Support older checkstyle versions

The output format used by older checkstyle versions differs from the one
of new versions. This commit adds a second parsing iteration on the
output lines with a suitable pattern to support both versions in
parallel. Due to the differences in the order of matching groups this is
hard to achieve in a single pass through the output lines.

An appropriate test case is added.

ale_linters/java/checkstyle.vim

@@ -2,9 +2,11 @@
 " Description: checkstyle for Java files
 
 function! ale_linters#java#checkstyle#Handle(buffer, lines) abort
-    let l:pattern = '\v\[(WARN|ERROR)\] [a-zA-Z]?:?[^:]+:(\d+):(\d+)?:? (.*) \[(.+)\]$'
     let l:output = []
 
+    " modern checkstyle versions
+    let l:pattern = '\v\[(WARN|ERROR)\] [a-zA-Z]?:?[^:]+:(\d+):(\d+)?:? (.*) \[(.+)\]$'
+
     for l:match in ale#util#GetMatches(a:lines, l:pattern)
         call add(l:output, {
         \   'type': l:match[1] is? 'WARN' ? 'W' : 'E',
@@ -15,6 +17,17 @@ function! ale_linters#java#checkstyle#Handle(buffer, lines) abort
         \})
     endfor
 
+    " old checkstyle versions
+    let l:pattern = '\v(.+):(\d+): ([^:]+): (.+)$'
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        call add(l:output, {
+        \   'type': l:match[3] is? 'warning' ? 'W' : 'E',
+        \   'lnum': l:match[2] + 0,
+        \   'text': l:match[4],
+        \})
+    endfor
+
     return l:output
 endfunction
 

test/handler/test_checkstyle_handler.vader

@@ -26,3 +26,16 @@ Execute(The checkstyle handler should parse lines correctly):
   \   '[WARN] whatever:101: ''method def rcurly'' has incorrect indentation level 4, expected level should be 2. [Indentation]',
   \   '[WARN] whatever:63:3: Missing a Javadoc comment. [JavadocMethod]',
   \ ])
+
+Execute(The checkstyle handler should parse lines from older checkstyle versions correctly):
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 289,
+  \     'text': '''method def modifier'' have incorrect indentation level 4, expected level should be 2.',
+  \     'type': 'W',
+  \   },
+  \ ],
+  \ ale_linters#java#checkstyle#Handle(666, [
+  \   '/home/languitar/src/rsb-java/rsb-java/src/main/java/rsb/Listener.java:289: warning: ''method def modifier'' have incorrect indentation level 4, expected level should be 2.',
+  \ ])