Is it possible to have vim auto-complete function names, variables, etc. when using it to program?

Question

Many IDEs automatically complete function names, variables, method names, etc. as the user types. The best ones complete the names based both on the language's built-in library as well as what has already been defined in other files of the same program.

For example, as I'm typing the following Python program:

hungy = True

def eatFood(food):
    pass

if hungry:
    eatF

the line eatF would automatically show eatFood() as an available auto-complete option.

Does Vim have this capability? If so, how can I enable it?

Answer 1

There are many different flavors of autocomplete in vim. One way might be to use SuperTab. This provides a way to use tab-completion at more or less any time. This would enable you to hit Tab after you've partially typed the word to get a completion list. For instance, typing eatF followed by Tab to expand to eatFood.

Please Note: these pictures all link to example gifs in action.

Vim has excellent other options. You should read :h ins-completion to see the variety of built-in completion options. Using vim's Ctrl-XCtrl-O, combined with a python-aware plugin like jedi can give a completion flavor. Jedi can be configured to give documentation on omni-completion (this is what Ctrl-XCtrl-O does). Then documentation for the completion candidates would appear in a split window.

Using similar plugins but different options leads to all sorts of behaviours. It's possible, for instance, to not need to prompt for autocompletion (if that's what you're after). Instead, after you type some number of letters (say, 2 or 3) of a word, a plugin can try to intelligently offer possible completions in a menu.

So the short answer is a yes! But the configuration process can be a bit complicated. I think of it as a step in the long stairway of mastering vim.

Answer 2

Such functionality - i.e., searching the current file (and all open files) for auto-completion, should be enabled by default with Ctrl+P:

You can go to the next suggestion with Ctrl+N, the previous suggestion with Ctrl+P and select it by typing any letter (which will be appended right after the suggestion).

Answer 3

Vim has support for completion natively. You can read about the various different completions that Vim supports at :h ins-completion.

In general, for all purposes I have found, ins-completions are enough for my liking, however there are some completion plugins that add more value beyond what ins-completions offers. NeoComplete, YCM (YouCompleteMe) are a few for the same. They are more advanced in the sense that they try to combine different types of completions more accurately, and they also have advanced caching mechanisms, so they tend to be faster. YCM even goes to the extent to work with external compilers / utilities to provide better IntelliSense.

Answer 4

In insert mode, type the first couple of characters of a word, then press:

• Ctrl-N to insert the next matching word; or
• Ctrl-P to insert the previous matching word.

This is particularly useful when entering the names of variables in a program.

The 'complete' option controls where the keywords are searched (include files, tag files, buffers, and more).

The 'completeopt' option controls how the completion occurs (for example, whether a menu is shown).

For help on Ctrl-N and Ctrl-P, see :help compl-generic .

Answer 5

Yes, auto completion scripts for vim exist. The "best" choice is depending on your programming language. As your example code is Python I suggest to take a look at Jedi. Build on top of that You complete me exists, which also has support for other languages, but is sometimes seen as too big. For other languages you can browse through the long set on vim scripts.

Answer 6

CoC, the Conqueror of Completion also deserves a mention. It is very advanced, comparable to VSCode's Intellisense, with extensions tailored to each language. It works with Vim 8 and with Neovim.

If you are not using a plugin manager, then the initial setup may take a little effort: You will need node installed, then run npm run build in CoC's home folder to get it ready.

After installing, you just need to tell CoC which languages you like to use. For example:

:CocInstall coc-tsserver coc-json coc-html coc-css

:CocInstall coc-python coc-perl

You can find a list here or a list with options here.

After that you are ready to go!

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There is also a lot of optional configuration you can play with. Here are some of the things I am currently trying:

    " Rename only in the current file (or maybe only in open buffers)
    nmap <leader>rr <Plug>(coc-rename)
    " Find all occurrences in project
    nnoremap <leader>prw :CocSearch <C-R>=expand("<cword>")<CR><CR>

    " The following are just some of the suggested settings from CoC's README.md {{{

    set shortmess+=c

    " Use `[g` and `]g` to navigate diagnostics
    " Use `:CocDiagnostics` to get all diagnostics of current buffer in location list.
    nmap <silent> [g <Plug>(coc-diagnostic-prev)
    nmap <silent> ]g <Plug>(coc-diagnostic-next)

    " GoTo code navigation.
    nmap <silent> gd <Plug>(coc-definition)
    nmap <silent> gy <Plug>(coc-type-definition)
    nmap <silent> gi <Plug>(coc-implementation)
    nmap <silent> gr <Plug>(coc-references)

    " Use K to show documentation in preview window.
    nnoremap <silent> gh :call <SID>show_documentation()<CR>    

    function! s:show_documentation()
        if (index(['vim','help'], &filetype) >= 0)
            execute 'h '.expand('<cword>')
        else
            call CocAction('doHover')
        endif
    endfunction

    " Highlight the symbol and its references when holding the cursor.
    autocmd CursorHold * silent call CocActionAsync('highlight')

    " Symbol renaming.
    nmap <leader>rn <Plug>(coc-rename)

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I got interested in CoC after a friend shared this video:

• Vim [project-wide] Search and Replace - The Primagen

Having said that, The Primagen seems to prefer using the Neovim LSP these days.