Do not cherry-pick merge commits during rebase

Rebase computes the list of commits that are included in
the merges, just like Git does, so do not try to include
the merge commits. Re-recreating merges during rebase is
a bit more complicated and might be a useful future extension,
but for now just linearize during rebase.

Change-Id: I61239d265f395e5ead580df2528e46393dc6bdbd
Signed-off-by: Robin Stocker <robin@nibor.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/RebaseCommandTest.java

@@ -42,6 +42,9 @@
  */
 package org.eclipse.jgit.api;
 
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.not;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -62,7 +65,6 @@ import org.eclipse.jgit.api.RebaseCommand.InteractiveHandler;
 import org.eclipse.jgit.api.RebaseCommand.Operation;
 import org.eclipse.jgit.api.RebaseCommand.Step;
 import org.eclipse.jgit.api.RebaseResult.Status;
-import org.eclipse.jgit.api.errors.JGitInternalException;
 import org.eclipse.jgit.api.errors.RefNotFoundException;
 import org.eclipse.jgit.api.errors.UnmergedPathsException;
 import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
@@ -161,72 +163,89 @@ public class RebaseCommandTest extends RepositoryTestCase {
 		assertEquals(Status.FAST_FORWARD, res.getStatus());
 	}
 
+	/**
+	 * Create the following commits and then attempt to rebase topic onto
+	 * master. This will serialize the branches.
+	 *
+	 * <pre>
+	 * A - B (master)
+	 *   \
+	 *    C - D - F (topic)
+	 *     \      /
+	 *      E  -  (side)
+	 * </pre>
+	 *
+	 * into
+	 *
+	 * <pre>
+	 * A - B - (master)  C' - D' - E' (topic')
+	 *   \
+	 *    C - D - F (topic)
+	 *     \      /
+	 *      E  -  (side)
+	 * </pre>
+	 *
+	 * @throws Exception
+	 */
 	@Test
-	public void testRebaseFailsCantCherryPickMergeCommits()
+	public void testRebaseShouldIgnoreMergeCommits()
 			throws Exception {
-		/**
-		 * Create the following commits and then attempt to rebase topic onto
-		 * master. This will fail as the cherry-pick list C, D, E an F contains
-		 * a merge commit (F).
-		 *
-		 * <pre>
-		 * A - B (master)
-		 *   \
-		 *    C - D - F (topic)
-		 *     \      /
-		 *      E  -  (side)
-		 * </pre>
-		 */
 		// create file1 on master
 		writeTrashFile(FILE1, FILE1);
 		git.add().addFilepattern(FILE1).call();
-		RevCommit first = git.commit().setMessage("Add file1").call();
+		RevCommit a = git.commit().setMessage("Add file1").call();
 		assertTrue(new File(db.getWorkTree(), FILE1).exists());
 
 		// create a topic branch
-		createBranch(first, "refs/heads/topic");
+		createBranch(a, "refs/heads/topic");
 
 		// update FILE1 on master
 		writeTrashFile(FILE1, "blah");
 		git.add().addFilepattern(FILE1).call();
-		git.commit().setMessage("updated file1 on master").call();
+		RevCommit b = git.commit().setMessage("updated file1 on master").call();
 
 		checkoutBranch("refs/heads/topic");
 		writeTrashFile("file3", "more changess");
 		git.add().addFilepattern("file3").call();
-		RevCommit topicCommit = git.commit()
+		RevCommit c = git.commit()
 				.setMessage("update file3 on topic").call();
 
 		// create a branch from the topic commit
-		createBranch(topicCommit, "refs/heads/side");
+		createBranch(c, "refs/heads/side");
 
 		// second commit on topic
 		writeTrashFile("file2", "file2");
 		git.add().addFilepattern("file2").call();
-		git.commit().setMessage("Add file2").call();
+		RevCommit d = git.commit().setMessage("Add file2").call();
 		assertTrue(new File(db.getWorkTree(), "file2").exists());
 
 		// switch to side branch and update file2
 		checkoutBranch("refs/heads/side");
 		writeTrashFile("file3", "more change");
 		git.add().addFilepattern("file3").call();
-		RevCommit sideCommit = git.commit().setMessage("update file2 on side")
+		RevCommit e = git.commit().setMessage("update file2 on side")
 				.call();
 
-		// switch back to topic and merge in side
+		// switch back to topic and merge in side, creating f
 		checkoutBranch("refs/heads/topic");
-		MergeResult result = git.merge().include(sideCommit.getId())
+		MergeResult result = git.merge().include(e.getId())
 				.setStrategy(MergeStrategy.RESOLVE).call();
 		assertEquals(MergeStatus.MERGED, result.getMergeStatus());
+		RebaseResult res = git.rebase().setUpstream("refs/heads/master").call();
+		assertEquals(Status.OK, res.getStatus());
 
-		try {
-			RebaseResult rebase = git.rebase().setUpstream("refs/heads/master")
-					.call();
-			fail("MultipleParentsNotAllowedException expected: "
-					+ rebase.getStatus());
-		} catch (JGitInternalException e) {
-			// expected
-		}
+		RevWalk rw = new RevWalk(db);
+		rw.markStart(rw.parseCommit(db.resolve("refs/heads/topic")));
+		assertDerivedFrom(rw.next(), e);
+		assertDerivedFrom(rw.next(), d);
+		assertDerivedFrom(rw.next(), c);
+		assertEquals(b, rw.next());
+		assertEquals(a, rw.next());
+	}
+
+	static void assertDerivedFrom(RevCommit derived, RevCommit original) {
+		assertThat(derived, not(equalTo(original)));
+		assertEquals(original.getFullMessage(), derived.getFullMessage());
 	}
 
 	@Test

org.eclipse.jgit/src/org/eclipse/jgit/api/RebaseCommand.java

@@ -640,11 +640,7 @@ public class RebaseCommand extends GitCommand<RebaseResult> {
 		List<RevCommit> cherryPickList = new ArrayList<RevCommit>();
 		for (RevCommit commit : commitsToUse) {
 			if (commit.getParentCount() != 1)
-				throw new JGitInternalException(
-						MessageFormat.format(
-								JGitText.get().canOnlyCherryPickCommitsWithOneParent,
-								commit.name(),
-								Integer.valueOf(commit.getParentCount())));
+				continue;
 			cherryPickList.add(commit);
 		}