Proposed resolution:

This wording is relative to N4830.

1. Modify [charconv.syn], header <charconv> synopsis, as indicated:

   […]
   // [charconv.to.chars], primitive numerical output conversion
   struct to_chars_result {
     char* ptr;
     errc ec;
     friend bool operator==(const to_chars_result&, const to_chars_result&) = default;
   };
   
   to_chars_result to_chars(char* first, char* last, see below value, int base = 10);
   to_chars_result to_chars(char* first, char* last, bool value, int base = 10) = delete;
   to_chars_result to_chars(char* first, char* last, float value);
   […]
   

[ 2019-09-14 Issue Prioritization ]

Status to Tentatively Ready and priority to 0 after eight positive votes on the reflector.

[charconv.to.chars] does not present an overload for bool (because it is neither a signed nor unsigned integer type), so an attempt to call to_chars with a bool argument would promote it to int and unambiguously call the int overload of to_chars.

This was not intended, since it is not obvious that the correct textual representation of a bool is 0/1 (as opposed to, say, "true"/"false").

The user should cast explicitly if he wants the 0/1 behavior. (Correspondingly, there is no bool overload for from_chars in the status quo, and conversions do not apply there because of the reference parameter.)