[Issue]: yagChar is Not up to Spec

[l-zeuch]

Expected Behaviour

According to the Go specification on Rune literals¹, following sequences are allowed:

'a'
'ä'
'本'
'\t'
'\000'
'\007'
'\377'
'\x07'
'\xff'
'\u12e4'
'\U00101234'
'\''         // rune literal containing single quote character

Thus, it is expected that the yagChar syntax group also recognises those.

Actual Behaviour

Instead, we see the following behaviour:

Here, through some tricky code, we try to let the user know when they are creating/using an illegal rune literal. However, according to the Go specification¹ the sequences in the above screenshot are actually valid, as I copied them directly from there.

Steps to Reproduce

1. Go to the Go spec (https://go.dev/ref/spec#Rune_literals)
2. copy any valid rune literal longer than two characters
3. Insert to a *.yag file (or any accepted file extension)
4. See screenshot

Additional Context

I understand that validating Unicode may be a hard task to do; if this seems unfeasible, we could just resort to finding the longest Unicode sequence available and use that as the maximum allowed.

If memory serves me right, Unicode ranges from 0 to 0x10FFFF, though not all are assigned. Perhaps we could call out to Python if we really want to validate any given Unicode sequence², and maybe even display it as virtual text of sorts.³⁴⁵
(Given that the user's (Neo)Vim supports said virtual text)

Code of Conduct

• I agree to follow this project's Code of Conduct.

Footnotes

1. https://go.dev/ref/spec#Rune_literals ↩ ↩²

2. https://docs.python.org/3/howto/unicode.html ↩

3. https://neovim.io/doc/user/api.html#api-extmark ↩

4. https://vimhelp.org/textprop.txt.html ↩

5. https://vimhelp.org/textprop.txt.html#virtual-text ↩