vim: how to customize context sensitive autocomplete?

Question

For example, for any file that ends in .foo, I would like the following behavior in vim:

• if the user types i., I want vim's autocomplete to provide the list dogs, cats, mice
• if the user types i.dogs., I want vim's autocomplete to provide the list poodle,dachshund,pitbull

fwiw, I need to use this functionality in a customized language for easy typing/learning.

Answer 1

You can write a custom insert-mode completion via 'omnifunc' or 'completefunc'. Read up on the details at :help complete-functions; there are also examples.

Vim uses filetypes (e.g. java, c, markdown) as a abstraction over file extensions, which are only one way to represent the type of file (others are e.g. the #!/bin/bash hashbang lines at the top of an executable script). You can write a custom filetype detection, like this:

:autocmd BufNewFile,BufRead *.foo setf foo

And then put your custom completion in ~/.vim/ftplugin/foo_completion.vim with contents like this:

:setlocal completefunc=FooCompletion

I hope these pointers help; please refer to the help and existing filetypes for the details.