How To Troubleshoot Vim Autocomplete Not Working?

When Vim's autocomplete stops working, it's usually a configuration issue. First, I check if the plugin is loaded. Run ':scriptnames' to see if the autocomplete plugin appears. If not, your plugin manager might not be loading it. For 'vim-plug', add 'Plug 'plugin/name'' to your vimrc and run ':PlugInstall'. Next, verify the autocomplete trigger. Some plugins use '' or ''. Test these keys in insert mode.
If the plugin loads but doesn't work, inspect the log files. For 'coc.nvim', run ':CocOpenLog' to check for errors. Sometimes, the language server crashes silently. Restarting Vim or the server might help. Also, ensure your Vim version supports the plugin. Run ':version' to check for features like '+python3' or '+lua'.
Another common issue is the completion menu not appearing. Adjust 'pumheight' with ':set pumheight=10' to ensure it displays. If you're using 'neovim', some plugins require additional setup. For instance, 'nvim-compe' needs explicit configuration in your init.vim. Always keep plugins updated—many autocomplete issues are fixed in newer versions.

As a developer who relies heavily on Vim's autocomplete, I've faced this issue multiple times. The problem often lies in plugin conflicts or misconfigurations. Start by verifying your plugin setup. If you're using 'dein.vim' or 'vim-plug', ensure the autocomplete plugin is loaded. For 'YouCompleteMe', run ':YcmDebugInfo' to see if it's functioning. Sometimes, the issue is with the Python interpreter—'YouCompleteMe' requires Python 3 support. Run ':echo has('python3')' to check. If it returns 0, you need to reinstall Vim with Python 3 support.
Another angle is the language server. Modern autocomplete plugins like 'coc.nvim' depend on LSP servers. If the server isn't running, autocomplete won't work. Run ':CocCommand workspace.showOutput' to see server logs. For 'coc.nvim', ensure you've installed the correct language server, like 'coc-pyright' for Python. Also, check your vimrc for conflicting mappings. Some keybindings might override autocomplete triggers. Use ':verbose imap ' to see what '' is mapped to.
If you're using 'supertab', ensure it's configured to use the correct completion source. Add 'let g:SuperTabDefaultCompletionType = \"\"' to your vimrc. Lastly, test in a minimal Vim environment with 'vim -u NONE' to rule out conflicts. Gradually add plugins back to identify the culprit.

I've been using Vim for years, and autocomplete issues can be frustrating. The first thing I check is whether the plugin manager is set up correctly. If you're using Vim-plug, ensure the plugins are installed with ':PlugInstall'. Sometimes, the issue is with the filetype—autocomplete might not trigger if Vim doesn't recognize the file type. Run ':set filetype?' to check. If it's wrong, manually set it with ':set filetype=python' (or your language). Another common culprit is the omnifunc setting. Try ':set omnifunc?' to see if it's set. If not, install a language-specific plugin like 'YouCompleteMe' or 'coc.nvim' to handle autocomplete properly.
Also, check if the autocomplete feature is enabled in your vimrc. Some plugins require explicit activation. For instance, 'YouCompleteMe' needs 'let g:ycm_auto_trigger = 1'. If you're using 'coc.nvim', ensure the language server is installed and running. Run ':CocInfo' to verify. Lastly, outdated plugins can break functionality. Regularly update them with ':PlugUpdate' or your plugin manager's equivalent.