(Ruby) Character literal notation not supported for some cases

[Hirse]

Describe the issue
Only some cases of Character Literals seem to be supported.
Support is missing for the following groups of cases (in decreasing importance):

• Single slash character (?/), breaks following lines as it gets treated as starting a regex
• Escaped backslash character (?\\)
• Non-ascii character (?あ)
• Unicode using curly-bracket notation (?\u{1AF9})
• Control and Meta characters (?\C-a)

Which language seems to have the issue?
ruby

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Sample Code to Reproduce

c = ?a       #=> "a"
c = ?abc     #=> SyntaxError
c = ?\n      #=> "\n"
c = ?\s      #=> " "
c = ?\\      #=> "\\"
c = ?\u{41}  #=> "A"
c = ?\C-a    #=> "\x01"
c = ?\M-a    #=> "\xE1"
c = ?\M-\C-a #=> "\x81"
c = ?\C-\M-a #=> "\x81", same as above
c = ?あ      #=> "あ"


c = ?/          #=> /
c = ?\123       # octal bit pattern, where nnn is 1-3 octal digits ([0-7])
c = ?\xA1       # hexadecimal bit pattern, where nn is 1-2 hexadecimal digits ([0-9a-fA-F])
c = ?\uAF09     # Unicode character, where nnnn is exactly 4 hexadecimal digits ([0-9a-fA-F])
c = ?\cx        # control character, where x is an ASCII printable character
c = ?\c\M-x     # meta control character, where x is an ASCII printable character
c = ?\c?        # delete, ASCII 7Fh (DEL)
c = ?\C-?       # delete, ASCII 7Fh (DEL)

Expected behavior

Additional context
Seen in this StackExchange/CodeGolf answer: https://codegolf.stackexchange.com/a/217367/25026

->(n,g=->c,d{(1..n).map{|i|" "*(n-i)+d+" "*2*(n+i-1)+c}},l=g[?/,e=?\\].reverse){[" "*n+?_*n*2,g[e,?/],l[0..-2],l[-1].sub(/ +(?=\/)/,?_*n*2)]}

[joshgoebel]

Good find. How did you get the expected behavior shot? :) Is there a PR forthcoming? :)

I think all of these look fixable at first glance.

[Hirse]

Agreed, most should be a simple regex change, though I don't quite understand why the single unicode char (あ) is not supported currently.

I might look into a PR later, but for the expected image I manually hacked the html. :D

[joshgoebel]

I don't quite understand why the single unicode char (あ) is not supported currently.

It's not in the regex?

        begin: /\B\?(\\\d{1,3}|\\x[A-Fa-f0-9]{1,2}|\\u[A-Fa-f0-9]{4}|\\?\S)\b/

I am not sure that \S works with fancy UTF-8 stuff.

[Hirse]

\S seems to match unicode:

https://regexr.com/5jodu

[joshgoebel]

Ah, but that character does not form a word boundary so \b will abort the match.

If we're going to fix this we need variants, not one big regex. :)