Add "Conflicts" section to merge message on conflict

The same as with cherry-pick, the commit message of a merge should
include a "Conflicts" section when the merge resulted in conflicts.

Change-Id: I6261dc898262322924af5ca1bef841a654b0df55
Signed-off-by: Robin Stocker <robin@nibor.org>

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

@@ -54,6 +54,7 @@ import java.util.Iterator;
 import org.eclipse.jgit.api.MergeResult.MergeStatus;
 import org.eclipse.jgit.api.errors.InvalidMergeHeadsException;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.RepositoryState;
 import org.eclipse.jgit.lib.RepositoryTestCase;
 import org.eclipse.jgit.merge.MergeStrategy;
@@ -204,6 +205,37 @@ public class MergeCommandTest extends RepositoryTestCase {
 		assertEquals(RepositoryState.MERGING, db.getRepositoryState());
 	}
 
+	@Test
+	public void testMergeMessage() throws Exception {
+		Git git = new Git(db);
+
+		writeTrashFile("a", "1\na\n3\n");
+		git.add().addFilepattern("a").call();
+		RevCommit initialCommit = git.commit().setMessage("initial").call();
+
+		createBranch(initialCommit, "refs/heads/side");
+		checkoutBranch("refs/heads/side");
+
+		writeTrashFile("a", "1\na(side)\n3\n");
+		git.add().addFilepattern("a").call();
+		git.commit().setMessage("side").call();
+
+		checkoutBranch("refs/heads/master");
+
+		writeTrashFile("a", "1\na(main)\n3\n");
+		git.add().addFilepattern("a").call();
+		git.commit().setMessage("main").call();
+
+		Ref sideBranch = db.getRef("side");
+
+		git.merge().include(sideBranch)
+				.setStrategy(MergeStrategy.RESOLVE).call();
+
+		assertEquals("Merge branch 'side'\n\nConflicts:\n\ta\n",
+				db.readMergeCommitMsg());
+
+	}
+
 	@Test
 	public void testMergeNonVersionedPaths() throws Exception {
 		Git git = new Git(db);

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

@@ -189,14 +189,16 @@ public class MergeCommand extends GitCommand<MergeResult> {
 						mergeStrategy, null, null);
 			} else {
 
-				repo.writeMergeCommitMsg(new MergeMessageFormatter().format(
-						commits, head));
+				String mergeMessage = new MergeMessageFormatter().format(
+						commits, head);
+				repo.writeMergeCommitMsg(mergeMessage);
 				repo.writeMergeHeads(Arrays.asList(ref.getObjectId()));
 				ThreeWayMerger merger = (ThreeWayMerger) mergeStrategy
 						.newMerger(repo);
 				boolean noProblems;
 				Map<String, org.eclipse.jgit.merge.MergeResult<?>> lowLevelResults = null;
 				Map<String, MergeFailureReason> failingPaths = null;
+				List<String> unmergedPaths = null;
 				if (merger instanceof ResolveMerger) {
 					ResolveMerger resolveMerger = (ResolveMerger) merger;
 					resolveMerger.setCommitNames(new String[] {
@@ -206,6 +208,7 @@ public class MergeCommand extends GitCommand<MergeResult> {
 					lowLevelResults = resolveMerger
 							.getMergeResults();
 					failingPaths = resolveMerger.getFailingPaths();
+					unmergedPaths = resolveMerger.getUnmergedPaths();
 				} else
 					noProblems = merger.merge(headCommit, srcCommit);
 
@@ -230,13 +233,18 @@ public class MergeCommand extends GitCommand<MergeResult> {
 										headCommit.getId(), srcCommit.getId() },
 								MergeStatus.FAILED, mergeStrategy,
 								lowLevelResults, failingPaths, null);
-					} else
+					} else {
+						String mergeMessageWithConflicts = new MergeMessageFormatter()
+								.formatWithConflicts(mergeMessage,
+										unmergedPaths);
+						repo.writeMergeCommitMsg(mergeMessageWithConflicts);
 						return new MergeResult(null,
 								merger.getBaseCommit(0, 1),
 								new ObjectId[] { headCommit.getId(),
 										srcCommit.getId() },
 								MergeStatus.CONFLICTING, mergeStrategy,
 								lowLevelResults, null);
+					}
 				}
 			}
 		} catch (IOException e) {