Like most Vim/Neovim users I’ve built up a set of plugins and config files over the years that get the text editor customized for me. If you’re interested in my current setup you can see it in my dotfiles repo.
Since most of the time I’m adding a new plugin or setting individually, I can usually work out the culprit when Neovim starts running much slower. However, over the past few weeks I’ve had a particular issue with eruby files and there was no obvious cause.
I thought commenting out recent changes to my config, including new plugins, would be a good start. Eventually I got down to loading with no plugins and the default config, but still the issue persisted.
This is where I went searching for help and discovered the the built-in profiling tool. It is really simple to run:
:profile start profile.log :profile file * :profile func * [[ Trigger the slow action here ]] :profile pause
Inspecting your generated log file will show a list of the slowest functions, at the top of the list for me was the cause of my slow eruby files.
FUNCTIONS SORTED ON TOTAL TIME count total (s) self (s) function 6 95.409081 0.015457 <SNR>14_LoadFTPlugin() 80 0.321129 0.008854 airline#check_mode() 16 0.305660 0.041821 airline#highlighter#highlight() 1749 0.213133 0.108977 airline#highlighter#get_highlight() 365 0.199579 0.019541 <SNR>82_exec_separator() 819 0.191419 0.054809 airline#highlighter#exec() 33 0.175094 0.002036 <SNR>112_NeoVimCallback() 12 0.171814 0.001186 <SNR>108_ExitCallback() 11 0.166302 0.001700 <SNR>107_HandleExit() 11 0.155716 0.008071 ale#engine#HandleLoclist() 12 0.108573 0.000808 airline#extensions#tabline#get() 12 0.107765 0.002524 airline#extensions#tabline#buffers#get() 6 0.101130 0.000250 ale#events#LintOnEnter() 6 0.100799 0.000365 ale#Queue() 6 0.099583 0.001838 <SNR>100_Lint() 6 0.097989 0.003567 17() 730 0.097386 0.010310 airline#themes#get_highlight() 18 0.096341 0.017089 14() 6 0.095190 0.002562 ale#engine#RunLinters() 3498 0.088748 <SNR>82_get_syn()
95 seconds in one function!
93.687760 let &l:path = s:path . (s:path =~# ',$\|^$' ? '' : ',') . &l:path
Searching through the rest of the log even gave me the specific line of ftplugin/eruby.vim causing the issue. Unfortunately my vimscript knowledge is not up to fixing this, but commenting it out appears to be enough for now without any other side effects.
For more details on the profile feature there’s a detailed help doc at
:help profile, it can be limited to specific files too, useful if you’re debugging your own config or a particular plugin.