Fix #171 - Implement basic error highlighting

autoload/ale/cleanup.vim

@@ -10,6 +10,11 @@ function! ale#cleanup#Buffer(buffer) abort
             call ale#engine#ClearJob(l:job)
         endfor
 
+        " Clear delayed highlights for a buffer being removed.
+        if g:ale_set_highlights
+            call ale#highlight#UnqueueHighlights(a:buffer)
+        endif
+
         call remove(g:ale_buffer_info, a:buffer)
     endif
 endfunction

autoload/ale/engine.vim

@@ -234,9 +234,6 @@ function! s:HandleExit(job) abort
 
     " Call user autocommands. This allows users to hook into ALE's lint cycle.
     silent doautocmd User ALELint
-
-    " Mark line 200, column 17 with a squiggly line or something
-    " matchadd('ALEError', '\%200l\%17v')
 endfunction
 
 function! ale#engine#SetResults(buffer, loclist) abort
@@ -252,6 +249,10 @@ function! ale#engine#SetResults(buffer, loclist) abort
         " Don't load/run if not already loaded.
         call ale#statusline#Update(a:buffer, a:loclist)
     endif
+
+    if g:ale_set_highlights
+        call ale#highlight#SetHighlights(a:buffer, a:loclist)
+    endif
 endfunction
 
 function! s:HandleExitNeoVim(job, data, event) abort

autoload/ale/highlight.vim

@@ -0,0 +1,75 @@
+scriptencoding utf8
+" Author: w0rp <devw0rp@gmail.com>
+" Description: This module implements error/warning highlighting.
+
+if !hlexists('ALEError')
+    highlight link ALEError SpellBad
+endif
+
+if !hlexists('ALEWarning')
+    highlight link ALEWarning SpellCap
+endif
+
+" This map holds highlights to be set when buffers are opened.
+" We can only set highlights for whatever the current buffer is, so we will
+" wait until the buffer is entered again to show the highlights, unless
+" the buffer is in focus when linting completes.
+let s:buffer_highlights = {}
+
+function! ale#highlight#UnqueueHighlights(buffer) abort
+    if has_key(s:buffer_highlights, a:buffer)
+        call remove(s:buffer_highlights, a:buffer)
+    endif
+endfunction
+
+function! s:RemoveOldHighlights() abort
+    for l:match in getmatches()
+        if l:match['group'] ==# 'ALEError' || l:match['group'] ==# 'ALEWarning'
+            call matchdelete(l:match['id'])
+        endif
+    endfor
+endfunction
+
+function! ale#highlight#UpdateHighlights() abort
+    let l:buffer = bufnr('%')
+    let l:has_new_items = has_key(s:buffer_highlights, l:buffer)
+    let l:loclist = l:has_new_items ? remove(s:buffer_highlights, l:buffer) : []
+
+    if l:has_new_items || !g:ale_enabled
+        call s:RemoveOldHighlights()
+    endif
+
+    if l:has_new_items
+        for l:item in l:loclist
+            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
+
+            call matchaddpos(l:group, [[l:line, l:col, l:size]])
+        endfor
+    endif
+endfunction
+
+augroup ALEHighlightBufferGroup
+    autocmd!
+    autocmd BufEnter * call ale#highlight#UpdateHighlights()
+augroup END
+
+function! ale#highlight#SetHighlights(buffer, loclist) abort
+    " Only set set items for the buffer if ALE is enabled.
+    if g:ale_enabled
+        " Set a list of items to be set as highlights for a buffer when
+        " we next open it.
+        "
+        " We'll filter the loclist down to items we can set now.
+        let s:buffer_highlights[a:buffer] = filter(
+        \   a:loclist,
+        \   'v:val.bufnr == a:buffer && v:val.col > 0'
+        \)
+
+        " Update highlights for the current buffer, which may or may not
+        " be the buffer we just set highlights for.
+        call ale#highlight#UpdateHighlights()
+    endif
+endfunction

autoload/ale/sign.vim

@@ -12,14 +12,6 @@ if !hlexists('ALEWarningSign')
     highlight link ALEWarningSign todo
 endif
 
-if !hlexists('ALEError')
-    highlight link ALEError SpellBad
-endif
-
-if !hlexists('ALEWarning')
-    highlight link ALEWarning SpellCap
-endif
-
 " Signs show up on the left for error markers.
 execute 'sign define ALEErrorSign text=' . g:ale_sign_error
 \   . ' texthl=ALEErrorSign'