Borders are rendered with ASCII characters even if non-ASCII border characters have single width

[kg8m]

Hi. Thanks for your great developing. No vim-lsp, no my Vim life.

I have an issue that floating window borders are always rendered with ASCII characters if ambiwidth option is double. But non-ASCII border characters, e.g., ─, ┌, and so on, can have single width even if ambiwidth is double. For example, setcellwidths([[0x2500, 0x257f, 1]]) makes the non-ASCII border characters single width. I usually set ambiwidth as double for some Japanese symbols and use setcellwidths() for preventing broken layout. But I want to show borders with non-ASCII characters.

I think there are some choices:

1. Use strdisplaywidth() instead of ambiwidth
   • Use non-ASCII characters if strdisplaywidth() returns 1
2. Add an configuration variable for whether ASCII or non-ASCII is used for borders
   • e.g., let g:lsp_borders_with_ascii = v:false
3. Add an configuration varaible what characters to use for borders
   • e.g., let g:lsp_border_characters = ['─', '│', '─', '│', '┌', '┐', '┘', '└']
4. Add an configuration variable for popup options
   • e.g., let g:lsp_float_options = { 'borderchars': ['─', '│', '─', '│', '┌', '┐', '┘', '└'] }
5. Any other ideas?

Could you please give me feedbacks or your thoughts?

Best regards.

[kg8m]

Note: I tried to change border characters with lsp_float_opened user event and popup_setoptions() as following.

autocmd User lsp_float_opened call OnFloatOpened()

function OnFloatOpened() abort
  let winid = lsp#ui#vim#output#getpreviewwinid()

  if winid
    call popup_setoptions(winid, #{
      borderchars: ['─', '│', '─', '│', '┌', '┐', '┘', '└'],
      padding: [0, 0, 0, 1],
    })
  endif
endfunction

But it sometimes doesn't work:

• Signature helps in Insert mode: OK
• Hover in Normal mode with :LspHover: NG (ASCII characters are used)
• Previews on completion: NG (ASCII characters are used)

Maybe, this difference is caused because the signature helps are implemented in autoload/lsp/ui/vim/output.vim#L117-L162 but hover and completion previews are implemented in autoload/vital/_lsp/VS/Vim/Window/FloatingWindow.vim#L451-L477.

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