RevCommitCG: Read changed-path-filters directly from commit graph

RevCommit and RevCommitCG were designed like "pointers" to data that
load the content on demand, not on construction. This saves memory.

Make the loading of changed-path-filter follow the same pattern. The
ChangedPathFilters are only pointers to locations in the commit-graph
(not the actual data), so the memory saving is not that big, but this
is more consistent with the rest of the API.

As 6.7 is not released, we can still change the RevWalk API.

Change-Id: Id4186ea744b8a2418d0329facae69f785108d356

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/commitgraph/CommitGraphWriter.java

@@ -48,6 +48,7 @@
 import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.ProgressMonitor;
 import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.treewalk.EmptyTreeIterator;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.eclipse.jgit.util.NB;
@@ -405,25 +406,27 @@ private BloomFilterChunks computeBloomFilterChunks(Stats stats)
 		data.write(scratch);
 		int dataHeaderSize = data.size();
 
-		for (RevCommit cmit : graphCommits) {
-			ChangedPathFilter cpf = cmit.getChangedPathFilter();
-			if (cpf != null) {
-				stats.changedPathFiltersReused++;
-			} else {
-				stats.changedPathFiltersComputed++;
-				Optional<HashSet<ByteBuffer>> paths = computeBloomFilterPaths(
-						graphCommits.getObjectReader(), cmit);
-				if (paths.isEmpty()) {
-					cpf = ChangedPathFilter.FULL;
+		try (RevWalk rw = new RevWalk(graphCommits.getObjectReader())) {
+			for (RevCommit cmit : graphCommits) {
+				ChangedPathFilter cpf = cmit.getChangedPathFilter(rw);
+				if (cpf != null) {
+					stats.changedPathFiltersReused++;
 				} else {
-					cpf = ChangedPathFilter.fromPaths(paths.get());
+					stats.changedPathFiltersComputed++;
+					Optional<HashSet<ByteBuffer>> paths = computeBloomFilterPaths(
+							graphCommits.getObjectReader(), cmit);
+					if (paths.isEmpty()) {
+						cpf = ChangedPathFilter.FULL;
+					} else {
+						cpf = ChangedPathFilter.fromPaths(paths.get());
+					}
 				}
+				cpf.writeTo(data);
+				NB.encodeInt32(scratch, 0, data.size() - dataHeaderSize);
+				index.write(scratch);
 			}
-			cpf.writeTo(data);
-			NB.encodeInt32(scratch, 0, data.size() - dataHeaderSize);
-			index.write(scratch);
+			return new BloomFilterChunks(index, data);
 		}
-		return new BloomFilterChunks(index, data);
 	}
 
 	private void writeExtraEdges(CancellableDigestOutputStream out)

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

@@ -694,10 +694,11 @@ int getGeneration() {
 	 * commit graph file, or the commit graph file was generated without changed
 	 * path filters.
 	 *
+	 * @param rw A revwalk to load the commit graph (if available)
 	 * @return the changed path filter
 	 * @since 6.7
 	 */
-	public ChangedPathFilter getChangedPathFilter() {
+	public ChangedPathFilter getChangedPathFilter(RevWalk rw) {
 		return null;
 	}
 

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

@@ -30,8 +30,6 @@ class RevCommitCG extends RevCommit {
 
 	private final int graphPosition;
 
-	private final ChangedPathFilter changedPathFilter;
-
 	private int generation = Constants.COMMIT_GENERATION_UNKNOWN;
 
 	/**
@@ -41,14 +39,10 @@ class RevCommitCG extends RevCommit {
 	 *            object name for the commit.
 	 * @param graphPosition
 	 *            the position in the commit-graph of the object.
-	 * @param changedPathFilter
-	 *            the changed path filter if one exists
 	 */
-	protected RevCommitCG(AnyObjectId id, int graphPosition,
-			ChangedPathFilter changedPathFilter) {
+	protected RevCommitCG(AnyObjectId id, int graphPosition) {
 		super(id);
 		this.graphPosition = graphPosition;
-		this.changedPathFilter = changedPathFilter;
 	}
 
 	@Override
@@ -110,7 +104,7 @@ int getGeneration() {
 
 	/** {@inheritDoc} */
 	@Override
-	public ChangedPathFilter getChangedPathFilter() {
-		return changedPathFilter;
+	public ChangedPathFilter getChangedPathFilter(RevWalk rw) {
+		return rw.commitGraph().getChangedPathFilter(graphPosition);
 	}
 }

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

@@ -1713,8 +1713,7 @@ protected RevCommit createCommit(AnyObjectId id) {
 
 	private RevCommit createCommit(AnyObjectId id, int graphPos) {
 		if (graphPos >= 0) {
-			return new RevCommitCG(id, graphPos,
-					commitGraph().getChangedPathFilter(graphPos));
+			return new RevCommitCG(id, graphPos);
 		}
 		return new RevCommit(id);
 	}

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

@@ -133,7 +133,7 @@ public boolean include(RevWalk walker, RevCommit c)
 			int chgs = 0, adds = 0;
 			boolean changedPathFilterUsed = false;
 			boolean mustCalculateChgs = true;
-			ChangedPathFilter cpf = c.getChangedPathFilter();
+			ChangedPathFilter cpf = c.getChangedPathFilter(walker);
 			if (cpf != null) {
 				Optional<Set<byte[]>> paths = pathFilter.getFilter()
 						.getPathsBestEffort();