hunks: add support for gitsigns.nvim

Refactor s:get_hunks_coc() so that parsing the hunk status can be reused
by s:get_hunks_gitsigns().

Reorder s:get_hunks_coc() for consistent ordering with related code.

Give gitsigns.nvim priority over coc-git when selecting b:source_func in
hunks#get_raw_hunks().

README.md

@@ -163,7 +163,7 @@ vim-airline integrates with a variety of plugins out of the box.  These extensio
 #### [syntastic][5]
 ![image](https://f.cloud.github.com/assets/306502/962864/9824c484-04f7-11e3-9928-da94f8c7da5a.png)
 
-#### hunks ([vim-gitgutter][29] & [vim-signify][30] & [coc-git][59])
+#### hunks ([vim-gitgutter][29], [vim-signify][30], [coc-git][59] & [gitsigns.nvim][63])
 ![image](https://f.cloud.github.com/assets/306502/995185/73fc7054-09b9-11e3-9d45-618406c6ed98.png)
 
 #### [vimagit][50]
@@ -369,3 +369,4 @@ If you are interested in becoming a maintainer (we always welcome more maintaine
 [60]: https://github.com/cdelledonne/vim-cmake
 [61]: http://github.com/lambdalisue/battery.vim/
 [62]: http://github.com/rbong/vim-flog/
+[63]: https://github.com/lewis6991/gitsigns.nvim

autoload/airline/extensions.vim

@@ -234,6 +234,7 @@ function! airline#extensions#load()
         \ || exists('g:loaded_gitgutter')
         \ || exists('g:loaded_changes')
         \ || exists('g:loaded_quickfixsigns')
+        \ || exists(':Gitsigns')
         \ || exists(':CocCommand'))
     call airline#extensions#hunks#init(s:ext)
     call add(s:loaded_ext, 'hunks')

autoload/airline/extensions/hunks.vim

@@ -1,5 +1,6 @@
 " MIT License. Copyright (c) 2013-2021 Bailey Ling et al.
-" Plugin: vim-gitgutter, vim-signify, changesPlugin, quickfixsigns, coc-git
+" Plugin: vim-gitgutter, vim-signify, changesPlugin, quickfixsigns, coc-git,
+"         gitsigns.nvim
 " vim: et ts=2 sts=2 sw=2
 
 scriptencoding utf-8
@@ -8,6 +9,7 @@ if !get(g:, 'loaded_signify', 0)
   \ && !get(g:, 'loaded_gitgutter', 0)
   \ && !get(g:, 'loaded_changes', 0)
   \ && !get(g:, 'loaded_quickfixsigns', 0)
+  \ && !exists(':Gitsigns')
   \ && !exists("*CocAction")
   finish
 endif
@@ -26,21 +28,12 @@ function! s:coc_git_enabled() abort
   return 1
 endfunction
 
-function! s:get_hunks_signify() abort
-  let hunks = sy#repo#get_stats()
-  if hunks[0] >= 0
-    return hunks
-  endif
-  return []
-endfunction
-
-function! s:get_hunks_coc() abort
-  let hunks = get(b:, 'coc_git_status', '')
-  if empty(hunks)
+function! s:parse_hunk_status(hunks) abort
+  if empty(a:hunks)
     return []
   endif
   let result = [0, 0, 0]
-  for val in split(hunks)
+  for val in split(a:hunks)
     if val[0] is# '+'
      let result[0] = val[1:] + 0
     elseif val[0] is# '~'
@@ -52,6 +45,14 @@ function! s:get_hunks_coc() abort
   return result
 endfunction
 
+function! s:get_hunks_signify() abort
+  let hunks = sy#repo#get_stats()
+  if hunks[0] >= 0
+    return hunks
+  endif
+  return []
+endfunction
+
 function! s:get_hunks_gitgutter() abort
   let hunks = GitGutterGetHunkSummary()
   return hunks == [0, 0, 0] ? [] : hunks
@@ -62,6 +63,16 @@ function! s:get_hunks_changes() abort
   return hunks == [0, 0, 0] ? [] : hunks
 endfunction
 
+function! s:get_hunks_gitsigns() abort
+  let hunks = get(b:, 'gitsigns_status', '')
+  return s:parse_hunk_status(hunks)
+endfunction
+
+function! s:get_hunks_coc() abort
+  let hunks = get(b:, 'coc_git_status', '')
+  return s:parse_hunk_status(hunks)
+endfunction
+
 function! s:get_hunks_empty() abort
   return ''
 endfunction
@@ -76,6 +87,8 @@ function! airline#extensions#hunks#get_raw_hunks() abort
       let b:source_func = 's:get_hunks_changes'
     elseif exists('*quickfixsigns#vcsdiff#GetHunkSummary')
       let b:source_func = 'quickfixsigns#vcsdiff#GetHunkSummary'
+    elseif exists(':Gitsigns')
+      let b:source_func = 's:get_hunks_gitsigns'
     elseif s:coc_git_enabled()
       let b:source_func = 's:get_hunks_coc'
     else
@@ -97,6 +110,7 @@ function! airline#extensions#hunks#get_hunks() abort
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_gitgutter' &&
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_empty' &&
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_changes' &&
+    \ get(b:, 'source_func', '') isnot# 's:get_hunks_gitsigns' &&
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_coc'
     return b:airline_hunks
   endif

doc/airline.txt

@@ -838,6 +838,7 @@ vim-signify <https://github.com/mhinz/vim-signify>
 changesPlugin <https://github.com/chrisbra/changesPlugin>
 quickfixsigns <https://github.com/tomtom/quickfixsigns_vim>
 coc-git <https://github.com/neoclide/coc-git>
+gitsigns.nvim <https://github.com/lewis6991/gitsigns.nvim>
 
 You can use `airline#extensions#hunks#get_raw_hunks()` to get the full hunks,
 without shortening. This allows for advanced customization, or a quick way of