(ab)using the command message window for function signatures

signature.vim

" (ab)using the command message window for function signatures
" Barry Arthur, Oct 2015

function! Signature(msg)
  let m = filter(string#scanner(a:msg).split('.\{80}', 1), 'v:val != ""')
  let len = len(m)
  let msg = join(m, "\n")
  let old_cmdheight = &cmdheight
  let &cmdheight = len
  echo msg
  augroup Sig
    au!
    exe "au InsertLeave * let &cmdheight = " . old_cmdheight
  augroup END
endfunction

" Imagine that the following call is made at the time of completion to show the
" signature of the just-expanded function. Due to completion, you would still
" be in insert mode and ready to type... when you leave insert mode, the
" signature is cleared.
call Signature("once a jolly swagman camped by a billabong under the shade of a coolabah tree when down came a jumbuck to drink at that waterhole and up jumped the swagman and grabbed him with glee and he sang you'll come a-waltzing matilda with me oh! waltzing matilda! waltzing matilda! you'll come a-waltzing matilda with me")
$
startinsert
finish