Add function to clone highlight groups with attrs

plugin/functions.vim

@@ -5,6 +5,29 @@ function! FoldText()
   return line.' '.string(v:foldend - v:foldstart + 1).' lines '
 endfunction
 
+" Derived from http://stackoverflow.com/a/1333025
+function! CloneHighlightGroupWithAttributes(group, new_group, attributes)
+  " Get group details, resolving group links.
+  redir => group
+  exe "silent hi " . a:group
+  redir END
+  while group =~ "links to"
+    let index = stridx(group, "links to") + len("links to")
+    let linked_group =  strpart(group, index + 1)
+    redir => group
+    exe "silent hi " . linked_group
+    redir END
+  endwhile
+
+  " Get highlight parameters and existing remove attributes.
+  let parameters = matchlist(group, '\<xxx\>\s\+\(.*\)')[1]
+  let parameters = substitute(parameters, '\(c\?term\|gui\)=\w\+', '', 'g')
+
+  " Create the cloned highlight group with new attributes.
+  exe 'hi '.a:new_group.' '.parameters.
+        \' term='.a:attributes.' cterm='.a:attributes.' gui='.a:attributes
+endfunction
+
 " Strip trailing whitespace
 function! <SID>StripWhitespace()
   let l = line(".")