#538 Suport highlight sizes by looking at end column numbers

autoload/ale/engine.vim

@@ -288,6 +288,11 @@ function! ale#engine#FixLocList(buffer, linter, loclist) abort
             let l:item.detail = l:old_item.detail
         endif
 
+        " Pass on a col_length key if set, used for highlights.
+        if has_key(l:old_item, 'end_col')
+            let l:item.end_col = str2nr(l:old_item.end_col)
+        endif
+
         if l:item.lnum == 0
             " When errors appear at line 0, put them at line 1 instead.
             let l:item.lnum = 1

autoload/ale/highlight.vim

@@ -86,7 +86,7 @@ function! ale#highlight#UpdateHighlights() abort
             let l:col = l:item.col
             let l:group = l:item.type ==# 'E' ? 'ALEError' : 'ALEWarning'
             let l:line = l:item.lnum
-            let l:size = 1
+            let l:size = has_key(l:item, 'end_col') ? l:item.end_col - l:col : 1
 
             " Rememeber the match ID for the item.
             " This ID will be used to preserve loclist items which are set