support vim-signify as a hunk source.

README.md

@@ -7,7 +7,7 @@ Lean & mean statusline for vim that's light as air.
 # Features
 
 *  tiny core written with extensibility in mind ([open/closed principle][8]).
-*  integrates with a variety of plugins, including: [vim-bufferline][6], [fugitive][4], [unite][9], [ctrlp][10], [minibufexpl][15], [gundo][16], [undotree][17], [nerdtree][18], [tagbar][19], [vim-gitgutter][29], [syntastic][5] and [lawrencium][21].
+*  integrates with a variety of plugins, including: [vim-bufferline][6], [fugitive][4], [unite][9], [ctrlp][10], [minibufexpl][15], [gundo][16], [undotree][17], [nerdtree][18], [tagbar][19], [vim-gitgutter][29], [vim-signify][30], [syntastic][5] and [lawrencium][21].
 *  looks good with regular fonts and provides configuration points so you can use unicode or powerline symbols.
 *  optimized for speed; it loads in under a millisecond.
 *  fully customizable; if you know a little `statusline` syntax you can tweak it to your needs.
@@ -136,3 +136,4 @@ MIT license. Copyright (c) 2013 Bailey Ling.
 [27]: https://github.com/bling/vim-airline/wiki/FAQ
 [28]: https://github.com/chrisbra/csv.vim
 [29]: https://github.com/airblade/vim-gitgutter
+[30]: https://github.com/mhinz/vim-signify

autoload/airline/extensions.vim

@@ -129,7 +129,7 @@ function! airline#extensions#load()
   endif
 
   if (get(g:, 'airline#extensions#hunks#enabled', 1) && get(g:, 'airline_enable_hunks', 1))
-        \ && exists('*GitGutterGetHunkSummary')
+        \ && (exists('g:loaded_signify') || exists('g:loaded_gitgutter'))
     call airline#extensions#hunks#init(s:ext)
   endif
 

autoload/airline/extensions/hunks.vim

@@ -4,11 +4,34 @@
 let s:non_zero_only = get(g:, 'airline#extensions#hunks#non_zero_only', 0)
 let s:hunk_symbols = get(g:, 'airline#extensions#hunks#hunk_symbols', ['+', '~', '-'])
 
-function! airline#extensions#hunks#get_hunks()
-  if get(g:, 'gitgutter_enabled', 0) == 0
-    return ''
+let s:initialized = 0
+function! s:init()
+  if !s:initialized
+    let s:initialized = 1
+    if exists('*sy#repo#get_stats')
+      function! s:get_hunks()
+        let hunks = sy#repo#get_stats()
+        return hunks
+      endfunction
+    elseif exists('*GitGutterGetHunkSummary')
+      function! s:get_hunks()
+        if !get(g:, 'gitgutter_enabled', 0)
+          return ''
+        endif
+        return GitGutterGetHunkSummary()
+      endfunction
+    else
+      let s:non_zero_only = 1
+      function! s:get_hunks()
+        return [0, 0, 0]
+      endfunction
+    endif
   endif
-  let hunks = GitGutterGetHunkSummary()
+endfunction
+
+function! airline#extensions#hunks#get_hunks()
+  call <sid>init()
+  let hunks = s:get_hunks()
   let string = ''
   for i in [0, 1, 2]
     if s:non_zero_only == 0 || hunks[i] > 0

doc/airline.txt

@@ -203,8 +203,9 @@ csv.vim <https://github.com/chrisbra/csv.vim>
 <
                                                              *airline-hunks*
 vim-gitgutter <https://github.com/airblade/vim-gitgutter>
+vim-signify <https://github.com/mhinz/vim-signify>
 
-* enable/disable detecting changed hunks under source control. >
+* enable/disable showing a summary of changed hunks under source control.
   let g:airline#extensions#hunks#enabled = 1
 <
 * enable/disable showing only non-zero hunks. >