Hi folks,

I was reading the [lex.ccon] section of the current draft and noticed an
oddity in the hexadecimal-escape-sequence
<https://eel.is/c++draft/lex.ccon#nt:hexadecimal-escape-sequence>
production:

*hexadecimal-escape-sequence:*

\x *hexadecimal-digit-sequence*
*hexadecimal-escape-sequence hexadecimal-digit*
\x{ *simple-hexadecimal-digit-sequence* }

The combination of the 2nd and 3rd rules seems to say that \x{20}20 should
be parsed as a hex escape sequence (presumably representing u+2020). Octal
doesn't have this issue as *octal-escape-sequence* doesn't have a recursive
definition.

I tried this on Godbolt. GCC and Clang interpret '\x{20}20' as a
multicharacter literal and "\x{20}{20}" as the string " 20". MSVC and icc
appear not to support \x{}.

I'd guess this isn't intentional as it would defeat the purpose of having
\x{} sequences? At least two implementations seem to agree.

Fraser