fix branch detection

autoload/airline.vim

@@ -143,7 +143,6 @@ function! airline#update_statusline()
   endfor
 endfunction
 
-let g:airline_current_mode_text = ''
 function! airline#update_highlight()
   if get(w:, 'airline_active', 1)
     let l:m = mode()

autoload/airline/extensions/branch.vim

@@ -1,14 +1,15 @@
 " MIT license. Copyright (c) 2013 Bailey Ling.
 " vim: ts=2 sts=2 sw=2 fdm=indent
 
-function! airline#extensions#branch#init(ext)
-  if g:airline_section_b == ''
-    let g:airline_section_b =
-          \ exists('*fugitive#head') && strlen(fugitive#head()) > 0
+function! airline#extensions#branch#apply()
+  let g:airline_current_branch = exists('*fugitive#head') && strlen(fugitive#head()) > 0
         \ ? g:airline_branch_prefix.fugitive#head()
         \ : exists('*lawrencium#statusline') && strlen(lawrencium#statusline()) > 0
           \ ? g:airline_branch_prefix.lawrencium#statusline()
           \ : ''
-  endif
+endfunction
+
+function! airline#extensions#branch#init(ext)
+  call a:ext.add_statusline_funcref(function('airline#extensions#branch#apply'))
 endfunction
 

plugin/airline.vim

@@ -48,8 +48,8 @@ call s:check_defined('g:airline_mode_map', {
       \ '' : 'V-BLOCK',
       \ })
 
-call s:check_defined('g:airline_section_a', '%{g:airline_current_mode_text}')
-call s:check_defined('g:airline_section_b', '')
+call s:check_defined('g:airline_section_a', '%{get(g:, "airline_current_mode_text", "")}')
+call s:check_defined('g:airline_section_b', '%{get(g:, "airline_current_branch", "")}')
 call s:check_defined('g:airline_section_c', '%f%m')
 call s:check_defined('g:airline_section_gutter', '')
 call s:check_defined('g:airline_section_x', "%{strlen(&filetype)>0?&filetype:''}")