Checkout: fix handling if name does not refer to a local branch

The CheckoutCommand does not handle names other than local branch
names properly; it must detach HEAD if such a name is encountered (for
example a commit ID or a remote tracking branch).

Change-Id: I5d55177f4029bcc34fc2649fd564b125a2929cc4
Signed-off-by: Mathias Kinzler <mathias.kinzler@sap.com>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

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

@@ -52,6 +52,7 @@
 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.Ref;
 import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.RepositoryTestCase;
 import org.eclipse.jgit.revwalk.RevCommit;
@@ -97,9 +98,12 @@ public void testCheckout() {
 			git.checkout().setName("test").call();
 			assertEquals("[Test.txt, mode:100644, content:Some change]",
 					indexState(CONTENT));
-			git.checkout().setName("master").call();
+			Ref result = git.checkout().setName("master").call();
 			assertEquals("[Test.txt, mode:100644, content:Hello world]",
 					indexState(CONTENT));
+			assertEquals("refs/heads/master", result.getName());
+			assertEquals("refs/heads/master", git.getRepository()
+					.getFullBranch());
 		} catch (Exception e) {
 			fail(e.getMessage());
 		}
@@ -171,4 +175,17 @@ public void testCheckoutWithNonDeletedFiles() throws Exception {
 			fis.close();
 		}
 	}
+
+	public void testCheckoutCommit() {
+		try {
+			Ref result = git.checkout().setName(initialCommit.name()).call();
+			assertEquals("[Test.txt, mode:100644, content:Hello world]",
+					indexState(CONTENT));
+			assertNull(result);
+			assertEquals(initialCommit.name(), git.getRepository()
+					.getFullBranch());
+		} catch (Exception e) {
+			fail(e.getMessage());
+		}
+	}
 }

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

@@ -128,7 +128,7 @@ public Ref call() throws JGitInternalException, RefAlreadyExistsException,
 			String refLogMessage = "checkout: moving from "
 					+ headRef.getTarget().getName();
 			ObjectId branch = repo.resolve(name);
-			Ref ref = repo.getRef(name);
+
 			if (branch == null)
 				throw new RefNotFoundException(MessageFormat.format(JGitText
 						.get().refNotResolved, name));
@@ -148,11 +148,20 @@ public Ref call() throws JGitInternalException, RefAlreadyExistsException,
 				status = new CheckoutResult(Status.CONFLICTS, fileList);
 				throw e;
 			}
-			RefUpdate refUpdate = repo.updateRef(Constants.HEAD);
+			Ref ref = repo.getRef(name);
+			if (ref != null && !ref.getName().startsWith(Constants.R_HEADS))
+				ref = null;
+			RefUpdate refUpdate = repo.updateRef(Constants.HEAD, ref == null);
 			refUpdate.setForceUpdate(force);
 			refUpdate.setRefLogMessage(refLogMessage + "to "
 					+ newCommit.getName(), false);
-			Result updateResult = refUpdate.link(ref.getName());
+			Result updateResult;
+			if (ref != null)
+				updateResult = refUpdate.link(ref.getName());
+			else {
+				refUpdate.setNewObjectId(newCommit);
+				updateResult = refUpdate.forceUpdate();
+			}
 
 			setCallable(false);
 
@@ -174,8 +183,6 @@ public Ref call() throws JGitInternalException, RefAlreadyExistsException,
 				throw new JGitInternalException(MessageFormat.format(JGitText
 						.get().checkoutUnexpectedResult, updateResult.name()));
 
-			Ref result = repo.getRef(name);
-
 			if (!repo.isBare() && !dco.getToBeDeleted().isEmpty()) {
 				List<File> fileList = new ArrayList<File>();
 				for (String filePath : dco.getToBeDeleted()) {
@@ -185,7 +192,7 @@ public Ref call() throws JGitInternalException, RefAlreadyExistsException,
 			}
 			else
 				status = CheckoutResult.OK_RESULT;
-			return result;
+			return ref;
 		} catch (IOException ioe) {
 			throw new JGitInternalException(ioe.getMessage(), ioe);
 		} finally {