Make GC more robust against corrupt reflogs

With JGit it is possible to write reflog entries where new objectid and
old objectid is null. Such reflogs cause FileRepository GC to crash
because it doesn't expect the new objectid to be null. One case where
this happened is in Gerrit's allProjects repo. In the same way as we
expect the old objectid to be potentially null we should also ignore
null values in the new objectid column.

Change-Id: Icf666c7ef803179b84306ca8deb602369b8df16e

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/GCTest.java

@@ -49,8 +49,8 @@ import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
 import java.io.File;
-import java.util.Collection;
 import java.io.IOException;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
 import java.util.Iterator;
@@ -62,6 +62,7 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 
+import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.file.FileRepository;
 import org.eclipse.jgit.internal.storage.file.GC;
@@ -76,9 +77,9 @@ import org.eclipse.jgit.junit.LocalDiskRepositoryTestCase;
 import org.eclipse.jgit.junit.RepositoryTestCase;
 import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.junit.TestRepository.BranchBuilder;
-import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.junit.TestRepository.CommitBuilder;
 import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.EmptyProgressMonitor;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref.Storage;
@@ -436,6 +437,20 @@ public class GCTest extends LocalDiskRepositoryTestCase {
 		assertEquals(1, stats.numberOfPackFiles);
 	}
 
+	@Test
+	public void testPackRepoWithCorruptReflog() throws Exception {
+		// create a reflog entry "0000... 0000... foobar" by doing an initial
+		// refupdate for HEAD which points to a non-existing ref. The
+		// All-Projects repo of gerrit instances had such entries
+		RefUpdate ru = repo.updateRef(Constants.HEAD);
+		ru.link("refs/to/garbage");
+		tr.branch("refs/heads/master").commit().add("A", "A").add("B", "B")
+				.create();
+		// make sure HEAD exists
+		Git.wrap(repo).checkout().setName("refs/heads/master").call();
+		gc.gc();
+	}
+
 	@Test
 	public void testKeepFiles() throws Exception {
 		BranchBuilder bb = tr.branch("refs/heads/master");
@@ -477,9 +492,10 @@ public class GCTest extends LocalDiskRepositoryTestCase {
 		assertEquals(4, ind2.getObjectCount());
 		for (MutableEntry e: ind1)
 			if (ind2.hasObject(e.toObjectId()))
-			assertFalse(
-					"the following object is in both packfiles: "
-							+ e.toObjectId(), ind2.hasObject(e.toObjectId()));
+				assertFalse(
+						"the following object is in both packfiles: "
+								+ e.toObjectId(),
+						ind2.hasObject(e.toObjectId()));
 	}
 
 	@Test

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java

@@ -555,7 +555,9 @@ public class GC {
 		for (ReflogEntry e : rlEntries) {
 			if (e.getWho().getWhen().getTime() < minTime)
 				break;
-			ret.add(e.getNewId());
+			ObjectId newId = e.getNewId();
+			if (newId != null && !ObjectId.zeroId().equals(newId))
+				ret.add(newId);
 			ObjectId oldId = e.getOldId();
 			if (oldId != null && !ObjectId.zeroId().equals(oldId))
 				ret.add(oldId);