Ignore buffers without language servers

[YaLTeR]

Describe the bug

Running language client commands in buffers without language servers still tries to communicate the requests to the language client binary. This has two severe effects:

1. The buffer filename is fetched (LSP#filename). This takes a really long while for files on slow network mounts.
2. The full text of the buffer is sent using JSON. This takes a really long while for very large files (think strace logs).

I'm running into this because of LanguageClient#handleCursorMoved (set-up automatically and does LSP#filename) and because of my auto-hover on cursor moved setup. I can't even disable it for irrelevant buffers because there doesn't seem to be any way to check if the language client works for the current buffer (the autocommands are only fired on server start/stop so they aren't really useful here). Either way I think it should be done automatically.

Here's the profile for moving around a network file with stock min-vimrc:

FUNCTION  LSP#filename()
    Defined: ~/.config/nvim/plugged/LanguageClient-neovim/autoload/LSP.vim line 3
Called 198 times
Total time:   5.045398
 Self time:   5.045398

count  total (s)   self (s)
                                " When executing autocommand, `%` might have already changed.
  198              5.038637     let l:filename = expand('<afile>:p')
  198              0.000953     if !l:filename
  198              0.003873         let l:filename = expand('%:p')
  198              0.000377     endif
  198              0.000672     return l:filename

FUNCTIONS SORTED ON TOTAL TIME
count  total (s)   self (s)  function
  198   5.114235   0.024005  LanguageClient#handleCursorMoved()
  198   5.045398             LSP#filename()
  198   0.034872   0.020608  LanguageClient#Notify()
  198   0.033183             <SNR>15_Highlight_Matching_Pair()
  198   0.008365             LanguageClient#Write()
  198   0.007587   0.004934  LSP#position()
  198   0.005900             <SNR>31_SkipSendingMessage()
  198   0.002373             LSP#viewport()
  198   0.001383             LSP#line()
  198   0.001270             LSP#character()

FUNCTIONS SORTED ON SELF TIME
count  total (s)   self (s)  function
  198              5.045398  LSP#filename()
  198              0.033183  <SNR>15_Highlight_Matching_Pair()
  198   5.114235   0.024005  LanguageClient#handleCursorMoved()
  198   0.034872   0.020608  LanguageClient#Notify()
  198              0.008365  LanguageClient#Write()
  198              0.005900  <SNR>31_SkipSendingMessage()
  198   0.007587   0.004934  LSP#position()
  198              0.002373  LSP#viewport()
  198              0.001383  LSP#line()
  198              0.001270  LSP#character()

Environment

• neovim/vim version (nvim --version or vim --version): 0.4.3
• This plugin version (git rev-parse --short HEAD): 7c741d0
• This plugin's binary version (bin/languageclient --version): 0.1.156
• Minimal vimrc content:
  min-vimrc.vim and open a network file, or add the following and open a network or a very large file

function! DoNothingHandler(output)
endfunction

autocmd CursorMoved * call LanguageClient_textDocument_hover({'handle': v:true}, 'DoNothingHandler')

To Reproduce

Steps to reproduce the behavior:

1. Make a very large file, like strace some program to get a 9 MB text file.
2. nvim -u min-vimrc.vim that-file
3. Try to move the cursor around.
4. It's really slow.

Current behavior

The vimscript part of the language client tries to do things on all buffers.

Expected behavior

It checks a buffer-local "is language server running here" variable and if that's false does nothing immediately.

[martskins]

@YaLTeR #1121 will make this a lot better I presume. It won't stop LCN from calling the vimscript functions but it will stop it from making the calls to the server, so I suppose it should make things a lot better for you.

[martskins]

Actually, just pushed another commit that prevents setting the autocmds for the languages that don't have a serverCommand configured. So that PR should now address this completely. If you are willing to give that a try that would be great.

[martskins]

Closing via #1121