PackWriter: support excluding objects already in other packs

This can be useful when implementing garbage collection and there
are packs that should not be copied, such as huge packs that have
a sibling ".keep" file alongside of them.

Callers driving PackWriter need to initialize the list of packs not
to include objects from by passing each index to excludeObjects().

Change-Id: Id7f34df69df97be406bcae184308e92b0e8690fd
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackWriter.java

@@ -99,6 +99,7 @@ import org.eclipse.jgit.revwalk.RevObject;
 import org.eclipse.jgit.revwalk.RevSort;
 import org.eclipse.jgit.revwalk.RevTag;
 import org.eclipse.jgit.revwalk.RevTree;
+import org.eclipse.jgit.storage.file.PackIndex;
 import org.eclipse.jgit.storage.file.PackIndexWriter;
 import org.eclipse.jgit.util.BlockList;
 import org.eclipse.jgit.util.TemporaryBuffer;
@@ -157,6 +158,10 @@ public class PackWriter {
 
 	private Set<ObjectId> tagTargets = Collections.emptySet();
 
+	private PackIndex[] excludeInPacks;
+
+	private PackIndex excludeInPackLast;
+
 	private Deflater myDeflater;
 
 	private final ObjectReader reader;
@@ -425,6 +430,25 @@ public class PackWriter {
 		return stats.totalObjects;
 	}
 
+	/**
+	 * Add a pack index whose contents should be excluded from the result.
+	 *
+	 * @param idx
+	 *            objects in this index will not be in the output pack.
+	 */
+	public void excludeObjects(PackIndex idx) {
+		if (excludeInPacks == null) {
+			excludeInPacks = new PackIndex[] { idx };
+			excludeInPackLast = idx;
+		} else {
+			int cnt = excludeInPacks.length;
+			PackIndex[] newList = new PackIndex[cnt + 1];
+			System.arraycopy(excludeInPacks, 0, newList, 0, cnt);
+			newList[cnt] = idx;
+			excludeInPacks = newList;
+		}
+	}
+
 	/**
 	 * Prepare the list of objects to be written to the pack stream.
 	 * <p>
@@ -721,6 +745,9 @@ public class PackWriter {
 		if (writeMonitor == null)
 			writeMonitor = NullProgressMonitor.INSTANCE;
 
+		excludeInPacks = null;
+		excludeInPackLast = null;
+
 		boolean needSearchForReuse = reuseSupport != null && (
 				   reuseDeltas
 				|| config.isReuseObjects()
@@ -1459,6 +1486,8 @@ public class PackWriter {
 		BlockList<RevCommit> commits = new BlockList<RevCommit>();
 		RevCommit c;
 		while ((c = walker.next()) != null) {
+			if (exclude(c))
+				continue;
 			if (c.has(inCachedPack)) {
 				CachedPack pack = tipToPack.get(c);
 				if (includesAllTips(pack, include, walker)) {
@@ -1524,6 +1553,8 @@ public class PackWriter {
 			while ((o = walker.nextObject()) != null) {
 				if (o.has(RevFlag.UNINTERESTING))
 					continue;
+				if (exclude(o))
+					continue;
 
 				int pathHash = walker.getPathHashCode();
 				byte[] pathBuf = walker.getPathBuffer();
@@ -1537,6 +1568,8 @@ public class PackWriter {
 			while ((o = walker.nextObject()) != null) {
 				if (o.has(RevFlag.UNINTERESTING))
 					continue;
+				if (exclude(o))
+					continue;
 				addObject(o, walker.getPathHashCode());
 				countingMonitor.update(1);
 			}
@@ -1608,7 +1641,8 @@ public class PackWriter {
 	 */
 	public void addObject(final RevObject object)
 			throws IncorrectObjectTypeException {
-		addObject(object, 0);
+		if (!exclude(object))
+			addObject(object, 0);
 	}
 
 	private void addObject(final RevObject object, final int pathHashCode) {
@@ -1622,6 +1656,20 @@ public class PackWriter {
 		objectsMap.add(otp);
 	}
 
+	private boolean exclude(AnyObjectId objectId) {
+		if (excludeInPacks == null)
+			return false;
+		if (excludeInPackLast.hasObject(objectId))
+			return true;
+		for (PackIndex idx : excludeInPacks) {
+			if (idx.hasObject(objectId)) {
+				excludeInPackLast = idx;
+				return true;
+			}
+		}
+		return false;
+	}
+
 	/**
 	 * Select an object representation for this writer.
 	 * <p>