DirCacheIterator: Fix reset() and back()

reset() was broken and probably only worked when the position was
at the beginning. More serious was that back() sometimes descended
into the tree rather than skipping backward at the same level. Sometimes
this would result in false conflicts, but one could suspect silent
errors too. back() is called by the NamingConflictTreeWalk when looking
for directory/file conflicts.

Also added toString to DirCacheTree to simplify debugging.

Bug: 396127
Change-Id: Iaa1b4e20e623d84c2e5ac26748f42e991080dbcd

org.eclipse.jgit.test/tst/org/eclipse/jgit/dircache/DirCacheIteratorTest.java

 import org.eclipse.jgit.junit.JGitTestUtil;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.RepositoryTestCase;
+import org.eclipse.jgit.treewalk.AbstractTreeIterator;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.eclipse.jgit.treewalk.filter.PathFilterGroup;
 import org.eclipse.jgit.util.FS;
 		assertEquals(paths.length, pathIdx);
 	}
 
+	@Test
+	public void testReset() throws Exception {
+		final DirCache dc = DirCache.newInCore();
+
+		final FileMode mode = FileMode.REGULAR_FILE;
+		final String[] paths = { "a.", "a/b", "a/c/e", "a/c/f", "a/d", "a0b" };
+		final DirCacheEntry[] ents = new DirCacheEntry[paths.length];
+		for (int i = 0; i < paths.length; i++) {
+			ents[i] = new DirCacheEntry(paths[i]);
+			ents[i].setFileMode(mode);
+		}
+
+		final DirCacheBuilder b = dc.builder();
+		for (int i = 0; i < ents.length; i++)
+			b.add(ents[i]);
+		b.finish();
+
+		DirCacheIterator dci = new DirCacheIterator(dc);
+		assertFalse(dci.eof());
+		assertEquals("a.", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a0b", dci.getEntryPathString());
+		dci.next(1);
+		assertTrue(dci.eof());
+
+		// same entries the second time
+		dci.reset();
+		assertFalse(dci.eof());
+		assertEquals("a.", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a0b", dci.getEntryPathString());
+		dci.next(1);
+		assertTrue(dci.eof());
+
+		// Step backwards
+		dci.back(1);
+		assertFalse(dci.eof());
+		assertEquals("a0b", dci.getEntryPathString());
+		dci.back(1);
+		assertFalse(dci.eof());
+		assertEquals("a", dci.getEntryPathString());
+		dci.back(1);
+		assertFalse(dci.eof());
+		assertEquals("a.", dci.getEntryPathString());
+		assertTrue(dci.first());
+
+		// forward
+		assertFalse(dci.eof());
+		assertEquals("a.", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a0b", dci.getEntryPathString());
+		dci.next(1);
+		assertTrue(dci.eof());
+
+		// backwqrd halways, and forward again
+		dci.back(1);
+		assertFalse(dci.eof());
+		assertEquals("a0b", dci.getEntryPathString());
+		dci.back(1);
+		assertFalse(dci.eof());
+		assertEquals("a", dci.getEntryPathString());
+
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("a0b", dci.getEntryPathString());
+		dci.next(1);
+		assertTrue(dci.eof());
+
+		dci.reset(); // a.
+		dci.next(1); // a
+		AbstractTreeIterator sti = dci.createSubtreeIterator(null);
+		assertEquals("a/b", sti.getEntryPathString());
+		sti.next(1);
+		assertEquals("a/c", sti.getEntryPathString());
+		sti.next(1);
+		assertEquals("a/d", sti.getEntryPathString());
+		sti.back(2);
+		assertEquals("a/b", sti.getEntryPathString());
+
+	}
+
+	@Test
+	public void testBackBug396127() throws Exception {
+		final DirCache dc = DirCache.newInCore();
+
+		final FileMode mode = FileMode.REGULAR_FILE;
+		final String[] paths = { "git-gui/po/fr.po",
+				"git_remote_helpers/git/repo.py" };
+		final DirCacheEntry[] ents = new DirCacheEntry[paths.length];
+		for (int i = 0; i < paths.length; i++) {
+			ents[i] = new DirCacheEntry(paths[i]);
+			ents[i].setFileMode(mode);
+		}
+
+		final DirCacheBuilder b = dc.builder();
+		for (int i = 0; i < ents.length; i++)
+			b.add(ents[i]);
+		b.finish();
+
+		DirCacheIterator dci = new DirCacheIterator(dc);
+		assertFalse(dci.eof());
+		assertEquals("git-gui", dci.getEntryPathString());
+		dci.next(1);
+		assertFalse(dci.eof());
+		assertEquals("git_remote_helpers", dci.getEntryPathString());
+		dci.back(1);
+		assertFalse(dci.eof());
+		assertEquals("git-gui", dci.getEntryPathString());
+		dci.next(1);
+		assertEquals("git_remote_helpers", dci.getEntryPathString());
+		dci.next(1);
+		assertTrue(dci.eof());
+
+	}
+
 	@Test
 	public void testTwoLevelSubtree_FilterPath() throws Exception {
 		final DirCache dc = DirCache.newInCore();

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheIterator.java

 	public void reset() {
 		if (!first()) {
 			ptr = treeStart;
+			nextSubtreePos = 0;
+			currentEntry = null;
+			currentSubtree = null;
 			if (!eof())
 				parseEntry();
 		}
 			if (currentSubtree != null)
 				nextSubtreePos--;
 			ptr--;
-			parseEntry();
+			parseEntry(false);
 			if (currentSubtree != null)
 				ptr -= currentSubtree.getEntrySpan() - 1;
 		}
 	}
 
 	private void parseEntry() {
+		parseEntry(true);
+	}
+
+	private void parseEntry(boolean forward) {
 		currentEntry = cache.getEntry(ptr);
 		final byte[] cep = currentEntry.path;
 
+		if (!forward) {
+			if (nextSubtreePos > 0) {
+				final DirCacheTree p = tree.getChild(nextSubtreePos - 1);
+				if (p.contains(cep, pathOffset, cep.length)) {
+					nextSubtreePos--;
+					currentSubtree = p;
+				}
+			}
+		}
 		if (nextSubtreePos != tree.getChildCount()) {
 			final DirCacheTree s = tree.getChild(nextSubtreePos);
 			if (s.contains(cep, pathOffset, cep.length)) {

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheTree.java

 				return aPos;
 		return -1;
 	}
+
+	@Override
+	public String toString() {
+		return getNameString();
+	}
 }