add ability to override left/right sides independently

autoload/airline.vim

@@ -79,7 +79,7 @@ function! s:get_statusline(winnr, active)
   let l:file_flag_color = a:active ? "%#Al7#" : "%#Al7_inactive#"
 
   let sl = '%{airline#update_highlight()}'
-  if a:active || s:getwinvar(a:winnr, 'airline_left_only', 0)
+  if s:getwinvar(a:winnr, 'airline_render_left', a:active)
     let sl.=l:mode_color.s:get_section(a:winnr, 'a')
     let sl.='%{g:airline_detect_paste && &paste ? g:airline_paste_symbol." " : ""}'
     let sl.=l:mode_sep_color
@@ -95,7 +95,7 @@ function! s:get_statusline(winnr, active)
   else
     let sl.=l:status_color.' %f%m'
   endif
-  if !s:getwinvar(a:winnr, 'airline_left_only', 0)
+  if s:getwinvar(a:winnr, 'airline_render_right', 1)
     let sl.='%='
     let sl.=s:get_section(a:winnr, 'x')
     let sl.=l:info_sep_color
@@ -146,7 +146,8 @@ function! airline#update_statusline()
 
   let w:airline_active = 1
 
-  unlet! w:airline_left_only
+  unlet! w:airline_render_left
+  unlet! w:airline_render_right
   for section in s:sections
     unlet! w:airline_section_{section}
   endfor

autoload/airline/extensions.vim

@@ -28,7 +28,8 @@ function! airline#extensions#apply_left_override(section1, section2)
   let w:airline_section_b = a:section2
   let w:airline_section_c = ''
   let w:airline_section_gutter = ' '
-  let w:airline_left_only = 1
+  let w:airline_render_left = 1
+  let w:airline_render_right = 0
 endfunction
 
 let s:active_winnr = -1
@@ -41,12 +42,10 @@ function! airline#extensions#update_statusline()
     let w:airline_section_c = ''
     let w:airline_section_x = ''
   elseif &buftype == 'help'
-    let w:airline_section_a = 'Help'
-    let w:airline_section_b = '%f'
-    let w:airline_section_c = ''
-    let w:airline_section_gutter = ' '
+    call airline#extensions#apply_left_override('Help', '%f')
     let w:airline_section_x = ''
     let w:airline_section_y = ''
+    let w:airline_render_right = 1
   endif
 
   if &previewwindow