[Bug libstdc++/116903] New: c++ regex accepts } and ] as a literal character.

[fsb4000 at yandex dot ru via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116903

            Bug ID: 116903
           Summary: c++ regex  accepts } and ] as a literal character.
           Product: gcc
           Version: 14.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fsb4000 at yandex dot ru
  Target Milestone: ---

I'm not sure if this is your extension or a bug, but I found that libstdc++
accepts '}' and ']' in regex. MS STL and libc++ throw an exception for these
examples and libstdc++ prints "it's legal".

Code:
// https://godbolt.org/z/EqejrjqGP
#include <regex>

int main()
{
    try {
        std::regex r("a{0}]");
        puts("it's legal");
    } catch (std::exception& e) {
        puts(e.what());
    }
}

and

// https://godbolt.org/z/Ec4nMc9js
#include <regex>

int main()
{
    try {
        std::regex r("a{0}}");
        puts("it's legal");
    } catch (std::exception& e) {
        puts(e.what());
    }
}