main: disable airline on FocusLost

When switching away from Vim and your terminal supports the FocusLost
autocommand, set the statusline to inactive, so it won't distract you
too much when working with another application.

In the gui, the FocusLost autocommand should always trigger.

This is now the default, if people start complaining, that behaviour
should probably be made configurable.

closes #1807

autoload/airline.vim

@@ -103,14 +103,9 @@ function! airline#update_statusline()
   if airline#util#getwinvar(winnr(), 'airline_disabled', 0)
     return
   endif
-  for nr in filter(range(1, winnr('$')), 'v:val != winnr()')
-    if airline#util#getwinvar(nr, 'airline_disabled', 0)
-      continue
-    endif
-    call setwinvar(nr, 'airline_active', 0)
-    let context = { 'winnr': nr, 'active': 0, 'bufnr': winbufnr(nr) }
-    call s:invoke_funcrefs(context, s:inactive_funcrefs)
-  endfor
+  let range = filter(range(1, winnr('$')), 'v:val != winnr()')
+  " create inactive statusline
+  call airline#update_statusline_inactive(range)
 
   unlet! w:airline_render_left w:airline_render_right
   exe 'unlet! ' 'w:airline_section_'. join(s:sections, ' w:airline_section_')
@@ -120,6 +115,20 @@ function! airline#update_statusline()
   call s:invoke_funcrefs(context, g:airline_statusline_funcrefs)
 endfunction
 
+function! airline#update_statusline_inactive(range)
+  if airline#util#getwinvar(winnr(), 'airline_disabled', 0)
+    return
+  endif
+  for nr in a:range
+    if airline#util#getwinvar(nr, 'airline_disabled', 0)
+      continue
+    endif
+    call setwinvar(nr, 'airline_active', 0)
+    let context = { 'winnr': nr, 'active': 0, 'bufnr': winbufnr(nr) }
+    call s:invoke_funcrefs(context, s:inactive_funcrefs)
+  endfor
+endfunction
+
 let s:contexts = {}
 let s:core_funcrefs = [
       \ function('airline#extensions#apply'),

plugin/airline.vim

@@ -105,6 +105,8 @@ function! s:airline_toggle()
       if exists("##TerminalOpen")
         autocmd TerminalOpen * call <sid>on_colorscheme_changed()
       endif
+      " Set all statuslines to inactive
+      autocmd FocusLost * call airline#update_statusline_inactive(range(1, winnr('$')))
       " Refresh airline for :syntax off
       autocmd SourcePre */syntax/syntax.vim
             \ call airline#extensions#tabline#buffers#invalidate()
@@ -119,7 +121,7 @@ function! s:airline_toggle()
             \ |   call <sid>on_window_changed()
             \ | endif
 
-      autocmd VimResized * unlet! w:airline_lastmode | :call <sid>airline_refresh()
+      autocmd VimResized,FocusGained * unlet! w:airline_lastmode | :call <sid>airline_refresh()
       autocmd TabEnter * :unlet! w:airline_lastmode | let w:airline_active=1
       autocmd BufWritePost */autoload/airline/themes/*.vim
             \ exec 'source '.split(globpath(&rtp, 'autoload/airline/themes/'.g:airline_theme.'.vim', 1), "\n")[0]