highlight: skip processing the same hi group twice

Shouldn't happen, but just in case skip creating highlighting group,
if the same group with the same attributes has already been defined.

autoload/airline.vim

@@ -47,7 +47,9 @@ function! airline#load_theme()
   endif
 
   call airline#highlighter#load_theme()
+  let g:airline_theme_dict = {}
   call airline#extensions#load_theme()
+  unlet g:airline_theme_dict
   call airline#update_statusline()
 endfunction
 
@@ -102,6 +104,7 @@ function! airline#update_statusline()
   if airline#util#getwinvar(winnr(), 'airline_disabled', 0)
     return
   endif
+  let g:airline_theme_dict={}
   for nr in filter(range(1, winnr('$')), 'v:val != winnr()')
     if airline#util#getwinvar(nr, 'airline_disabled', 0)
       continue
@@ -117,6 +120,7 @@ function! airline#update_statusline()
   let w:airline_active = 1
   let context = { 'winnr': winnr(), 'active': 1, 'bufnr': winbufnr(winnr()) }
   call s:invoke_funcrefs(context, g:airline_statusline_funcrefs)
+  unlet g:airline_theme_dict
 endfunction
 
 let s:contexts = {}
@@ -198,9 +202,11 @@ function! airline#check_mode(winnr)
     return ''
   endif
   if get(w:, 'airline_lastmode', '') != mode_string
+    let g:airline_theme_dict = {}
     call airline#highlighter#highlight_modified_inactive(context.bufnr)
     call airline#highlighter#highlight(l:mode, context.bufnr)
     let w:airline_lastmode = mode_string
+    unlet g:airline_theme_dict
   endif
 
   return ''

autoload/airline/extensions/tabline.vim

@@ -118,13 +118,18 @@ function! airline#extensions#tabline#get()
   if !exists('#airline#BufAdd#*')
     autocmd airline BufAdd * call <sid>update_tabline()
   endif
-  if s:ctrlspace
-    return airline#extensions#tabline#ctrlspace#get()
-  elseif s:show_buffers && curtabcnt == 1 || !s:show_tabs
-    return airline#extensions#tabline#buffers#get()
-  else
-    return airline#extensions#tabline#tabs#get()
-  endif
+  try
+    let g:airline_theme_dict = {}
+    if s:ctrlspace
+      return airline#extensions#tabline#ctrlspace#get()
+    elseif s:show_buffers && curtabcnt == 1 || !s:show_tabs
+      return airline#extensions#tabline#buffers#get()
+    else
+      return airline#extensions#tabline#tabs#get()
+    endif
+  finally
+    unlet g:airline_theme_dict
+  endtry
 endfunction
 
 function! airline#extensions#tabline#title(n)

autoload/airline/highlighter.vim

@@ -84,6 +84,10 @@ function! airline#highlighter#exec(group, colors)
   if len(colors) == 4
     call add(colors, '')
   endif
+  if has_key(g:airline_theme_dict, 'a:group') &&
+        \ get(g:airline_theme_dict[a:group]) == a:colors
+    return
+  endif
   if g:airline_gui_mode ==# 'gui'
     let new_hi = [colors[0], colors[1], '', '', colors[4]]
   else
@@ -98,6 +102,7 @@ function! airline#highlighter#exec(group, colors)
         \ s:Get(colors, 4, 'term=', ''))
     exe cmd
   endif
+  let g:airline_theme_dict[a:group] = a:colors
 endfunction
 
 function! s:CheckDefined(colors)
@@ -160,6 +165,7 @@ function! airline#highlighter#load_theme()
   if pumvisible()
     return
   endif
+  let g:airline_theme_dict = {}
   for winnr in filter(range(1, winnr('$')), 'v:val != winnr()')
     call airline#highlighter#highlight_modified_inactive(winbufnr(winnr))
   endfor
@@ -169,6 +175,7 @@ function! airline#highlighter#load_theme()
   else
     call airline#highlighter#highlight(['normal'])
   endif
+  unlet g:airline_theme_dict
 endfunction
 
 function! airline#highlighter#add_separator(from, to, inverse)