feat: add completionInPreview option and preview filetype handling

[Konfekt]

A stab at https://github.com/yegappan/lsp/issues/688 ; if @813ethan could test and comment

[813ethan]

looks nice, is there a reason why the preview window is so small? compared to :LspHover i think the builtins line could be removed to save some space

Also is it possible if the preview window can be automatically closed after exiting the autocompletion menu? like jedi-vim and ycm

[813ethan]

now the preview closes after the autocompletion got selected, but it's still opened when there're no completions

also the preview window's size is still too small?

https://github.com/user-attachments/assets/2c94eaf8-bd01-4f16-add2-4ad57015a8ab

[813ethan]

ok tried testing it for a bit, seems like

https://github.com/yegappan/lsp/blob/c57a2615891dc5400a63d8a54552873368877b5c/autoload/lsp/completion.vim#L277

the preview window's was initialized with 'Lazy doc', maybe this messed the window size up?

also can i suggest if there can be a toggle for (not) autoclosing the preview window? if it's not hard to implement

[Konfekt]

I have no idea why the preview window height is not sufficiently high; by default it should be (=12) and Vim respect it?

[813ethan]

the height seems to change accordingly with the documentation's length (this is ycm btw)

https://github.com/user-attachments/assets/9caa6f03-b0e4-4df1-a3c9-a746477759a9

[813ethan]

maybe resize the window after the doc is shown? This works for me

*** completion.vim.old	2025-11-05 08:35:36.036497263 +1100
--- completion.vim	2025-11-05 08:36:08.768497250 +1100
***************
*** 456,461 ****
--- 456,462 ----
        infoText->append(0)
        [1, 1]->cursor()
        exe $'setlocal ft={infoKind}'
+       exe 'resize' &previewheight
        :wincmd p
      catch /E441/ # No preview window
      endtry

[Konfekt]

Thank you! We should be good to go @yegappan

[813ethan]

One more problem, there's this error showing up when im using preview with clangd?

this is my lsp config:

{
          'name': 'clangd',
          'filetype': ['c', 'cpp'],
          'path': TERMUX_PREFIX .. '/usr/bin/clangd',
          'args': ['--background-index', '--clang-tidy']
}

All good otherwise, the error didn't happen with other clients like python-language-server

[Konfekt]

Could it be related to the just added

exe 'resize' &previewheight

?

Does it still show up without it? When using silent! exe ... or better try .. catch E565 ... endtry?

[813ethan]

Could it be related to the just added

exe 'resize' &previewheight

?

error still shows up with the line removed

Does it still show up without it? When using silent! exe ... or better try .. catch E565 ... endtry?

same error with try ... catch, prolly caused by something else

[813ethan]

ok nvm try ... catch E565 here silenced the errors, but markdown isn't applied to the preview window

https://github.com/yegappan/lsp/blob/5ded99487aab03513120a758fd5222d413284bf4/autoload/lsp/completion.vim#L631-L635

https://github.com/user-attachments/assets/85163cfa-4081-4233-850d-232720078e87

the error still exists after removing setlocal ft=lspgfm

[813ethan]

https://groups.google.com/g/vim_dev/c/UX9-Dgw86xA maybe this is related?

[Konfekt]

Patch 8.2.2427 and 8.2.2426 disallow changing windows in the completefunc.

So with

   :wincmd P 
   setlocal ft=lspgfm 

make sure that P does not jump to the preview window

[813ethan]

Patch 8.2.2427 and 8.2.2426 disallow changing windows in the completefunc.

So with

   :wincmd P 
   setlocal ft=lspgfm 

make sure that P does not jump to the preview window

im unsure how it works, there's no error when im using python lsp, it only appears when using clangd

[Konfekt]

Can you try to make sense of the solution https://github.com/justmao945/vim-clang/pull/140 ?

[813ethan]

Can you try to make sense of the solution justmao945/vim-clang#140 ?

it tried to move the problematic calls away from the autocomplete function?

I'm not an expert about the internals of this plugin (lsp), so i don't know if there's a way to adapt that here, not counting that this plugin is not clangd specific

yet something I noticed is that in python-language-server, LspSetPopupFileType() which causes the error was never called,

while clangd never uses lazy loading (lspserver.completionLazyDoc) and renders the documentation directly instead, maybe it's something about it?

[Konfekt]

it tried to move the problematic calls away from the autocomplete function?

Yes, could you distill which?

[813ethan]

my understanding is LspSetPopupFileType() is called to setup the completion popup's markdown highlighting, while it works for popup windows, it fails with preview windows bc of the error,

while lazy loading uses ShowCompletionDocumentation(), which also setups the markdown but didn't get any errors

maybe something with the implementation or timing of those functions? I have no idea

[Konfekt]

Thank you, so doing it the roundabout ShowCompletionDocumentation() way

#  autoload/lsp/completion.vim (lines 453-460)
  :wincmd P
  :setlocal modifiable
  bufnr()->deletebufline(1, '$')
  infoText->append(0)
  [1, 1]->cursor()
 setlocal ft=lspgfm
 :wincmd p
catch /E441/ # No preview window

solves that problem?

[813ethan]

ok nvm try ... catch E565 here silenced the errors, but markdown isn't applied to the preview window

https://github.com/yegappan/lsp/blob/5ded99487aab03513120a758fd5222d413284bf4/autoload/lsp/completion.vim#L631-L635

screen-20251105-181844.2.mp4 the error still exists after removing setlocal ft=lspgfm

won't, the error will still happen with :wincmd P..

[813ethan]

https://github.com/yegappan/lsp/blob/5ded99487aab03513120a758fd5222d413284bf4/autoload/lsp/completion.vim#L763-L766

actually can we even change the state of the preview window during CompleteChanged

[Konfekt]

Changing windows while inside a completion function is forbidden now.

I think changing means less ambiguously switching here; so we can still change, say the filetype, but have to stay inside the window

[Konfekt]

Here's the corresponding fix for php complete

[Konfekt]

Thank you, so doing it the roundabout ShowCompletionDocumentation() way

#  autoload/lsp/completion.vim (lines 453-460)
  :wincmd P
  :setlocal modifiable
  bufnr()->deletebufline(1, '$')
  infoText->append(0)
  [1, 1]->cursor()
 setlocal ft=lspgfm
 :wincmd p
catch /E441/ # No preview window

How come then this doesn't give any errors ?

[Konfekt]

More exactly, the file type is correctly set

[Konfekt]

For short, get the popup window id and then call win_execute(..) to change it, say &filetype. Could you look into that?

[813ethan]

Thank you, so doing it the roundabout ShowCompletionDocumentation() way

#  autoload/lsp/completion.vim (lines 453-460)
  :wincmd P
  :setlocal modifiable
  bufnr()->deletebufline(1, '$')
  infoText->append(0)
  [1, 1]->cursor()
 setlocal ft=lspgfm
 :wincmd p
catch /E441/ # No preview window

How come then this doesn't give any errors ?

It wasn't run on CompleteChanged, it's a separate process called (during the completion?) from lspserver.vim

[813ethan]

Changing windows while inside a completion function is forbidden now.

I think changing means less ambiguously switching here; so we can still change, say the filetype, but have to stay inside the window

the buffer is still being changed via the markdown renderer (lspgfm.vim)

tried setting the file type indirectly via

setbufvar(winbufnr(winnr('#')), '&ft', 'lspgfm')

but it gives another error

[Konfekt]

The culprit is the wincmd p/P dance; instead, get the popup window id and then call win_execute(..) to change &filetype

[813ethan]

Changing windows while inside a completion function is forbidden now.

I think changing means less ambiguously switching here; so we can still change, say the filetype, but have to stay inside the window

the buffer is still being changed via the markdown renderer (lspgfm.vim)

tried setting the file type indirectly via

setbufvar(winbufnr(winnr('#')), '&ft', 'lspgfm')

but it gives another error

This changes the &filetype of the preview buffer, without doing the wincmdP/p dance.

how can I get the window id for win_execute(...)?