Some recent warnings I got when compiling with -Wall -Wextra

[lss4]

With the latest commit I observed the following warnings when compiling code with -Wall -Wextra, which is the default warning level I currently use on my projects.

1. Some null-related warnings with json5pp::value's constructor:

json5pp/json5pp.hpp: In constructor ‘json5pp::value::value(json5pp::value::null_type)’:
json5pp/json5pp.hpp:162:19: warning: unused parameter ‘null’ [-Wunused-parameter]
  162 |   value(null_type null) noexcept : type(TYPE_NULL) {}
      |         ~~~~~~~~~~^~~~
json5pp/json5pp.hpp: In member function ‘json5pp::value& json5pp::value::operator=(json5pp::value::null_type)’:
json5pp/json5pp.hpp:594:30: warning: unused parameter ‘null’ [-Wunused-parameter]
  594 |   value& operator=(null_type null)
      |                    ~~~~~~~~~~^~~~

2. json5pp::rule::json5() (I use this to read JSON5 from std::ifstream to a json5pp::value) causes the following notes and warnings:

json5pp/json5pp.hpp:789:65: warning: unused parameter ‘manip’ [-Wunused-parameter]
  789 |   parser<((F&~C)|S)&M> operator>>(const manipulator_flags<S,C>& manip)
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
json5pp/json5pp.hpp: In member function ‘int json5pp::impl::parser<F>::skip_spaces() [with unsigned int F = 4095]’:
json5pp/json5pp.hpp:873:9: warning: this statement may fall through [-Wimplicit-fallthrough=]
  873 |         if (has_flag(flags::single_line_comment | flags::multi_line_comment)) {
      |         ^~
json5pp/json5pp.hpp:908:7: note: here
  908 |       default:
      |       ^~~~~~~
json5pp/json5pp.hpp: In member function ‘void json5pp::impl::parser<F>::parse_string(std::string&, int, const char*) [with unsigned int F = 4095]’:
json5pp/json5pp.hpp:1286:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
 1286 |           if (has_flag(flags::multi_line_string)) {
      |           ^~
json5pp/json5pp.hpp:1294:9: note: here
 1294 |         case '\n':
      |         ^~~~
json5pp/json5pp.hpp:1295:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
 1295 |           if (has_flag(flags::multi_line_string)) {
      |           ^~
json5pp/json5pp.hpp:1299:9: note: here
 1299 |         default:
      |         ^~~~~~~
json5pp/json5pp.hpp: In member function ‘void json5pp::impl::parser<F>::parse_number(json5pp::value&, int) [with unsigned int F = 4095]’:
json5pp/json5pp.hpp:1173:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
 1173 |         exp_negative = true;
      |         ~~~~~~~~~~~~~^~~~~~
json5pp/json5pp.hpp:1175:7: note: here
 1175 |       case '+':
      |       ^~~~

This is on gcc/g++ 10.2.0. I haven't noticed any major issues stemmed from those warnings yet, and as I currently have only a few places actually using json5pp::value so I'm currently not getting too many warnings from it. For now I'll suppress the warnings via -isystem to better focus on warnings coming from my own code in case there are any.

EDIT: I noticed some /* no-break */ comments. I'm not certain which compiler/editor respects this comment but g++ actually doesn't. Using // fall through suppressed the implicit fallthrough warnings for g++ according to this. Still I think a portable solution might be needed.

EDIT 2: I just found this method which works to suppress the unused parameter warnings for gcc/g++, as at one time I was dealing with a similar situation. Adding __attribute__((unused)) after the parameter that would not be used in the scope suppressed the warnings in my case. However, like the previous edit, this is probably specific to gcc/g++ and different workarounds might be needed for other compilers.

EDIT 3: Okay... it appeared I used a different method for the unused parameter warnings for the null_type value, by removing the parameter name from the prototype and declaration (leaving only the type).