Ensure resetting on commit id

When reset command was called with tag name as parameter the resulting
HEAD was set to the tag's SHA-1 which is a bug. This patch ensures that
repository.resolve() call always returns commit id.

Change-Id: I219b898c620a75c497c8652dbf4735fd094c4d7c
Signed-off-by: Dariusz Luksza <dariusz@luksza.org>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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

@@ -42,6 +42,7 @@
  */
 package org.eclipse.jgit.api;
 
+import static org.eclipse.jgit.api.ResetCommand.ResetType.HARD;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -305,6 +306,25 @@ public class ResetCommandTest extends RepositoryTestCase {
 		assertFalse(inIndex(untrackedFile.getName()));
 	}
 
+	@Test
+	public void testHardResetOnTag() throws Exception {
+		setupRepository();
+		String tagName = "initialtag";
+		git.tag().setName(tagName).setObjectId(secondCommit)
+				.setMessage("message").call();
+
+		DirCacheEntry preReset = DirCache.read(db.getIndexFile(), db.getFS())
+				.getEntry(indexFile.getName());
+		assertNotNull(preReset);
+
+		git.add().addFilepattern(untrackedFile.getName()).call();
+
+		git.reset().setRef(tagName).setMode(HARD).call();
+
+		ObjectId head = db.resolve(Constants.HEAD);
+		assertTrue(head.equals(secondCommit));
+	}
+
 	private void assertReflog(ObjectId prevHead, ObjectId head)
 			throws IOException {
 		// Check the reflog for HEAD

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

@@ -150,7 +150,7 @@ public class ResetCommand extends GitCommand<Ref> {
 			// resolve the ref to a commit
 			final ObjectId commitId;
 			try {
-				commitId = repo.resolve(ref);
+				commitId = repo.resolve(ref + "^{commit}");
 				if (commitId == null) {
 					// @TODO throw an InvalidRefNameException. We can't do that
 					// now because this would break the API