Fixed creation of branch from a tag

Creation of a branch X from an annotated tag, as the starting point,
resulted into .git/refs/heads/X containing the ID of the annotated tag
instead of the ID of the tagged commit.

This fix peels the tag ref before using it as the starting point for
the newly created branch.

Bug: 340836
Change-Id: I01c7325770ecb37f5bf8ddb2a22f802466524f24
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

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

 import org.eclipse.jgit.api.errors.RefAlreadyExistsException;
 import org.eclipse.jgit.api.errors.RefNotFoundException;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.RepositoryTestCase;
 import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevTag;
 import org.eclipse.jgit.transport.FetchResult;
 import org.eclipse.jgit.transport.RefSpec;
 import org.eclipse.jgit.transport.RemoteConfig;
 		assertEquals(newBranch.getTarget().getObjectId(), initialCommit.getId());
 	}
 
+	@Test
+	public void testCreateFromLightweightTag() throws Exception {
+		RefUpdate rup = db.updateRef("refs/tags/V10");
+		rup.setNewObjectId(initialCommit);
+		rup.setExpectedOldObjectId(ObjectId.zeroId());
+		rup.update();
+
+		Ref branch = git.branchCreate().setName("FromLightweightTag")
+				.setStartPoint("refs/tags/V10").call();
+		assertEquals(initialCommit.getId(), branch.getObjectId());
+
+	}
+
+	@Test
+	public void testCreateFromAnnotatetdTag() throws Exception {
+		RevTag tag = git.tag().setName("V10").setObjectId(secondCommit).call();
+		Ref branch = git.branchCreate().setName("FromAnnotatedTag")
+				.setStartPoint("refs/tags/V10").call();
+		assertFalse(tag.getId().equals(branch.getObjectId()));
+		assertEquals(secondCommit.getId(), branch.getObjectId());
+	}
+
 	@Test
 	public void testDelete() throws Exception {
 		createBranch(git, "ForDelete", false, "master", null);

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

 			RefNotFoundException, InvalidRefNameException {
 		checkCallable();
 		processOptions();
+		RevWalk revWalk = new RevWalk(repo);
 		try {
 			Ref refToCheck = repo.getRef(name);
 			boolean exists = refToCheck != null
 				if (startCommit != null)
 					baseCommit = startCommit.getShortMessage();
 				else {
-					RevCommit commit = new RevWalk(repo).parseCommit(repo
+					RevCommit commit = revWalk.parseCommit(repo
 							.resolve(startPoint));
 					baseCommit = commit.getShortMessage();
 				}
 				else
 					refLogMessage = "branch: Created from branch " + baseBranch;
 			} else {
+				startAt = revWalk.peel(revWalk.parseAny(startAt));
 				if (exists)
 					refLogMessage = "branch: Reset start-point to tag "
 							+ startPointFullName;
 			return result;
 		} catch (IOException ioe) {
 			throw new JGitInternalException(ioe.getMessage(), ioe);
+		} finally {
+			revWalk.release();
 		}
 	}