Use the buffers auto completion in an input() dialogue

Question

I am trying to add autocompletion, with suggestions from the currently edited buffer when reading input from the user for a search string:

function! Testinput()
    return input("Enter search string: ", 'default', 'syntax')
endfun
call Testinput()

In the above snippet, syntax is the {completion} argument, from the help:

  The optional {completion} argument specifies the type of
  completion supported for the input.  Without it completion is
  not performed.  The supported completion types are the same as
  that can be supplied to a user-defined command using the
  "-complete=" argument.  Refer to |:command-completion| for
  more information.  Example: >
      let fname = input("File: ", "", "file")

I looked though the list available :help command-completion, the closest matches I could find are: syntax, tags (error about not having ctags), i.e. neither one worked. I tested it with file and I indeed had file autocompletion.

Surely its quite a common use case to auto complete using the buffere's auto complete (or the text in the buffer)? I tried to figure out what auto complete function is currently in use and could not find it (e.g. omnifunc is set to nothing), and the help shows one how to make an autocomplete function.

Answer 1

"tags" is probably the closest built-in, if you want to complete project contents, but you'd need a tags file. There doesn't seem to be a method for buffer contents. We can write a custom one:

function! CompleteWords(ArgLead, CmdLine, ...)
  return getline(1, '$')->join(' ')->split('\s\+')
        \ ->filter({_,x->match(x, '^\h\w\+$') > -1})
        \ ->filter({_,x->match(x, '^' . a:CmdLine) > -1})
        \ ->sort()->uniq()
endfunction

call input('file: ', '', 'customlist,CompleteWords')

This function just gets the current buffer's text, and splits it word-by-word, filters to the current entered text, and then unique-sorts.

It is not efficient if your buffer is huge, but for moderate size buffers it should work.

Answer 2

I'm using Neovim if that makes a difference. @Mass's answer did not work for me until I modified it to:

function! CompleteWords(ArgLead, CmdLine, ...)
    let str = getline(1, '$')
    let str  = join(str, ' ')
    let slist = split(str, '\s\+')
    call filter(slist, {_, x -> match(x, '^\h\w\+$') > -1})
    call filter(slist, {_, x -> match(x, '^' . a:CmdLine) > -1})
    call sort(slist)
    call uniq(slist)
    return slist
endfunction
call input('file: ', '', 'customlist,CompleteWords')

Additionally it was not finding some of the matches, so I made it a bit smarter:

function! CompleteFromBufferWords(ArgLead, CmdLine, ...)
    let str = getline(1, '$')
    let str  = join(str, ' ')
    " Split on whitespace and unusual characters (excludes - and _)
    let slist = split(str, '[ \t~!@#$%^&*+=()<>{}[\];:|,.?"\\/'']\+')
    call filter(slist, {_, x -> len(x) > 2 && match(x, '^[a-zA-Z_]\+') > -1})
    " If must start with the word:
    "call filter(slist, {_, x -> match(x, '^' . a:CmdLine) > -1})
    " If must only contain the word:
    call filter(slist, {_, x -> match(x, a:CmdLine) > -1})
    call sort(slist)
    call uniq(slist)
    return slist
endfunction
call input('file: ', '', 'customlist,CompleteFromBufferWords')