Revert "RevWalk: stop mixing lines of history in topo sort"

This reverts commit b5e764abd2.

PlotWalk uses the TopoSortGenerator, which is causing problems for EGit users
who rely on the emission of commits being somewhat based on date as in the
previous topo-sort algorithm.

Bug: 560529
Change-Id: I3dbd3598a7aeb960de3fc39352699b4f11a8c226
Signed-off-by: Alex Spradlin <alexaspradlin@google.com>

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

@@ -563,10 +563,10 @@ public class RebaseCommandTest extends RepositoryTestCase {
 			RevCommit newD = rw.next();
 			assertDerivedFrom(newD, d);
 			assertEquals(2, newD.getParentCount());
-			RevCommit newE = rw.next();
-			assertEquals(e, newE);
 			RevCommit newC = rw.next();
 			assertDerivedFrom(newC, c);
+			RevCommit newE = rw.next();
+			assertEquals(e, newE);
 			assertEquals(newC, newD.getParent(0));
 			assertEquals(e, newD.getParent(1));
 			assertEquals(g, rw.next());

org.eclipse.jgit.test/tst/org/eclipse/jgit/revplot/PlotCommitListTest.java

@@ -254,12 +254,12 @@ public class PlotCommitListTest extends RevWalkTestCase {
 			int posI = test.commit(i).lanePos(childPositions).parents(h)
 					.getLanePos();
 			test.commit(h).lanePos(posI).parents(f);
+			test.commit(g).lanePos(childPositions).parents(a);
 			test.commit(f).lanePos(posI).parents(e, d);
-			test.commit(d).lanePos(1).parents(b);
 			test.commit(e).lanePos(posI).parents(c);
+			test.commit(d).lanePos(2).parents(b);
 			test.commit(c).lanePos(posI).parents(b);
 			test.commit(b).lanePos(posI).parents(a);
-			test.commit(g).lanePos(childPositions).parents(a);
 			test.commit(a).lanePos(0).parents();
 		}
 	}
@@ -325,42 +325,42 @@ public class PlotCommitListTest extends RevWalkTestCase {
 					.lanePos(mainPos);
 			test.commit(merge_update_eclipse)
 					.parents(add_a_clear, update_eclipse).lanePos(mainPos);
-			test.commit(update_eclipse).parents(add_Maven).lanePos(2);
 			test.commit(add_a_clear).parents(fix_broken).lanePos(mainPos);
 			test.commit(fix_broken).parents(merge_disable_comment)
 					.lanePos(mainPos);
 			test.commit(merge_disable_comment)
 					.parents(merge_resolve_handler, disable_comment)
 					.lanePos(mainPos);
-			test.commit(disable_comment).parents(clone_operation).lanePos(3);
+			test.commit(disable_comment).parents(clone_operation).lanePos(2);
 			test.commit(merge_resolve_handler)
 					.parents(clone_operation, resolve_handler).lanePos(mainPos);
-			test.commit(resolve_handler).parents(merge_fix).lanePos(4);
+			test.commit(update_eclipse).parents(add_Maven).lanePos(3);
 			test.commit(clone_operation).parents(merge_changeset_implementation)
 					.lanePos(mainPos);
 			test.commit(merge_changeset_implementation)
 					.parents(merge_disable_source, changeset_implementation)
 					.lanePos(mainPos);
-			test.commit(changeset_implementation).parents(clear_repositorycache)
-					.lanePos(1);
 			test.commit(merge_disable_source)
 					.parents(update_eclipse_iplog2, disable_source)
 					.lanePos(mainPos);
-			test.commit(disable_source).parents(merge_use_remote).lanePos(3);
 			test.commit(update_eclipse_iplog2).parents(merge_use_remote)
 					.lanePos(mainPos);
+			test.commit(disable_source).parents(merge_use_remote).lanePos(1);
 			test.commit(merge_use_remote)
 					.parents(update_eclipse_iplog, use_remote).lanePos(mainPos);
-			test.commit(use_remote).parents(clear_repositorycache).lanePos(3);
+			test.commit(changeset_implementation).parents(clear_repositorycache)
+					.lanePos(2);
 			test.commit(update_eclipse_iplog).parents(merge_add_Maven)
 					.lanePos(mainPos);
 			test.commit(merge_add_Maven).parents(findToolBar_layout, add_Maven)
 					.lanePos(mainPos);
-			test.commit(add_Maven).parents(clear_repositorycache).lanePos(2);
 			test.commit(findToolBar_layout).parents(clear_repositorycache)
 					.lanePos(mainPos);
+			test.commit(use_remote).parents(clear_repositorycache).lanePos(1);
+			test.commit(add_Maven).parents(clear_repositorycache).lanePos(3);
 			test.commit(clear_repositorycache).parents(merge_remove)
 					.lanePos(mainPos);
+			test.commit(resolve_handler).parents(merge_fix).lanePos(4);
 			test.commit(merge_remove).parents(add_simple, remove_unused)
 					.lanePos(mainPos);
 			test.commit(remove_unused).parents(merge_fix).lanePos(1);
@@ -453,36 +453,33 @@ public class PlotCommitListTest extends RevWalkTestCase {
 			pcl.source(pw);
 			pcl.fillTo(Integer.MAX_VALUE);
 
-			Set<Integer> positions = asSet(0, 1);
-			CommitListAssert test = new CommitListAssert(pcl);
-			int posA = test.commit(a5).lanePos(positions).getLanePos();
-			test.commit(a4);
-			test.commit(a3).lanePos(posA);
-			test.commit(e);
-			test.commit(d);
-			test.commit(a2).lanePos(posA);
-			int posB = test.commit(b3).lanePos(positions).getLanePos();
-			test.commit(b2).lanePos(posB);
-			test.commit(b1).lanePos(posB);
-			test.commit(c);
-			test.commit(a1).lanePos(posA);
-			test.noMoreCommits();
-			assertNotEquals("a lane is the same as b lane", posA, posB);
+			// test that the commits b1, b2 and b3 are on the same position
+			int bPos = pcl.get(9).lane.position; // b1
+			assertEquals("b2 is an a different position", bPos,
+					pcl.get(7).lane.position);
+			assertEquals("b3 is on a different position", bPos,
+					pcl.get(4).lane.position);
+
+			// test that nothing blocks the connections between b1, b2 and b3
+			assertNotEquals("b lane is blocked by c", bPos,
+					pcl.get(8).lane.position);
+			assertNotEquals("b lane is blocked by a2", bPos,
+					pcl.get(6).lane.position);
+			assertNotEquals("b lane is blocked by d", bPos,
+					pcl.get(5).lane.position);
 		}
 	}
 
 	/**
 	 * <pre>
 	 *    b3
-	 * a5 |
-	 * |  |
 	 * a4 |
 	 * | \|
 	 * |  b2
 	 * a3 |
 	 * | \|
-	 * |  b1
 	 * a2 |
+	 * |  b1
 	 * | /
 	 * a1
 	 * </pre>
@@ -497,11 +494,10 @@ public class PlotCommitListTest extends RevWalkTestCase {
 		final RevCommit a3 = commit(a2, b1);
 		final RevCommit b2 = commit(b1);
 		final RevCommit a4 = commit(a3, b2);
-		final RevCommit a5 = commit(a4);
 		final RevCommit b3 = commit(b2);
 
 		try (PlotWalk pw = new PlotWalk(db)) {
-			pw.markStart(pw.lookupCommit(a5));
+			pw.markStart(pw.lookupCommit(a4));
 			pw.markStart(pw.lookupCommit(b3));
 			PlotCommitList<PlotLane> pcl = new PlotCommitList<>();
 			pcl.source(pw);
@@ -510,12 +506,11 @@ public class PlotCommitListTest extends RevWalkTestCase {
 			Set<Integer> positions = asSet(0, 1);
 			CommitListAssert test = new CommitListAssert(pcl);
 			int posB = test.commit(b3).lanePos(positions).getLanePos();
-			int posA = test.commit(a5).lanePos(positions).getLanePos();
-			test.commit(a4).lanePos(posA);
+			int posA = test.commit(a4).lanePos(positions).getLanePos();
 			test.commit(b2).lanePos(posB);
 			test.commit(a3).lanePos(posA);
-			test.commit(b1).lanePos(posB);
 			test.commit(a2).lanePos(posA);
+			test.commit(b1).lanePos(posB);
 			test.commit(a1).lanePos(posA);
 			test.noMoreCommits();
 		}
@@ -524,17 +519,13 @@ public class PlotCommitListTest extends RevWalkTestCase {
 	/**
 	 * <pre>
 	 * a4
-	 * |
-	 * a3
-	 * | \\
-	 * a2  \\
-	 * |    \\
-	 * |  b3 ||
-	 * |  |  ||
+	 * |   b3
+	 * a3  |
+	 * | \\|
+	 * |   |\\
 	 * |   b2||
-	 * |  | //
+	 * a2  | //
 	 * |   b1
-	 * |  |
 	 * | /
 	 * a1
 	 * </pre>
@@ -561,10 +552,10 @@ public class PlotCommitListTest extends RevWalkTestCase {
 			Set<Integer> positions = asSet(0, 1);
 			CommitListAssert test = new CommitListAssert(pcl);
 			int posA = test.commit(a4).lanePos(positions).getLanePos();
-			test.commit(a3).lanePos(posA);
-			test.commit(a2).lanePos(posA);
 			int posB = test.commit(b3).lanePos(positions).getLanePos();
+			test.commit(a3).lanePos(posA);
 			test.commit(b2).lanePos(posB);
+			test.commit(a2).lanePos(posA);
 			// b1 is not repositioned, uses "detour lane"
 			// (drawn as a double arc in the ascii graph above)
 			test.commit(b1).lanePos(posB);
@@ -578,14 +569,13 @@ public class PlotCommitListTest extends RevWalkTestCase {
 	 *      b2
 	 * a4   |
 	 * |  \ |
-	 * |    b1
-	 * a3   |
+	 * a3  \|
 	 * | \  |
 	 * |  c |
 	 * | /  |
 	 * a2   |
-	 * |    |
-	 * |   /
+	 * |    b1
+	 *     /
 	 * |  /
 	 * a1
 	 * </pre>
@@ -614,10 +604,10 @@ public class PlotCommitListTest extends RevWalkTestCase {
 			CommitListAssert test = new CommitListAssert(pcl);
 			int posB = test.commit(b2).lanePos(positions).getLanePos();
 			int posA = test.commit(a4).lanePos(positions).getLanePos();
-			test.commit(b1).lanePos(posB); // repositioned to go around c
 			test.commit(a3).lanePos(posA);
 			test.commit(c).lanePos(positions);
 			test.commit(a2).lanePos(posA);
+			test.commit(b1).lanePos(posB); // repositioned to go around c
 			test.commit(a1).lanePos(posA);
 			test.noMoreCommits();
 		}

org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/RevWalkSortTest.java

@@ -144,110 +144,4 @@ public class RevWalkSortTest extends RevWalkTestCase {
 		assertCommit(d, rw.next());
 		assertNull(rw.next());
 	}
-
-        @Test
-	public void testSort_TOPO_OutOfOrderCommitTimes() throws Exception {
-		// b is committed before c2 in a different line of history.
-		//
-		final RevCommit a = commit();
-		final RevCommit c1 = commit(a);
-		final RevCommit b = commit(a);
-		final RevCommit c2 = commit(c1);
-		final RevCommit d = commit(b, c2);
-
-		rw.sort(RevSort.TOPO);
-		markStart(d);
-		assertCommit(d, rw.next());
-		assertCommit(c2, rw.next());
-		assertCommit(c1, rw.next());
-		assertCommit(b, rw.next());
-		assertCommit(a, rw.next());
-		assertNull(rw.next());
-	}
-
-	@Test
-	public void testSort_TOPO_MultipleLinesOfHistory() throws Exception {
-		final RevCommit a1 = commit();
-		final RevCommit b1 = commit(a1);
-		final RevCommit a2 = commit(a1, b1);
-		final RevCommit b2 = commit(b1);
-		final RevCommit b3 = commit(b1);
-		final RevCommit a3 = commit(a2, b2);
-		final RevCommit a4 = commit(a3, b3);
-
-		rw.sort(RevSort.TOPO);
-		markStart(a4);
-		assertCommit(a4, rw.next());
-		assertCommit(b3, rw.next());
-		assertCommit(a3, rw.next());
-		assertCommit(b2, rw.next());
-		assertCommit(a2, rw.next());
-		assertCommit(b1, rw.next());
-		assertCommit(a1, rw.next());
-		assertNull(rw.next());
-	}
-
-	@Test
-	public void testSort_TOPO_REVERSE_MultipleLinesOfHistory()
-			throws Exception {
-		final RevCommit a1 = commit();
-		final RevCommit b1 = commit(a1);
-		final RevCommit a2 = commit(a1, b1);
-		final RevCommit b2 = commit(b1);
-		final RevCommit b3 = commit(b1);
-		final RevCommit a3 = commit(a2, b2);
-		final RevCommit a4 = commit(a3, b3);
-
-		rw.sort(RevSort.TOPO);
-		rw.sort(RevSort.REVERSE, true);
-		markStart(a4);
-		assertCommit(a1, rw.next());
-		assertCommit(b1, rw.next());
-		assertCommit(a2, rw.next());
-		assertCommit(b2, rw.next());
-		assertCommit(a3, rw.next());
-		assertCommit(b3, rw.next());
-		assertCommit(a4, rw.next());
-		assertNull(rw.next());
-	}
-
-	@Test
-	public void testSort_TOPO_ParentOfMultipleStartChildren() throws Exception {
-		final RevCommit a = commit();
-		final RevCommit b = commit(a);
-		final RevCommit c = commit(a);
-		final RevCommit d1 = commit(a);
-		final RevCommit d2 = commit(d1);
-		final RevCommit e = commit(a);
-
-		rw.sort(RevSort.TOPO);
-		markStart(b);
-		markStart(c);
-		markStart(d2);
-		markStart(e);
-		assertCommit(e, rw.next());
-		assertCommit(d2, rw.next());
-		assertCommit(d1, rw.next());
-		assertCommit(c, rw.next());
-		assertCommit(b, rw.next());
-		assertCommit(a, rw.next());
-		assertNull(rw.next());
-	}
-
-	@Test
-	public void testSort_TOPO_Uninteresting() throws Exception {
-		final RevCommit a1 = commit();
-		final RevCommit a2 = commit(a1);
-		final RevCommit a3 = commit(a2);
-		final RevCommit b = commit(a1);
-		final RevCommit a4 = commit(a3, b);
-
-		rw.sort(RevSort.TOPO);
-		markStart(a4);
-		markUninteresting(a2);
-		assertCommit(a4, rw.next());
-		assertCommit(b, rw.next());
-		assertCommit(a3, rw.next());
-		assertNull(rw.next());
-	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevObject.java

@@ -151,7 +151,7 @@ public abstract class RevObject extends ObjectIdOwnerMap.Entry {
 	 *            buffer to append a debug description of core RevFlags onto.
 	 */
 	protected void appendCoreFlags(StringBuilder s) {
-		s.append((flags & RevWalk.TOPO_QUEUED) != 0 ? 'o' : '-');
+		s.append((flags & RevWalk.TOPO_DELAY) != 0 ? 'o' : '-');
 		s.append((flags & RevWalk.TEMP_MARK) != 0 ? 't' : '-');
 		s.append((flags & RevWalk.REWRITE) != 0 ? 'r' : '-');
 		s.append((flags & RevWalk.UNINTERESTING) != 0 ? 'u' : '-');

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalk.java

@@ -125,11 +125,11 @@ public class RevWalk implements Iterable<RevCommit>, AutoCloseable {
 	/**
 	 * Temporary mark for use within {@link TopoSortGenerator}.
 	 * <p>
-	 * This mark indicates the commit has been queued for emission in
-	 * {@link TopoSortGenerator} and can be produced. This mark is removed when
-	 * the commit has been produced.
+	 * This mark indicates the commit could not produce when it wanted to, as at
+	 * least one child was behind it. Commits with this flag are delayed until
+	 * all children have been output first.
 	 */
-	static final int TOPO_QUEUED = 1 << 5;
+	static final int TOPO_DELAY = 1 << 5;
 
 	/** Number of flag bits we keep internal for our own use. See above flags. */
 	static final int RESERVED_FLAGS = 6;

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/TopoSortGenerator.java

@@ -17,7 +17,7 @@ import org.eclipse.jgit.errors.MissingObjectException;
 
 /** Sorts commits in topological order. */
 class TopoSortGenerator extends Generator {
-	private static final int TOPO_QUEUED = RevWalk.TOPO_QUEUED;
+	private static final int TOPO_DELAY = RevWalk.TOPO_DELAY;
 
 	private final FIFORevQueue pending;
 
@@ -47,16 +47,12 @@ class TopoSortGenerator extends Generator {
 			if (c == null) {
 				break;
 			}
-			if ((c.flags & TOPO_QUEUED) == 0) {
 			for (RevCommit p : c.parents) {
 				p.inDegree++;
-
 				if (firstParent) {
 					break;
 				}
 			}
-			}
-			c.flags |= TOPO_QUEUED;
 			pending.add(c);
 		}
 	}
@@ -75,42 +71,34 @@ class TopoSortGenerator extends Generator {
 	RevCommit next() throws MissingObjectException,
 			IncorrectObjectTypeException, IOException {
 		for (;;) {
-			RevCommit c = pending.next();
-			if (c == null) {
+			final RevCommit c = pending.next();
+			if (c == null)
 				return null;
-			}
 
 			if (c.inDegree > 0) {
 				// At least one of our children is missing. We delay
 				// production until all of our children are output.
 				//
+				c.flags |= TOPO_DELAY;
 				continue;
 			}
 
-			if ((c.flags & TOPO_QUEUED) == 0) {
-				// c is a parent that already produced or a parent that
-				// was never in the priority queue and should never produce.
+			// All of our children have already produced,
+			// so it is OK for us to produce now as well.
 			//
-				continue;
-			}
-
 			for (RevCommit p : c.parents) {
-				if (--p.inDegree == 0 && (p.flags & TOPO_QUEUED) != 0) {
-					// The parent has no unproduced interesting children. unpop
-					// the parent so it goes right behind this child. This means
-					// that this parent commit may appear in "pending" more than
-					// once, but this is safe since upon the second and
-					// subsequent iterations with this commit, it will no longer
-					// have TOPO_QUEUED set, and thus will be skipped.
+				if (--p.inDegree == 0 && (p.flags & TOPO_DELAY) != 0) {
+					// This parent tried to come before us, but we are
+					// his last child. unpop the parent so it goes right
+					// behind this child.
 					//
+					p.flags &= ~TOPO_DELAY;
 					pending.unpop(p);
 				}
 				if (firstParent) {
 					break;
 				}
 			}
-
-			c.flags &= ~TOPO_QUEUED;
 			return c;
 		}
 	}