Is there a way to make use of two custom, complete functions in Vimscript?

There is sufficient information passed to completion function through its arguments. Knowing current cursor position in the command line to be completed, it is possible to determine the number of the argument that is currently being edited. Here is the function that returns that number as the only completion suggestion:

" Custom completion function for the command 'Foo'
function! FooComplete(arg, line, pos)
    let l = split(a:line[:a:pos-1], '\%(\%(\%(^\|[^\\]\)\\\)\@<!\s\)\+', 1)
    let n = len(l) - index(l, 'Foo') - 1
    return [string(n)]
endfunction

Substitute the last line with a call to one of the functions completing specific argument (assuming they are already written). For instance:

    let funcs = ['FooCompleteFirst', 'FooCompleteSecond']
    return call(funcs[n], [a:arg, a:line, a:pos])

Note that it is necessary to ignore whitespace-separated words before the command name, because those could be the limits of a range, or a count, if the command has either of them (spaces are allowed in both).

The regular expression used to split command line into arguments takes into account escaped whitespace which is a part of an argument, and not a separator. (Of course, completion functions should escape whitespace in suggested candidates, as usual in case of the command having more than one possible argument.)


There's no built-in way for vim to do this. What I'd do in this situation is embed the logic into the completion function. When you set -complete=customlist,CompletionFunction, the specified function is invoked with three arguments, in this order:

  • The current argument
  • The entire command line up to this point
  • The cursor position

So, you can analyze these and call another function depending on whether it looks like you're on the second parameter. Here's an example:

command! -nargs=* -complete=customlist,FooComplete Foo call Foo(<f-args>)
function! Foo(...)
  " ...
endfunction

function! FooComplete(current_arg, command_line, cursor_position)
  " split by whitespace to get the separate components:
  let parts = split(a:command_line, '\s\+')

  if len(parts) > 2
    " then we're definitely finished with the first argument:
    return SecondCompletion(a:current_arg)
  elseif len(parts) > 1 && a:current_arg =~ '^\s*$'
    " then we've entered the first argument, but the current one is still blank:
    return SecondCompletion(a:current_arg)
  else
    " we're still on the first argument:
    return FirstCompletion(a:current_arg)
  endif
endfunction

function! FirstCompletion(arg)
  " ...
endfunction

function! SecondCompletion(arg)
  " ...
endfunction

One problem with this example is that it would fail for completions that contain whitespace, so if that's a possibility, you're going to have to make more careful checks.

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