Augment fzf#complete interface with reducer option

README.md

@@ -48,8 +48,7 @@ List of commands
   bindings to open in a new tab, a new split, or in a new vertical split.
 - Bang-versions of the commands (e.g. `Ag!`) will open fzf in fullscreen
 
-Customization
--------------
+### Customization
 
 ```vim
 " This is the default extra key bindings
@@ -59,6 +58,35 @@ let g:fzf_action = {
   \ 'ctrl-v': 'vsplit' }
 ```
 
+Fuzzy completion helper
+-----------------------
+
+`fzf#complete` is a helper function for creating custom fuzzy completion using
+fzf. If the first parameter is a command string or a Vim list, it will be used
+as the source.
+
+```vim
+" Replace the default dictionary completion with fzf-based fuzzy completion
+inoremap <expr> <c-x><c-k> fzf#complete('cat /usr/share/dict/words')
+```
+
+For advanced uses, you can pass an options dictionary to the function. The set
+of options is almost identical to that for `fzf#run`, except that it takes
+`reducer` function instead of `sink` or `sink*`.
+
+```vim
+" Reducer function transforms the output of fzf into a single string value
+function! FirstLineInUpperCase(lines)
+  return toupper(a:lines[0])
+endfunction
+
+inoremap <expr> <c-x><c-k> fzf#complete({
+  \ 'source':  'cat /usr/share/dict/words',
+  \ 'reducer': function('FirstLineInUpperCase'),
+  \ 'options': '--no-multi --reverse --margin 15%,0',
+  \ 'left':    20})
+```
+
 License
 -------
 

plugin/fzf.vim

@@ -49,8 +49,10 @@ function! s:buflisted()
   return filter(range(1, bufnr('$')), 'buflisted(v:val)')
 endfunction
 
+let s:default_window = {'down': '40%'}
+
 function! s:fzf(opts, bang)
-  return fzf#run(extend(a:opts, a:bang ? {} : get(g:, 'fzf_window', {'down': '40%'})))
+  return fzf#run(extend(a:opts, a:bang ? {} : get(g:, 'fzf_window', s:default_window)))
 endfunction
 
 let s:default_action = {
@@ -398,19 +400,36 @@ command! -bang Commands call s:commands(<bang>0)
 inoremap <silent> <Plug>(-fzf-complete-trigger) <c-o>:call <sid>complete_trigger()<cr>
 
 function! s:complete_trigger()
-  call s:fzf({
-  \ 'source':  s:source,
-  \ 'sink':    function('s:complete_insert'),
-  \ 'options': '+m -q '.shellescape(s:query)}, 0)
+  let opts = copy(s:opts)
+  let opts.options = printf('+m -q %s %s', shellescape(s:query), get(opts, 'options', ''))
+  let opts['sink*'] = function('s:complete_insert')
+  if has_key(opts, 'reducer')
+    let s:reducer = opts.reducer
+    call remove(opts, 'reducer')
+  else
+    let s:reducer = function('s:first_line')
+  endif
+  call fzf#run(opts)
 endfunction
 
-function! s:complete_insert(data)
+" The default reducer
+function! s:first_line(lines)
+  return a:lines[0]
+endfunction
+
+function! s:complete_insert(lines)
+  if empty(a:lines)
+    return
+  endif
+
   let chars = strchars(s:query)
-  if chars == 0     | let del = ''
+  if     chars == 0 | let del = ''
   elseif chars == 1 | let del = '"_x'
   else              | let del = (chars - 1).'"_dvh'
   endif
-  execute 'normal!' (s:eol ? '' : 'h').del.(s:eol ? 'a': 'i').a:data
+
+  let data = call(s:reducer, [a:lines])
+  execute 'normal!' (s:eol ? '' : 'h').del.(s:eol ? 'a': 'i').data
   if has('nvim')
     call feedkeys('a')
   else
@@ -418,8 +437,16 @@ function! s:complete_insert(data)
   endif
 endfunction
 
-function! fzf#complete(source)
-  let s:source = a:source
+function! fzf#complete(arg)
+  if type(a:arg) == type({})
+    if has_key(a:arg, 'sink') || has_key(a:arg, 'sink*')
+      echoerr 'sink not allowed'
+      return ''
+    endif
+    let s:opts = a:arg
+  else
+    let s:opts = extend({'source': a:arg}, get(g:, 'fzf_window', s:default_window))
+  endif
 
   let eol = col('$')
   let ve = &ve