Allow ObjectWalk to be filtered by an arbitrary predicate

This will make it possible to declare a collection of objects as
ineligible for the walk en masse, for example if they are known to be
uninteresting via a bitmap.

Change-Id: I637008b25bf9fb57df60ebb2133a70214930546a
Signed-off-by: Jonathan Nieder <jrn@google.com>

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

@@ -60,6 +60,7 @@ import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.filter.ObjectFilter;
 import org.eclipse.jgit.util.RawParseUtils;
 
 /**
@@ -99,6 +100,8 @@ public class ObjectWalk extends RevWalk {
 
 	private BlockObjQueue pendingObjects;
 
+	private ObjectFilter objectFilter;
+
 	private TreeVisit freeVisit;
 
 	private TreeVisit currVisit;
@@ -132,6 +135,7 @@ public class ObjectWalk extends RevWalk {
 		setRetainBody(false);
 		rootObjects = new ArrayList<RevObject>();
 		pendingObjects = new BlockObjQueue();
+		objectFilter = ObjectFilter.ALL;
 		pathBuf = new byte[256];
 	}
 
@@ -250,6 +254,38 @@ public class ObjectWalk extends RevWalk {
 		boundary = hasRevSort(RevSort.BOUNDARY);
 	}
 
+	/**
+	 * Get the currently configured object filter.
+	 *
+	 * @return the current filter. Never null as a filter is always needed.
+	 *
+	 * @since 4.1
+	 */
+	public ObjectFilter getObjectFilter() {
+		return objectFilter;
+	}
+
+	/**
+	 * Set the object filter for this walker.  This filter affects the objects
+	 * visited by {@link #nextObject()}.  It does not affect the commits
+	 * listed by {@link #next()}.
+	 * <p>
+	 * If the filter returns false for an object, then that object is skipped
+	 * and objects reachable from it are not enqueued to be walked recursively.
+	 * This can be used to speed up the object walk by skipping subtrees that
+	 * are known to be uninteresting.
+	 *
+	 * @param newFilter
+	 *            the new filter. If null the special {@link ObjectFilter#ALL}
+	 *            filter will be used instead, which as it matches every object.
+	 *
+	 * @since 4.1
+	 */
+	public void setObjectFilter(ObjectFilter newFilter) {
+		assertNotStarted();
+		objectFilter = newFilter != null ? newFilter : ObjectFilter.ALL;
+	}
+
 	@Override
 	public RevCommit next() throws MissingObjectException,
 			IncorrectObjectTypeException, IOException {
@@ -258,13 +294,19 @@ public class ObjectWalk extends RevWalk {
 			if (r == null) {
 				return null;
 			}
+			final RevTree t = r.getTree();
 			if ((r.flags & UNINTERESTING) != 0) {
-				markTreeUninteresting(r.getTree());
-				if (boundary)
+				if (objectFilter.include(this, t)) {
+					markTreeUninteresting(t);
+				}
+				if (boundary) {
 					return r;
+				}
 				continue;
 			}
-			pendingObjects.add(r.getTree());
+			if (objectFilter.include(this, t)) {
+				pendingObjects.add(t);
+			}
 			return r;
 		}
 	}
@@ -296,6 +338,10 @@ public class ObjectWalk extends RevWalk {
 				idBuffer.fromRaw(buf, ptr);
 				ptr += ID_SZ;
 
+				if (!objectFilter.include(this, idBuffer)) {
+					continue;
+				}
+
 				RevObject obj = objects.get(idBuffer);
 				if (obj != null && (obj.flags & SEEN) != 0)
 					continue;

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/filter/ObjectFilter.java

@@ -0,0 +1,87 @@
+/**
+ * Copyright (C) 2015, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.revwalk.filter;
+
+import java.io.IOException;
+
+import org.eclipse.jgit.errors.IncorrectObjectTypeException;
+import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.errors.StopWalkException;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.revwalk.ObjectWalk;
+
+/**
+ * Selects interesting objects when walking.
+ * <p>
+ * Applications should install the filter on an ObjectWalk by
+ * {@link ObjectWalk#setObjectFilter(ObjectFilter)} prior to starting traversal.
+ *
+ * @since 4.1
+ */
+public abstract class ObjectFilter {
+	/** Default filter that always returns true. */
+	public static final ObjectFilter ALL = new AllFilter();
+
+	private static final class AllFilter extends ObjectFilter {
+		@Override
+		public boolean include(ObjectWalk walker, AnyObjectId o) {
+			return true;
+		}
+	}
+
+	/**
+	 * Determine if the named object should be included in the walk.
+	 *
+	 * @param walker
+	 *	      the active walker this filter is being invoked from within.
+	 * @param objid
+	 *	      the object currently being tested.
+	 * @throws IOException
+	 *	      an object the filter needed to consult to determine its answer
+	 *	      was missing, of the wrong type, or could not be read.
+	 */
+	public abstract boolean include(ObjectWalk walker, AnyObjectId objid)
+			throws MissingObjectException, IncorrectObjectTypeException,
+			       IOException;
+}