Adjust output of `luacheck` linter to include error code (#717)

* linters/lua/luacheck: Show error code in message

ale_linters/lua/luacheck.vim

@@ -22,14 +22,14 @@ function! ale_linters#lua#luacheck#Handle(buffer, lines) abort
     "
     " artal.lua:159:17: (W111) shadowing definition of loop variable 'i' on line 106
     " artal.lua:182:7: (W213) unused loop variable 'i'
-    let l:pattern = '^.*:\(\d\+\):\(\d\+\): (\([WE]\)\d\+) \(.\+\)$'
+    let l:pattern = '^.*:\(\d\+\):\(\d\+\): (\([WE]\)\(\d\+\)) \(.\+\)$'
     let l:output = []
 
     for l:match in ale#util#GetMatches(a:lines, l:pattern)
         call add(l:output, {
         \   'lnum': l:match[1] + 0,
         \   'col': l:match[2] + 0,
-        \   'text': l:match[4],
+        \   'text': l:match[3] . l:match[4] . ': ' . l:match[5],
         \   'type': l:match[3],
         \})
     endfor

test/handler/test_lua_handler.vader

@@ -0,0 +1,32 @@
+After:
+  call ale#linter#Reset()
+
+Execute(The luacheck handler should parse lines correctly):
+  runtime ale_linters/lua/luacheck.vim
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 1,
+  \     'col': 8,
+  \     'text': 'W612: line contains trailing whitespace',
+  \     'type': 'W',
+  \   },
+  \   {
+  \     'lnum': 3,
+  \     'col': 5,
+  \     'text': 'W213: unused loop variable ''k''',
+  \     'type': 'W',
+  \   },
+  \   {
+  \     'lnum': 3,
+  \     'col': 19,
+  \     'text': 'W113: accessing undefined variable ''x''',
+  \     'type': 'W',
+  \   },
+  \ ],
+  \ ale_linters#lua#luacheck#Handle(347, [
+  \   '    /file/path/here.lua:1:8: (W612) line contains trailing whitespace',
+  \   '    /file/path/here.lua:3:5: (W213) unused loop variable ''k''',
+  \   '    /file/path/here.lua:3:19: (W113) accessing undefined variable ''x''',
+  \ ])