PackWriterBitmapPreparer: Do not generate bitmaps for excessive branch tips.

In https://review.gerrithub.io/c/eclipse-jgit/jgit/+/1174407, I changed the bitmap selection algorithm to cap the number of branches included in the bitmap.

There was a bug in that change. When the selection algorithm iterates
over the commits in a branch B, it automatically includes a bitmap for
the tip of any other branch C that happens to be on B. So even though we never iterated over C, we would still index the tip commit of C.

Keep a list of the "excessive" branch tips and check that the commit is not in there before generating a bitmap. We only skip tips that would be selected as a result of being a tip.  If it would be selected for some other reason (e.g. it is one of the first 100 commits in master) then it is not skipped.

Change-Id: Ic8b4f82e816eac649a47c8918a41ed4ff0d877cd

1 files changed, 6 insertions, 3 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java
index 0c67b45344..dabc1f0c5f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java
@@ -166,8 +166,11 @@ class PackWriterBitmapPreparer {
 			rw2.setRetainBody(false);
 			rw2.setRevFilter(new NotInBitmapFilter(seen));
 
-			int maxBranches = Math.min(excessiveBranchTipCount,
-					selectionHelper.newWantsByNewest.size());
+			int newWantsCount = selectionHelper.newWantsByNewest.size();
+			int maxBranches = Math.min(excessiveBranchTipCount, newWantsCount);
+			Set<RevCommit> excessiveBranches = new HashSet<>(
+					selectionHelper.newWantsByNewest.subList(maxBranches,
+							newWantsCount));
 			// For each branch, do a revwalk to enumerate its commits. Exclude
 			// both reused commits and any commits seen in a previous branch.
 			// Then iterate through all new commits from oldest to newest,
@@ -229,7 +232,7 @@ class PackWriterBitmapPreparer {
 					pm.update(1);
 
 					// Always pick the items in wants, prefer merge commits.
-					if (selectionHelper.newWants.remove(c)) {
+					if (!excessiveBranches.contains(c) && selectionHelper.newWants.remove(c)) {
 						if (nextIn > 0) {
 							nextFlg = 0;
 						}