Line break \R in x-mode

[robic0@…]

Bug: get_escape_R_string()

This function injects whitespace literals in the return string.
This is a problem in x-mode since the whitespace
is ignored when it's re-parsed, which then throws an exception.

---

File: boost\regex\v4\regex_traits_defaults.hpp

Function: get_escape_R_string()

template <class charT>
inline const charT* get_escape_R_string()
{
#ifdef BOOST_MSVC
#  pragma warning(push)
#  pragma warning(disable:4309 4245)
#endif

   static const charT e1[] = { '(', '?', '>', '\x0D', '\x0A', '?',
      '|', '[', '\x0A', '\x0B', '\x0C', static_cast<unsigned char>('\x85'), '\\', 'x', '{', '2', '0', '2', '8', '}',
                '\\', 'x', '{', '2', '0', '2', '9', '}', ']', ')', '\0' };
   static const charT e2[] = { '(', '?', '>', '\x0D', '\x0A', '?',
      '|', '[', '\x0A', '\x0B', '\x0C', static_cast<unsigned char>('\x85'), ']', ')', '\0' };

   charT c = static_cast<charT>(0x2029u);
   bool b = (static_cast<unsigned>(c) == 0x2029u);

   return (b ? e1 : e2);
#ifdef BOOST_MSVC
#  pragma warning(pop)
#endif
}

---

Can be fixed by converting the whitespace characters
to hex string literal.

   static const charT e1[] = { '(', '?', '>', 
      '\\', 'x', '0', 'D', '\\', 'x', '0', 'A', '?',
      '|', '[', 
      '\\', 'x', '0', 'A', '\\', 'x', '0', 'B', '\\', 'x', '0', 'C',
      '\\', 'x', '8', '5', '\\', 'x', '{', '2', '0', '2', '8', '}',
      '\\', 'x', '{', '2', '0', '2', '9', '}', ']', ')', '\0' };
   static const charT e2[] = { '(', '?', '>',
      '\\', 'x', '0', 'D', '\\', 'x', '0', 'A', '?',
      '|', '[',
      '\\', 'x', '0', 'A', '\\', 'x', '0', 'B', '\\', 'x', '0', 'C',
      '\\', 'x', '8', '5', ']', ')', '\0' };

[John Maddock]

Thanks for spotting this, fixed in ​https://github.com/boostorg/regex/commit/a32e0cc9d39f8c0886fe5576022c7bf0c9efc265