FMT_STRING text align fails with custom operator<<

[Naios]

bd88040

It seems like this issue was introduced between 3860edc and bd88040.

Valid on:

• Clang 10
• GCC 10.1
• MSVC 16.5.4

Minimal reproducible example:

https://gcc.godbolt.org/z/5CYkGG

#include <fmt/chrono.h>
#include <fmt/compile.h>
#include <fmt/core.h>
#include <fmt/format.h>
#include <fmt/ostream.h>
#include <fmt/compile.h>
#include <fmt/color.h>
#include <ostream>

struct custom_print {
  friend std::ostream& operator << (std::ostream& os, custom_print const&) {
      return os << "huhu";
  }
};

int main() {
    fmt::format(FMT_STRING("{:<7}"), custom_print{});
    return 0;
}

Error message:

In file included from <source>:2:

In file included from /opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/chrono.h:16:

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/format.h:2703:27: error: constexpr variable 'invalid_format' must be initialized by a constant expression

  FMT_CONSTEXPR_DECL bool invalid_format = internal::do_check_format_string<

                          ^                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/core.h:1655:3: note: in instantiation of function template specialization 'fmt::v6::internal::check_format_string<custom_print, FMT_COMPILE_STRING, 0>' requested here

  check_format_string<Args...>(format_str);

  ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/core.h:1747:17: note: in instantiation of function template specialization 'fmt::v6::internal::make_args_checked<custom_print, FMT_COMPILE_STRING, char>' requested here

      internal::make_args_checked<Args...>(format_str, args...));

                ^

<source>:18:10: note: in instantiation of function template specialization 'fmt::v6::format<FMT_COMPILE_STRING, custom_print, char>' requested here

    fmt::format(FMT_STRING("{:<7}"), custom_print{});

         ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/format.h:2638:12: note: non-constexpr function 'parse' cannot be used in a constant expression

  return f.parse(ctx);

           ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/format.h:2669:33: note: in call to 'parse_format_specs(checker.context_)'

    return arg_id_ < num_args ? parse_funcs_[arg_id_](context_) : begin;

                                ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/format.h:2615:21: note: in call to '&checker->on_format_specs(&"{:<7}"[2], &"{:<7}"[5])'

        p = handler.on_format_specs(p + 1, end);

                    ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/format.h:2696:3: note: in call to 'parse_format_string({&"{:<7}"[0], 5}, checker)'

  parse_format_string<true>(s, checker);

  ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/format.h:2703:44: note: in call to 'do_check_format_string({&"{:<7}"[0], 5}, {})'

  FMT_CONSTEXPR_DECL bool invalid_format = internal::do_check_format_string<

                                           ^

/opt/compiler-explorer/libs/fmt/6.2.1/include/fmt/ostream.h:113:8: note: declared here

  auto parse(basic_format_parse_context<Char>& ctx) -> decltype(ctx.begin()) {

       ^

1 error generated.

Compiler returned: 1

[vitaut]

Fixed in 943532f. Thanks for reporting.