Yegappan wrote:
> I am updating the Vim9 LSP plugin to support various position
> encodings (utf-8, utf-16 and utf-32).
> I ran into a problem with positioning the cursor on a multibyte
> character with composing characters.
>
> The LSP plugin uses the Vim function setcursorcharpos() to position
> the cursor. This function ignores composing characters. The LSP
> server counts the composing characters separately from
> the base character. So when using the character index returned by the
> LSP server to
> position the cursor, the cursor is placed in an incorrect column.
>
> e.g:
>
> void fn(int aVar)
> {
> printf("aVar = %d\n", aVar);
> printf("ŠŠŠŠ = %d\n", aVar);
> printf("áb́áb́ = %d\n", aVar);
> printf("ą́ą́ą́ą́ = %d\n", aVar);
> }
>
> I have tried this test with clangd, pyright and gopls language servers
> and all of them count the
> composing characters as separate characters.
>
> One approach to solve this issue is to add an optional argument to the
> setcursorcharpos() function
> that either counts or ignores composing characters. The default is to
> ignore the composing
> characters. Another approach is to add a function that computes the
> character offset ignoring the composing characters from a character
> offset that includes the composing characters.
>
> Any suggestions?
Whether to count composing characters separately or not applies to many
functions. Adding a flag to each function to specify how composing
characters are to be handled is going to require a lot of changes. And
even for setcursorcharpos() I don't see a good way to add this flag.
Assuming we have the text, using a separate function to ignore composing
characters would be a separate step and a universal solution. I suppose
it could be something like:
idx_without = charpos_dropcomposing({text}, {idx_with})
It may not be needed now, but the opposite should be possible:
idx_with = charpos_addcomposing({text}, {idx_without})
Hopefully we can think of better (shorter) names.
It can possibly already be done with a combination of byteidxcomp() and
charidx(), since these have a choice of counting composing characters or
not. That does require two function calls though.
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