‘fmt’ is not a constant expression

[bigwhite37]

When I compiled seastar on ubuntu 21.04 with gcc 11.2.0, the configure command is,

$ ./configure.py --mode=debug --c++-dialect=c++2b

then I got the compile error:

In file included from /root/code/cu/seastar/include/seastar/util/backtrace.hh:30,
                 from /root/code/cu/seastar/include/seastar/core/task.hh:26,
                 from /root/code/cu/seastar/include/seastar/core/future.hh:24,
                 from /root/code/cu/seastar/include/seastar/core/semaphore.hh:24,
                 from /root/code/cu/seastar/src/core/semaphore.cc:23:
/root/code/cu/seastar/include/seastar/core/print.hh: In instantiation of ‘seastar::sstring seastar::format(const char*, A&& ...) [with A = {std::basic_string_view<char, std::char_traits<char> >&}; seastar::sstring = seastar::basic_sstring<char, unsigned int, 15>]’:
/root/code/cu/seastar/src/core/semaphore.cc:70:22:   required from here
/root/code/cu/seastar/include/seastar/core/print.hh:136:19:   in ‘constexpr’ expansion of ‘fmt::v8::basic_format_string<char, std::basic_string_view<char, std::char_traits<char> >&>(fmt)’
/root/code/cu/seastar/include/seastar/core/print.hh:136:19: error: ‘fmt’ is not a constant expression
  136 |     fmt::format_to(out, fmt, std::forward<A>(a)...);
      |     ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[ 17%] Building CXX object CMakeFiles/seastar.dir/src/http/routes.cc.o
make[2]: *** [CMakeFiles/seastar.dir/build.make:508: CMakeFiles/seastar.dir/src/core/semaphore.cc.o] Error 1
make[2]: *** Waiting for unfinished jobs....
In file included from /root/code/cu/seastar/src/core/memory.cc:57:
/root/code/cu/seastar/include/seastar/core/print.hh: In instantiation of ‘seastar::sstring seastar::format(const char*, A&& ...) [with A = {long unsigned int&, long unsigned int&}; seastar::sstring = seastar::basic_sstring<char, unsigned int, 15>]’:
/root/code/cu/seastar/src/core/memory.cc:79:40:   required from here
/root/code/cu/seastar/include/seastar/core/print.hh:136:19:   in ‘constexpr’ expansion of ‘fmt::v8::basic_format_string<char, long unsigned int&, long unsigned int&>(fmt)’
/root/code/cu/seastar/include/seastar/core/print.hh:136:19: error: ‘fmt’ is not a constant expression
  136 |     fmt::format_to(out, fmt, std::forward<A>(a)...);
      |     ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /root/code/cu/seastar/include/seastar/util/backtrace.hh:30,
                 from /root/code/cu/seastar/src/core/on_internal_error.cc:23:
/root/code/cu/seastar/include/seastar/core/print.hh: In instantiation of ‘seastar::sstring seastar::format(const char*, A&& ...) [with A = {const char*, seastar::tasktrace}; seastar::sstring = seastar::basic_sstring<char, unsigned int, 15>]’:
/root/code/cu/seastar/include/seastar/util/backtrace.hh:187:58:   required from ‘seastar::internal::backtraced<Exc>::backtraced(Args&& ...) [with Args = {std::runtime_error}; Exc = std::runtime_error]’
/root/code/cu/seastar/include/seastar/util/backtrace.hh:215:67:   required from ‘std::__exception_ptr::exception_ptr seastar::make_backtraced_exception_ptr(Args&& ...) [with Exc = std::runtime_error; Args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
/root/code/cu/seastar/include/seastar/util/backtrace.hh:231:62:   required from ‘void seastar::throw_with_backtrace(Args&& ...) [with Exc = std::runtime_error; Args = {std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
/root/code/cu/seastar/src/core/on_internal_error.cc:41:49:   required from here
/root/code/cu/seastar/include/seastar/core/print.hh:136:19:   in ‘constexpr’ expansion of ‘fmt::v8::basic_format_string<char, const char*, seastar::tasktrace>(fmt)’
/root/code/cu/seastar/include/seastar/core/print.hh:136:19: error: ‘fmt’ is not a constant expression
  136 |     fmt::format_to(out, fmt, std::forward<A>(a)...);
      |     ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This error maybe relate to this issue.

After I changing the code in print.hh which lead to compile error:

// before changing
fmt::format_to(out, fmt, std::forward<A>(a)...);

// after changing
fmt::format_to(out, fmt::runtime(fmt), std::forward<A>(a)...);

the compile error is fixed.

[deafwolf]

looks this issue has been solved dfb6286