config: allow to disable setting the statusline option

closes #2013

autoload/airline.vim

@@ -125,7 +125,7 @@ endfunction
 
 " Update the statusline
 function! airline#update_statusline()
-  if airline#util#getwinvar(winnr(), 'airline_disabled', 0)
+  if airline#util#stl_disabled()
     return
   endif
   let range = filter(range(1, winnr('$')), 'v:val != winnr()')
@@ -154,7 +154,7 @@ endfunction
 
 " Function to draw inactive statuslines for inactive windows
 function! airline#update_statusline_inactive(range)
-  if airline#util#getwinvar(winnr(), 'airline_disabled', 0)
+  if airline#util#stl_disabled()
     return
   endif
   for nr in a:range

autoload/airline/util.vim

@@ -161,3 +161,12 @@ function! airline#util#themes(match)
   let files = split(globpath(&rtp, 'autoload/airline/themes/'.a:match.'*.vim'), "\n")
   return sort(map(files, 'fnamemodify(v:val, ":t:r")') + ['random'])
 endfunction
+
+function! airline#util#stl_disabled()
+  " setting the statusline is disabled,
+  " either globally or per window
+  " w:airline_disabled is deprecated!
+  return get(g:, 'airline_disable_statusline', 0) ||
+   \ airline#util#getwinvar(winnr(), 'airline_disable_statusline', 0) ||
+   \ airline#util#getwinvar(winnr(), 'airline_disabled', 0)
+endfunction

doc/airline.txt

@@ -228,10 +228,19 @@ values):
   heavily) >
   let g:airline_exclude_preview = 0
 <
-* disable the Airline customization for selected windows (this is a
+* disable the Airline statusline customization for selected windows (this is a
   window-local variable so you can disable it per-window) >
-  let w:airline_disabled = 1
+  let w:airline_disable_statusline = 1
+<
+  Old deprecated name: `w:airline_disabled`
 
+  See also the following option, for disabling setting the statusline globally
+* Disable setting the statusline option: >
+  let g:airline_disable_statusline = 1
+
+< This setting disables setting the 'statusline' option. This allows to use
+ e.g. the tabline extension (|airline-tabline|) but keep the 'statusline'
+ option totally configurable by a custom configuration.
 * Do not draw separators for empty sections (only for the active window) >
   let g:airline_skip_empty_sections = 1
 <

plugin/airline.vim

@@ -178,8 +178,10 @@ function! s:airline_toggle()
       endif
     augroup END
 
-    if &laststatus < 2
+    if !airline#util#stl_disabled()
-      set laststatus=2
+      if &laststatus < 2
+        set laststatus=2
+      endif
     endif
     if s:airline_initialized
       call s:on_window_changed('Init')