Check for FF_ONLY merges correctly

Bug: 398192
Change-Id: I1253c0ea0632185bbf9f77e32f13ba5842a6e18e

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

@@ -52,6 +52,7 @@ import static org.junit.Assert.fail;
 import java.io.File;
 import java.util.Iterator;
 
+import org.eclipse.jgit.api.MergeCommand.FastForwardMode;
 import org.eclipse.jgit.api.MergeResult.MergeStatus;
 import org.eclipse.jgit.api.errors.InvalidMergeHeadsException;
 import org.eclipse.jgit.lib.Constants;
@@ -203,6 +204,28 @@ public class MergeCommandTest extends RepositoryTestCase {
 		}
 	}
 
+	@Test
+	public void testMergeCannotDoRequiredFastForward() throws Exception {
+		Git git = new Git(db);
+
+		RevCommit first = git.commit().setMessage("first").call();
+		createBranch(first, "refs/heads/side");
+
+		writeTrashFile("a", "a");
+		git.add().addFilepattern("a").call();
+		git.commit().setMessage("second").call();
+
+		checkoutBranch("refs/heads/side");
+		writeTrashFile("b", "b");
+		git.add().addFilepattern("b").call();
+		git.commit().setMessage("third").call();
+
+		MergeResult result = git.merge().include(db.getRef(Constants.MASTER))
+				.setFastForward(FastForwardMode.NO_FF)
+				.call();
+		assertEquals(MergeStatus.ABORTED, result.getMergeStatus());
+	}
+
 	@Theory
 	public void testMergeSuccessAllStrategies(MergeStrategy mergeStrategy)
 			throws Exception {
@@ -1328,6 +1351,22 @@ public class MergeCommandTest extends RepositoryTestCase {
 		assertEquals(StatusCommandTest.set("file2"), stat.getConflicting());
 	}
 
+	@Test
+	public void testFastForwardOnly() throws Exception {
+		Git git = new Git(db);
+		RevCommit initialCommit = git.commit().setMessage("initial commit")
+				.call();
+		createBranch(initialCommit, "refs/heads/branch1");
+		git.commit().setMessage("second commit").call();
+		checkoutBranch("refs/heads/branch1");
+
+		MergeCommand merge = git.merge();
+		merge.setFastForward(FastForwardMode.FF_ONLY);
+		merge.include(db.getRef(Constants.MASTER));
+		MergeResult result = merge.call();
+
+		assertEquals(MergeStatus.FAST_FORWARD, result.getMergeStatus());
+	}
 	private static void setExecutable(Git git, String path, boolean executable) {
 		FS.DETECTED.setExecute(
 				new File(git.getRepository().getWorkTree(), path), executable);

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

@@ -269,7 +269,7 @@ public class MergeCommand extends GitCommand<MergeResult> {
 						headCommit, srcCommit },
 						MergeStatus.ALREADY_UP_TO_DATE, mergeStrategy, null, null);
 			} else if (revWalk.isMergedInto(headCommit, srcCommit)
-					&& fastForwardMode == FastForwardMode.FF) {
+					&& fastForwardMode != FastForwardMode.NO_FF) {
 				// FAST_FORWARD detected: skip doing a real merge but only
 				// update HEAD
 				refLogMessage.append(": " + MergeStatus.FAST_FORWARD); //$NON-NLS-1$
@@ -300,7 +300,7 @@ public class MergeCommand extends GitCommand<MergeResult> {
 						headCommit, srcCommit }, mergeStatus, mergeStrategy,
 						null, msg);
 			} else {
-				if (fastForwardMode == FastForwardMode.FF_ONLY) {
+				if (fastForwardMode == FastForwardMode.NO_FF) {
 					return new MergeResult(headCommit, srcCommit,
 							new ObjectId[] { headCommit, srcCommit },
 							MergeStatus.ABORTED, mergeStrategy, null, null);