Highlighted cursor position breaks after surrogate pairs

[dzaima]

As can be seen in https://asciinema.org/a/AxH57hTJctdztmBaJ2bBTS7nP, characters, which in JavaScript are represented as surrogate pairs, break cursor highlight positioning, due to the position being calculated in terms of JavaScript characters, not Unicode codepoints.

One possible fix is available here; in my testing, that makes such surrogate pair characters work perfectly. (feel free to pull that commit directly to main, modify/copy as needed, or request a PR)

This fix is largely independent of the larger problem around grapheme clusters/wcwidth, but it doesn't make it worse (or, in fact, even makes the cursor be positioned correctly, but that doesn't really mean much if the VT output itself is broken).

[ku1ik]

Thanks. This is useful 👍 I'll keep it open until we solve wcwidth-related core problem, and will revisit this then.