Checkstyle command-line no longer reports a usage error if the user specifies a directory with the -r option that does not contain any files. Thanks to Florian for patch #2151706.

src/checkstyle/com/puppycrawl/tools/checkstyle/Main.java

@@ -166,7 +166,7 @@ public final class Main
             files.add(new File(element));
         }
 
-        if (files.isEmpty()) {
+        if (files.isEmpty() && !aLine.hasOption("r")) {
             System.out.println("Must specify files to process");
             usage();
         }

src/xdocs/releasenotes.xml

@@ -32,6 +32,12 @@
           The NCSS complexity checker reported an incorrect fileMax value
           (bug #2161419).
         </li>
+
+        <li>
+          Checkstyle command-line no longer reports a usage error if the
+          user specifies a directory with the <i>-r</i> option that does
+          not contain any files. Thanks to Florian for patch #2151706.
+        </li>
       </ul>
 
       <p>Notes:</p>