#333 Remember the IDs for highlights

autoload/ale/highlight.vim

@@ -22,12 +22,16 @@ function! ale#highlight#UnqueueHighlights(buffer) abort
     endif
 endfunction
 
-function! s:RemoveOldHighlights() abort
+function! s:GetALEMatches() abort
+    let l:list = []
+
     for l:match in getmatches()
         if l:match['group'] ==# 'ALEError' || l:match['group'] ==# 'ALEWarning'
-            call matchdelete(l:match['id'])
+            call add(l:list, l:match)
         endif
     endfor
+
+    return l:list
 endfunction
 
 function! ale#highlight#UpdateHighlights() abort
@@ -36,7 +40,9 @@ function! ale#highlight#UpdateHighlights() abort
     let l:loclist = l:has_new_items ? remove(s:buffer_highlights, l:buffer) : []
 
     if l:has_new_items || !g:ale_enabled
-        call s:RemoveOldHighlights()
+        for l:match in s:GetALEMatches()
+            call matchdelete(l:match['id'])
+        endfor
     endif
 
     if l:has_new_items
@@ -46,7 +52,10 @@ function! ale#highlight#UpdateHighlights() abort
             let l:line = l:item.lnum
             let l:size = 1
 
-            call matchaddpos(l:group, [[l:line, l:col, l:size]])
+            " Rememeber the match ID for the item.
+            " This ID will be used to preserve loclist items which are set
+            " many times.
+            let l:item.match_id = matchaddpos(l:group, [[l:line, l:col, l:size]])
         endfor
     endif
 endfunction
@@ -64,7 +73,7 @@ function! ale#highlight#SetHighlights(buffer, loclist) abort
         "
         " We'll filter the loclist down to items we can set now.
         let s:buffer_highlights[a:buffer] = filter(
-        \   deepcopy(a:loclist),
+        \   copy(a:loclist),
         \   'v:val.bufnr == a:buffer && v:val.col > 0'
         \)
 

autoload/ale/sign.vim

@@ -125,8 +125,7 @@ function! ale#sign#SetSigns(buffer, loclist) abort
         \   : 'ALEWarningSign'
 
         " Save the sign IDs we are setting back on our loclist objects.
-        " These IDs can be used later for changing line numbers of items
-        " we keep, based on what Vim adjusts automatically.
+        " These IDs will be used to preserve items which are set many times.
         for l:obj in l:sublist
             let l:obj.sign_id = l:sign_id
         endfor