Fix exception on conflicts with recursive merge

When there are conflicts with a recursive merge, the conflicting paths
are stored in unmergedPaths (field in ResolveMerger). Later, when the
MergeResult is constructed in MergeCommand, getBaseCommit is called,
which computes the merge base a second time.

In case of RecursiveMerger, getBaseCommit merges the multiple merge
bases into one. It does this not by creating a new ResolveMerger but
instead calling mergeTrees. The problem with mergeTrees is that at the
end, it checks if unmergedPaths is non-empty and returns false in that
case.

Because unmergedPaths was already non-empty because of the real merge,
it thinks that there were conflicts when computing the merge base again,
when there really were none.

This can be fixed by storing the base commit when computing it and then
returning that instead of computing it a second time.

Note that another possible fix would be to just use a new ResolveMerger
for merging the merge bases instead. This would also remove the need to
remember the old value of dircache, inCore and workingTreeIterator (see
RecursiveMerger#getBaseCommit).

Bug: 419641
Change-Id: Ib2ebf4e177498c22a9098aa225e3cfcf16bbd958
Signed-off-by: Robin Stocker <robin@nibor.org>

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

 import org.eclipse.jgit.api.MergeResult.MergeStatus;
 import org.eclipse.jgit.api.errors.InvalidMergeHeadsException;
 import org.eclipse.jgit.junit.RepositoryTestCase;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.junit.TestRepository.BranchBuilder;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.RepositoryState;
 import org.eclipse.jgit.merge.MergeStrategy;
 import org.eclipse.jgit.merge.ResolveMerger.MergeFailureReason;
 
 		assertEquals(MergeStatus.ABORTED, result.getMergeStatus());
 	}
+
+	@Test
+	public void testRecursiveMergeWithConflict() throws Exception {
+		TestRepository<Repository> db_t = new TestRepository<Repository>(db);
+		BranchBuilder master = db_t.branch("master");
+		RevCommit m0 = master.commit().add("f", "1\n2\n3\n4\n5\n6\n7\n8\n9\n")
+				.message("m0").create();
+		RevCommit m1 = master.commit()
+				.add("f", "1-master\n2\n3\n4\n5\n6\n7\n8\n9\n").message("m1")
+				.create();
+		db_t.getRevWalk().parseCommit(m1);
+
+		BranchBuilder side = db_t.branch("side");
+		RevCommit s1 = side.commit().parent(m0)
+				.add("f", "1\n2\n3\n4\n5\n6\n7\n8\n9-side\n").message("s1")
+				.create();
+		RevCommit s2 = side.commit().parent(m1)
+				.add("f", "1-master\n2\n3\n4\n5\n6\n7-res(side)\n8\n9-side\n")
+				.message("s2(merge)").create();
+		master.commit().parent(s1)
+				.add("f", "1-master\n2\n3\n4\n5\n6\n7-conflict\n8\n9-side\n")
+				.message("m2(merge)").create();
+
+		Git git = Git.wrap(db);
+		git.checkout().setName("master").call();
+
+		MergeResult result = git.merge().setStrategy(MergeStrategy.RECURSIVE)
+				.include("side", s2).call();
+		assertEquals(MergeStatus.CONFLICTING, 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

 					if (failingPaths != null) {
 						repo.writeMergeCommitMsg(null);
 						repo.writeMergeHeads(null);
-						return new MergeResult(null,
-								merger.getBaseCommit(0, 1),
+						return new MergeResult(null, merger.getBaseCommitId(),
 								new ObjectId[] {
 										headCommit.getId(), srcCommit.getId() },
 								MergeStatus.FAILED, mergeStrategy,
 								.formatWithConflicts(mergeMessage,
 										unmergedPaths);
 						repo.writeMergeCommitMsg(mergeMessageWithConflicts);
-						return new MergeResult(null,
-								merger.getBaseCommit(0, 1),
+						return new MergeResult(null, merger.getBaseCommitId(),
 								new ObjectId[] { headCommit.getId(),
 										srcCommit.getId() },
 								MergeStatus.CONFLICTING, mergeStrategy,

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

 							.getFailingPaths();
 					if (failingPaths != null)
 						failingResult = new MergeResult(null,
-								merger.getBaseCommit(0, 1),
+								merger.getBaseCommitId(),
 								new ObjectId[] { headCommit.getId(),
 										srcParent.getId() },
 								MergeStatus.FAILED, MergeStrategy.RECURSIVE,
 								merger.getMergeResults(), failingPaths, null);
 					else
 						failingResult = new MergeResult(null,
-								merger.getBaseCommit(0, 1),
+								merger.getBaseCommitId(),
 								new ObjectId[] { headCommit.getId(),
 										srcParent.getId() },
 								MergeStatus.CONFLICTING,

org.eclipse.jgit/src/org/eclipse/jgit/merge/Merger.java

 /*
- * Copyright (C) 2008-2009, Google Inc.
+ * Copyright (C) 2008-2013, Google Inc.
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevObject;
 import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.revwalk.filter.RevFilter;
 import org.eclipse.jgit.treewalk.AbstractTreeIterator;
 import org.eclipse.jgit.treewalk.CanonicalTreeParser;
-import org.eclipse.jgit.treewalk.EmptyTreeIterator;
 
 /**
  * Instance of a specific {@link MergeStrategy} for a single {@link Repository}.
 	}
 
 	/**
-	 * Create an iterator to walk the merge base of two commits.
-	 *
-	 * @param a
-	 *            the first commit in {@link #sourceObjects}.
-	 * @param b
-	 *            the second commit in {@link #sourceObjects}.
-	 * @return the new iterator
-	 * @throws IncorrectObjectTypeException
-	 *             one of the input objects is not a commit.
-	 * @throws IOException
-	 *             objects are missing or multiple merge bases were found.
-	 * @since 3.0
+	 * @return the ID of the commit that was used as merge base for merging, or
+	 *         null if no merge base was used or it was set manually
+	 * @since 3.2
 	 */
-	protected AbstractTreeIterator mergeBase(RevCommit a, RevCommit b)
-			throws IOException {
-		RevCommit base = getBaseCommit(a, b);
-		return (base == null) ? new EmptyTreeIterator() : openTree(base.getTree());
-	}
+	public abstract ObjectId getBaseCommitId();
 
 	/**
 	 * Return the merge base of two commits.
 	 *             one of the input objects is not a commit.
 	 * @throws IOException
 	 *             objects are missing or multiple merge bases were found.
+	 * @deprecated use {@link #getBaseCommitId()} instead, as that does not
+	 *             require walking the commits again
 	 */
+	@Deprecated
 	public RevCommit getBaseCommit(final int aIdx, final int bIdx)
 			throws IncorrectObjectTypeException,
 			IOException {

org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategyOneSided.java

 		public ObjectId getResultTreeId() {
 			return sourceTrees[treeIndex];
 		}
+
+		@Override
+		public ObjectId getBaseCommitId() {
+			return null;
+		}
 	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/merge/ThreeWayMerger.java

 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.treewalk.AbstractTreeIterator;
+import org.eclipse.jgit.treewalk.EmptyTreeIterator;
 
 /** A merge of 2 trees, using a common base ancestor tree. */
 public abstract class ThreeWayMerger extends Merger {
 	private RevTree baseTree;
 
+	private ObjectId baseCommitId;
+
 	/**
 	 * Create a new merge instance for a repository.
 	 *
 		return super.merge(tips);
 	}
 
+	@Override
+	public ObjectId getBaseCommitId() {
+		return baseCommitId;
+	}
+
 	/**
 	 * Create an iterator to walk the merge base.
 	 *
 	protected AbstractTreeIterator mergeBase() throws IOException {
 		if (baseTree != null)
 			return openTree(baseTree);
-		return mergeBase(sourceCommits[0], sourceCommits[1]);
+		RevCommit baseCommit = (baseCommitId != null) ? walk
+				.parseCommit(baseCommitId) : getBaseCommit(sourceCommits[0],
+				sourceCommits[1]);
+		if (baseCommit == null) {
+			baseCommitId = null;
+			return new EmptyTreeIterator();
+		} else {
+			baseCommitId = baseCommit.toObjectId();
+			return openTree(baseCommit.getTree());
+		}
 	}
 }