Fix a compile error in C++20

[maskit]

IOBuffer.cc: In function ‘auto make_buffer_size_parser()’:
IOBuffer.cc:99:3: error: call of overloaded ‘Lexicon(<brace-enclosed initializer list>)’ is ambiguous
   99 |   }](swoc::TextView esize) -> std::optional<int> {
      |   ^
In file included from IOBuffer.cc:30:
/home/maskit/src/trafficserver/lib/swoc/include/swoc/Lexicon.h:576:1: note: candidate: ‘swoc::_1_4_6::Lexicon<E>::Lexicon(const std::initializer_list<std::tuple<E, std::basic_string_view<char, std::char_traits<char> > > >&, swoc::_1_4_6::Lexicon<E>::DefaultHandler, swoc::_1_4_6::Lexicon<E>::DefaultHandler) [with E = int; swoc::_1_4_6::Lexicon<E>::DefaultHandler = std::variant<std::monostate, int, std::basic_string_view<char, std::char_traits<char> >, std::function<int(std::basic_string_view<char, std::char_traits<char> >)>, std::function<std::basic_string_view<char, std::char_traits<char> >(int)> >]’
  576 | Lexicon<E>::Lexicon(const std::initializer_list<Pair> &items, DefaultHandler handler_1, DefaultHandler handler_2) {
      | ^~~~~~~~~~
/home/maskit/src/trafficserver/lib/swoc/include/swoc/Lexicon.h:565:1: note: candidate: ‘swoc::_1_4_6::Lexicon<E>::Lexicon(const std::initializer_list<swoc::_1_4_6::Lexicon<E>::Definition>&, swoc::_1_4_6::Lexicon<E>::DefaultHandler, swoc::_1_4_6::Lexicon<E>::DefaultHandler) [with E = int; swoc::_1_4_6::Lexicon<E>::DefaultHandler = std::variant<std::monostate, int, std::basic_string_view<char, std::char_traits<char> >, std::function<int(std::basic_string_view<char, std::char_traits<char> >)>, std::function<std::basic_string_view<char, std::char_traits<char> >(int)> >]’
  565 | Lexicon<E>::Lexicon(const std::initializer_list<Definition> &items, DefaultHandler handler_1, DefaultHandler handler_2) {
      | ^~~~~~~~~~

[maskit]

Works for C++20 but not C++17

[brbzull0]

I think this can be handled by swoc::Lexicon and not by us here. @SolidWallOfCode ?

[SolidWallOfCode]

Talk to @cmcfarlen - it's a bit of an odd use.

[SolidWallOfCode]

I've been investigating this and I think the problem is the string_view constructor that takes iterators, which is new in C++20. This makes something like { value, { "name1", "name2"}} convertible to Pair{value, string_view{"name1", "name2")} which wasn't previously the case. I am pondering a couple of different approaches.

[dragon512]

I think this is the wrong fix.

it should be

--- a/iocore/eventsystem/IOBuffer.cc
+++ b/iocore/eventsystem/IOBuffer.cc
@@ -79,7 +79,7 @@ init_buffer_allocators(int iobuffer_advice)
 auto
 make_buffer_size_parser()
 {
-  return [l = swoc::Lexicon<int>{
+  return [l = swoc::Lexicon<int>{swoc::Lexicon<int>::with_multi
             {{0, {"128"}},
              {1, {"256"}},
              {2, {"512"}},

This should solve the issues with compiling with G++ 8.3 and above

[maskit]

#9700 will resolve the issue.