Fix idOffset when the working tree iterator matches a dircache entry

idOffset is not zero when idBuffer comes from blob in the dircache

Change-Id: Iff768422cba140a5d6a776e2c627b852f079c1da

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

@@ -197,6 +197,31 @@ public class FileTreeIteratorTest extends RepositoryTestCase {
 		assertEquals(expect, top.getEntryObjectId());
 	}
 
+	@Test
+	public void testDirCacheMatchingId() throws Exception {
+		File f = writeTrashFile("file", "content");
+		Git git = new Git(db);
+		writeTrashFile("file", "content");
+		fsTick(f);
+		git.add().addFilepattern("file").call();
+		DirCacheEntry dce = db.readDirCache().getEntry("file");
+		TreeWalk tw = new TreeWalk(db);
+		FileTreeIterator fti = new FileTreeIterator(trash, db.getFS(), db
+				.getConfig().get(WorkingTreeOptions.KEY));
+		tw.addTree(fti);
+		DirCacheIterator dci = new DirCacheIterator(db.readDirCache());
+		tw.addTree(dci);
+		fti.setDirCacheIterator(tw, 1);
+		while (tw.next() && !tw.getPathString().equals("file")) {
+			//
+		}
+		assertEquals(MetadataDiff.EQUAL, fti.compareMetadata(dce));
+		ObjectId fromRaw = ObjectId.fromRaw(fti.idBuffer(), fti.idOffset());
+		assertEquals("6b584e8ece562ebffc15d38808cd6b98fc3d97ea",
+				fromRaw.getName());
+		assertFalse(fti.isModified(dce, false));
+	}
+
 	@Test
 	public void testIsModifiedSymlink() throws Exception {
 		File f = writeTrashFile("symlink", "content");

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

@@ -131,6 +131,9 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 	/** Cached canonical length, initialized from {@link #idBuffer()} */
 	private long canonLen = -1;
 
+	/** The offset of the content id in {@link #idBuffer()} */
+	private int contentIdOffset;
+
 	/**
 	 * Create a new iterator with no parent.
 	 *
@@ -234,11 +237,14 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 					DirCacheIterator.class);
 			if (i != null) {
 				DirCacheEntry ent = i.getDirCacheEntry();
-				if (ent != null && compareMetadata(ent) == MetadataDiff.EQUAL)
+				if (ent != null && compareMetadata(ent) == MetadataDiff.EQUAL) {
-					return i.idBuffer();
+					contentIdOffset = i.idOffset();
+					contentIdFromPtr = ptr;
+					return contentId = i.idBuffer();
+				}
+				contentIdOffset = 0;
 			}
 		}
-
 		switch (mode & FileMode.TYPE_MASK) {
 		case FileMode.TYPE_FILE:
 			contentIdFromPtr = ptr;
@@ -427,7 +433,7 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 
 	@Override
 	public int idOffset() {
-		return 0;
+		return contentIdOffset;
 	}
 
 	@Override