Detaching HEAD when checking out the same commit.

Detaching HEAD didn't work in some corner checkout cases.  If, for example,
HEAD is symbolic ref to refs/heads/master, refs/heads/master is ref to commit
c0ffee... then:

    checkout c0ffee...

would leave the HEAD unchanged.

The same symptom occurs when checking out a remote tracking branch or a tag
that references the same commit as refs/heads/master.

In the above case, the RefUpdate class didn't have enough information to decide
if the update needed to detach symbolic ref because it dealt only with new/old
objectIDs. Therefore, this fix introduced the RefUpdate.detachingSymbolicRef
flag.

Bug: 315166
Change-Id: I085c98b77ea8f9104a213978ea0d4ac6fd58f49b
Signed-off-by: Sasa Zivkov <sasa.zivkov@sap.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CheckoutCommandTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CheckoutCommandTest.java
index 21fbe0a134..6e9f851793 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CheckoutCommandTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CheckoutCommandTest.java
@@ -47,6 +47,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -239,4 +240,20 @@ public class CheckoutCommandTest extends RepositoryTestCase {
 			fail(e.getMessage());
 		}
 	}
+
+	@Test
+	public void testDetachedHeadOnCheckout() throws JGitInternalException,
+			RefAlreadyExistsException, RefNotFoundException,
+			InvalidRefNameException, IOException {
+		CheckoutCommand co = git.checkout();
+		co.setName("master").call();
+
+		String commitId = db.getRef(Constants.MASTER).getObjectId().name();
+		co = git.checkout();
+		co.setName(commitId).call();
+
+		Ref head = db.getRef(Constants.HEAD);
+		assertFalse(head.isSymbolic());
+		assertSame(head, head.getTarget());
+	}
 }