Fix for Iff768422c, use offset 0 when going back to work tree iterator

In Iff768422c the offset used for the content id was fixed to use  the
offset that applied to the dircache iterator. Unfortunately the index
for the dircache content id offset stuck for entries that were not in
the index. Few caller probably cared about that, unless it actually
caused an ArrayIndexOutOfBoundsException.

Change-Id: Ic9f0e77c8ea3a0770d88565e94392e76853e3006

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

@@ -49,6 +49,7 @@ import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 import java.io.File;
+import java.io.IOException;
 import java.security.MessageDigest;
 
 import org.eclipse.jgit.api.Git;
@@ -58,6 +59,9 @@ import org.eclipse.jgit.dircache.DirCacheEditor;
 import org.eclipse.jgit.dircache.DirCacheEntry;
 import org.eclipse.jgit.dircache.DirCacheIterator;
 import org.eclipse.jgit.dircache.DirCacheEditor.PathEdit;
+import org.eclipse.jgit.errors.CorruptObjectException;
+import org.eclipse.jgit.errors.IncorrectObjectTypeException;
+import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
@@ -429,6 +433,43 @@ public class FileTreeIteratorTest extends RepositoryTestCase {
 		assertTrue(indexIter.idEqual(workTreeIter));
 	}
 
+	@Test
+	public void idOffset() throws Exception {
+		Git git = new Git(db);
+		writeTrashFile("fileAinfsonly", "A");
+		File fileBinindex = writeTrashFile("fileBinindex", "B");
+		fsTick(fileBinindex);
+		git.add().addFilepattern("fileBinindex").call();
+		writeTrashFile("fileCinfsonly", "C");
+		TreeWalk tw = new TreeWalk(db);
+		DirCacheIterator indexIter = new DirCacheIterator(db.readDirCache());
+		FileTreeIterator workTreeIter = new FileTreeIterator(db);
+		tw.addTree(indexIter);
+		tw.addTree(workTreeIter);
+		workTreeIter.setDirCacheIterator(tw, 0);
+		assertEntry("d46c305e85b630558ee19cc47e73d2e5c8c64cdc", "a,", tw);
+		assertEntry("58ee403f98538ec02409538b3f80adf610accdec", "a,b", tw);
+		assertEntry("0000000000000000000000000000000000000000", "a", tw);
+		assertEntry("b8d30ff397626f0f1d3538d66067edf865e201d6", "a0b", tw);
+		// The reason for adding this test. Check that the id is correct for
+		// mixed
+		assertEntry("8c7e5a667f1b771847fe88c01c3de34413a1b220",
+				"fileAinfsonly", tw);
+		assertEntry("7371f47a6f8bd23a8fa1a8b2a9479cdd76380e54", "fileBinindex",
+				tw);
+		assertEntry("96d80cd6c4e7158dbebd0849f4fb7ce513e5828c",
+				"fileCinfsonly", tw);
+		assertFalse(tw.next());
+	}
+
+	private void assertEntry(String sha1string, String path, TreeWalk tw)
+			throws MissingObjectException, IncorrectObjectTypeException,
+			CorruptObjectException, IOException {
+		assertTrue(tw.next());
+		assertEquals(path, tw.getPathString());
+		assertEquals(sha1string, tw.getObjectId(1).getName() /* 1=filetree here */);
+	}
+
 	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

@@ -243,6 +243,8 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 					return contentId = i.idBuffer();
 				}
 				contentIdOffset = 0;
+			} else {
+				contentIdOffset = 0;
 			}
 		}
 		switch (mode & FileMode.TYPE_MASK) {