Do not rely on filemode differences in case of symbolic links

When checking whether a file in the working tree has been modified -
WorkingTreeIterator.isModified() - we should not trust the filemode
in case of symbolic links, but check the timestamp and also the
content, if requested. Without this fix symlinks will always be shown
in EGit as modified files on Windows systems.

Change-Id: I367c807df5a7e85e828ddacff7fee7901441f187
Signed-off-by: Philipp Thun <philipp.thun@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/FileTreeIteratorTest.java

@@ -46,6 +46,9 @@ package org.eclipse.jgit.treewalk;
 import java.io.File;
 import java.security.MessageDigest;
 
+import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.dircache.DirCacheCheckout;
+import org.eclipse.jgit.dircache.DirCacheEntry;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
@@ -175,6 +178,24 @@ public class FileTreeIteratorTest extends RepositoryTestCase {
 		assertEquals(expect, top.getEntryObjectId());
 	}
 
+	public void testIsModifiedSymlink() throws Exception {
+		File f = writeTrashFile("symlink", "content");
+		Git git = new Git(db);
+		git.add().addFilepattern("symlink").call();
+		git.commit().setMessage("commit").call();
+
+		// Modify previously committed DirCacheEntry and write it back to disk
+		DirCacheEntry dce = db.readDirCache().getEntry("symlink");
+		dce.setFileMode(FileMode.SYMLINK);
+		DirCacheCheckout.checkoutEntry(db, f, dce);
+
+		FileTreeIterator fti = new FileTreeIterator(trash, db.getFS(), db
+				.getConfig().get(WorkingTreeOptions.KEY));
+		while (!fti.getEntryPathString().equals("symlink"))
+			fti.next(1);
+		assertFalse(fti.isModified(dce, false));
+	}
+
 	private static String nameOf(final AbstractTreeIterator i) {
 		return RawParseUtils.decode(Constants.CHARSET, i.path, 0, i.pathLen);
 	}

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java

@@ -556,15 +556,19 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 		// bitwise presentation of modeDiff we'll have a '1' when the two modes
 		// differ at this position.
 		int modeDiff = getEntryRawMode() ^ entry.getRawMode();
-		// Ignore the executable file bits if checkFilemode tells me to do so.
-		// Ignoring is done by setting the bits representing a EXECUTABLE_FILE
-		// to '0' in modeDiff
+
+		// Do not rely on filemode differences in case of symbolic links
+		if (modeDiff != 0 && !FileMode.SYMLINK.equals(entry.getRawMode())) {
+			// Ignore the executable file bits if WorkingTreeOptions tell me to
+			// do so. Ignoring is done by setting the bits representing a
+			// EXECUTABLE_FILE to '0' in modeDiff
 			if (!state.options.isFileMode())
 				modeDiff &= ~FileMode.EXECUTABLE_FILE.getBits();
 			if (modeDiff != 0)
 				// Report a modification if the modes still (after potentially
 				// ignoring EXECUTABLE_FILE bits) differ
 				return true;
+		}
 
 		// Git under windows only stores seconds so we round the timestamp
 		// Java gives us if it looks like the timestamp in index is seconds