 'std::basic_string<char,std::char_traits<char>,std::allocator<char>> fmt::v7::format<T,_Ty,char,0>(const CompiledFormat &,const _Ty &)' being compiled
        with
        [
            T=fmt::v7::detail::spec_field<char_type,std::chrono::duration<__std_tzdb_epoch_milli,std::milli>,0>,
            _Ty=std::chrono::duration<__std_tzdb_epoch_milli,std::milli>,
            CompiledFormat=fmt::v7::detail::spec_field<char_type,std::chrono::duration<__std_tzdb_epoch_milli,std::milli>,0>
        ]
E:\fmt-module\fmtlib\test\compile-test.cc(97): note: see reference to function template instantiation 'std::basic_string<char,std::char_traits<char>,std::allocator<char>> fmt::v7::format<compile_test_format_specs_Test::TestBody::<lambda_2>::()::FMT_COMPILE_STRING,std::chrono::duration<__std_tzdb_epoch_milli,std::milli>,0>(const S &,std::chrono::duration<__std_tzdb_epoch_milli,std::milli> &&)' being compiled
        with
        [
            S=compile_test_format_specs_Test::TestBody::<lambda_2>::()::FMT_COMPILE_STRING
        ]
E:\fmt-module\fmtlib\include\fmt/compile.h(324): error C2530: 'vargs': references must be initialized
E:\fmt-module\fmtlib\include\fmt/compile.h(323): error C3536: 'vargs': cannot be used before it is initialized
E:\fmt-module\fmtlib\include\fmt/compile.h(326): error C2664: 'fmt::v7::basic_format_context<std::back_insert_iterator<std::string>,char>::basic_format_context(OutputIt,fmt::v7::basic_format_args<fmt::v7::basic_format_context<OutputIt,char>>,fmt::v7::detail::locale_ref)': cannot convert argument 2 from 'int' to 'fmt::v7::basic_format_args<fmt::v7::basic_format_context<std::back_insert_iterator<std::string>,char>>'
        with
        [
            OutputIt=std::back_insert_iterator<std::string>
        ]
E:\fmt-module\fmtlib\include\fmt/compile.h(323): note: No constructor could take the source type, or constructor overload resolution was ambiguous
E:\fmt-module\fmtlib\include\fmt\core.h(1536): note: see declaration of 'fmt::v7::basic_format_context<std::back_insert_iterator<std::string>,char>::basic_format_context'

Build failed.

[DanielaE]

Injecting an #include <format> into every TU shows that this is the only place where such a clash in happening in the tests.