queue :syn and :hi commands during parse

This means only a single :exe is run per frame for all highlighting-
related commands, which *drastically* speeds up processing for frames
with a very large number of newly encountered colors in the viewport.
The magnitude of improvement is enough to make opening or paging through
the torture test CSS file nearly tolerable (or maybe better put, reduces
lag to almost purely the sluggishness of Vim’s own repaint).

Author: ap

autoload/css_color.vim

@@ -43,9 +43,14 @@ for i in range(0, 255)
 	let s:hex[ printf( '%02x', i ) ] = i
 endfor
 
+let s:exe=[]
+function! s:flush_exe()
+	if len(s:exe) | exe join( remove( s:exe, 0, -1 ), ' | ' ) | endif
+endfunction
+
 if has('gui_running')
 	function! s:create_highlight(color, is_bright)
-		exe 'hi BG'.a:color 'guibg=#'.a:color 'guifg=#'.( a:is_bright ? '000000' : 'ffffff' )
+		call add( s:exe, 'hi BG'.a:color.' guibg=#'.a:color.' guifg=#'.( a:is_bright ? '000000' : 'ffffff' ) )
 	endfunction
 else
 	" preset 16 vt100 colors
@@ -121,8 +126,11 @@ else
 			let color_idx = s:rgb2xterm(a:color)
 			let s:color_idx[a:color] = color_idx
 		endif
-		exe 'hi BG'.a:color 'ctermbg='.color_idx 'ctermfg='.( a:is_bright ? 0 : 15 )
-		\                    'guibg=#'.a:color    'guifg=#'.( a:is_bright ? '000000' : 'ffffff' )
+		call add( s:exe,
+			\   'hi BG'.a:color
+			\ . ' guibg=#' .a:color  .' guifg=#' .( a:is_bright ? '000000' : 'ffffff' )
+			\ . ' ctermbg='.color_idx.' ctermfg='.( a:is_bright ? 0 : 15 )
+			\ )
 	endfunction
 endif
 
@@ -168,7 +176,7 @@ function! s:create_syn_match()
 
 	" iff pattern ends on word character, require word break to match
 	if pattern =~ '\>$' | let pattern .= '\>' | endif
-	exe 'syn match BG'.rgb_color.' /'.escape(pattern, '/').'/ contained containedin=@colorableGroup'
+	call add( s:exe, 'syn match BG'.rgb_color.' /'.escape(pattern, '/').'/ contained containedin=@colorableGroup' )
 
 	return ''
 endfunction
@@ -219,12 +227,14 @@ function! s:parse_screen()
 	let left = max([ leftcol - 15, 0 ])
 	let width = &columns * 4
 	call filter( range( line('w0'), line('w$') ), 'substitute( strpart( getline(v:val), col([v:val, left]), width ), b:css_color_pat, ''\=s:create_syn_match()'', ''g'' )' )
+	call s:flush_exe()
 endfunction
 
 """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
 
 function! css_color#reinit()
 	call filter( keys( b:css_color_hi ), 's:create_highlight( v:val, s:color_bright[v:val] )' )
+	call s:flush_exe()
 endfunction
 
 function! css_color#enable()