[JENKINS-13202] 646154f1 refinement: resolveSymlink is documented to return...

[JENKINS-13202] 646154f1 refinement: resolveSymlink is documented to return null, not throw an exception, when called on a regular file.

changelog.html

@@ -61,6 +61,9 @@ Upcoming changes</a>
   <li class=bug>
     Build records were broken if timezone was changed while running.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-15816">issue 15816</a>)
+  <li class=bug>
+    Symlink detection refinement on Java 7.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-13202">issue 13202</a>)
   <li class='major bug'>
     Displaying massive test suite results could bring down Jenkins.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-15818">issue 15818</a>)

core/src/main/java/hudson/Util.java

@@ -1110,6 +1110,13 @@ public class Util {
             if (x2 instanceof UnsupportedOperationException) {
                 return null; // no symlinks on this platform
             }
+            try {
+                if (Class.forName("java.nio.file.NotLinkException").isInstance(x2)) {
+                    return null;
+                }
+            } catch (ClassNotFoundException x3) {
+                assert false : x3; // should be Java 7+ here
+            }
             if (x2 instanceof IOException) {
                 throw (IOException) x2;
             }

core/src/test/java/hudson/UtilTest.java

@@ -171,6 +171,7 @@ public class UtilTest {
         File d = Util.createTempDir();
         try {
             new FilePath(new File(d, "a")).touch(0);
+            assertNull(Util.resolveSymlink(new File(d, "a")));
             Util.createSymlink(d,"a","x", l);
             assertEquals("a",Util.resolveSymlink(new File(d,"x")));