Report diagnostic error on user interface

[yanminhui]

Search before asking

• I searched the issues and found no similar issues.

What happened + What you expected to happen

#include <struct_pack/struct_pack.hpp>

struct person {
  int age;
  std::string name;
  person() = default;
};

template <class T>
requires std::is_aggregate_v<T>
void serialize(T&& t) {
    auto _ = struct_pack::serialize(std::forward<T>(t));
}

int main() {
#if defined(DIAGNOSTIC_REQUIRED)
    serialize(person{});
#else
    auto _ = struct_pack::serialize(person{});
#endif
}

It will produce too many error informations occupying the entire screen, and user may be can't understand.

admin@bryan-mbam2 yltexample % clang++ -std=c++20 main.cpp -I ~/repos/yalantinglibs/include
In file included from main.cpp:1:
In file included from /Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack.hpp:22:
In file included from /Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack/struct_pack_impl.hpp:41:
/Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack/reflection.hpp:459:7: error: static_assert failed due to requirement '!sizeof(person)' "empty struct/class is not allowed!"
      static_assert(!sizeof(type), "empty struct/class is not allowed!");
      ^             ~~~~~~~~~~~~~

... 省略编译错误信息 ...

/Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack/struct_pack_impl.hpp:1640:32: error: call to consteval function 'struct_pack::detail::packer<struct_pack::detail::memory_writer, person>::calculate_hash_head<{0}, person>' is not a constant expression
    constexpr auto hash_head = calculate_hash_head<conf, T, Args...>() |
                               ^
/Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack/struct_pack_impl.hpp:1643:19: error: constexpr if condition is not a constant expression
    if constexpr (hash_head % 2) {  // has more metainfo
                  ^~~~~~~~~~~~~
/Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack/struct_pack_impl.hpp:1643:19: note: initializer of 'hash_head' is not a constant expression
/Users/admin/repos/yalantinglibs/include/struct_pack/struct_pack/struct_pack_impl.hpp:1640:20: note: declared here
    constexpr auto hash_head = calculate_hash_head<conf, T, Args...>() |
                   ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

Report diagnostic errors on user interfaces would be better for user, for example:

admin@bryan-mbam2 yltexample % clang++ -std=c++20 main.cpp -I ~/repos/yalantinglibs/include -DDIAGNOSTIC_REQUIRED
main.cpp:17:5: error: no matching function for call to 'serialize'
    serialize(person{});
    ^~~~~~~~~
main.cpp:11:6: note: candidate template ignored: constraints not satisfied [with T = person]
void serialize(T&& t) {
     ^
main.cpp:10:10: note: because 'std::is_aggregate_v<person>' evaluated to false
requires std::is_aggregate_v<T>
         ^
1 error generated.

Reproduction way

Anything else

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

[poor-circle]

Well, We are trying to add some method so that struct_pack could support non-aggregate-type. But you are right, there are too many error now, and we should add some concept to simply the compile error output.