NameRevCommand: Don't use merge cost for first parent

Treat first parent traversals as 1 and higher parents as MERGE_COST,
to match git name-rev. Allow overriding the merge cost during tests to
avoid creating 2^16 commits on the fly.

Change-Id: I0175e0c3ab1abe6722e4241abe2f106d1fe92a69

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

@@ -162,7 +162,7 @@ public class NameRevCommandTest extends RepositoryTestCase {
 	}
 
 	@Test
-	public void oneMergeDifferentLengths() throws Exception {
+	public void onePathMergeLongerFirstParentPath() throws Exception {
 		// 0--1--2--4
 		//  \--3---/
 		RevCommit c0 = tr.commit().create();
@@ -171,27 +171,24 @@ public class NameRevCommandTest extends RepositoryTestCase {
 		RevCommit c3 = tr.commit().parent(c0).create();
 		RevCommit c4 = tr.commit().parent(c2).parent(c3).create();
 		tr.update("master", c4);
-		assertOneResult("master^2~1", c0);
+		assertOneResult("master^2", c3);
+		assertOneResult("master~3", c0);
 	}
 
 	@Test
-	public void longerPathWithoutMerge() throws Exception {
-		// 0--1--2--4         <- master
-		//  \  \-3-/
-		//   \--5--6--7--8--9 <- branch
+	public void multiplePathsSecondParent() throws Exception {
+		// 0--...--2
+		//  \--1--/
 		RevCommit c0 = tr.commit().create();
 		RevCommit c1 = tr.commit().parent(c0).create();
-		RevCommit c2 = tr.commit().parent(c1).create();
-		RevCommit c3 = tr.commit().parent(c1).create();
-		RevCommit c4 = tr.commit().parent(c2).parent(c3).create();
-		RevCommit c5 = tr.commit().parent(c0).create();
-		RevCommit c6 = tr.commit().parent(c5).create();
-		RevCommit c7 = tr.commit().parent(c6).create();
-		RevCommit c8 = tr.commit().parent(c7).create();
-		RevCommit c9 = tr.commit().parent(c8).create();
-		tr.update("master", c4);
-		tr.update("branch", c9);
-		assertOneResult("branch~5", c0);
+		RevCommit c = c0;
+		int mergeCost = 5;
+		for (int i = 0; i < mergeCost; i++) {
+			c = tr.commit().parent(c).create();
+		}
+		RevCommit c2 = tr.commit().parent(c).parent(c1).create();
+		tr.update("master", c2);
+		assertOneResult("master^2~1", git.nameRev().setMergeCost(mergeCost), c0);
 	}
 
 	private static void assertOneResult(String expected, NameRevCommand nameRev,

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

@@ -112,6 +112,7 @@ public class NameRevCommand extends GitCommand<Map<ObjectId, String>> {
 	private final List<String> prefixes;
 	private final List<Ref> refs;
 	private final List<ObjectId> revs;
+	private int mergeCost;
 
 	/**
 	 * Create a new name-rev command.
@@ -120,6 +121,7 @@ public class NameRevCommand extends GitCommand<Map<ObjectId, String>> {
 	 */
 	protected NameRevCommand(Repository repo) {
 		super(repo);
+		mergeCost = MERGE_COST;
 		prefixes = new ArrayList<String>(2);
 		refs = new ArrayList<Ref>();
 		revs = new ArrayList<ObjectId>(2);
@@ -147,9 +149,9 @@ public class NameRevCommand extends GitCommand<Map<ObjectId, String>> {
 					break;
 				if (c.getCommitTime() < cutoff)
 					continue;
-				long cost = c.cost + (c.getParentCount() > 1 ? MERGE_COST : 1);
 				for (int i = 0; i < c.getParentCount(); i++) {
 					NameRevCommit p = (NameRevCommit) walk.parseCommit(c.getParent(i));
+					long cost = c.cost + (i > 0 ? mergeCost : 1);
 					if (p.tip == null || compare(c.tip, cost, p.tip, p.cost) < 0) {
 						if (i > 0) {
 							p.tip = c.format().append('^').append(i + 1).toString();
@@ -298,6 +300,11 @@ public class NameRevCommand extends GitCommand<Map<ObjectId, String>> {
 		return this;
 	}
 
+	NameRevCommand setMergeCost(int cost) {
+		mergeCost = cost;
+		return this;
+	}
+
 	private void addPrefixes(Map<ObjectId, String> nonCommits,
 			FIFORevQueue pending) throws IOException {
 		if (!prefixes.isEmpty()) {