ObjectReader: remove the walkAdvice API

This was added a very long time ago to support the failed
DHT storage implementation. Since then no storage system
was able to make use of this API, but it pollutes internals
of the walkers.

Kill the API on ObjectReader and drop the invocations from
the walker code.

Change-Id: I36608afdac13a6c3084d7c7e0af5e0cb22900332

org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectReader.java

 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs;
-import org.eclipse.jgit.revwalk.ObjectWalk;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
 
 /**
  * Reads an {@link ObjectDatabase} for a single thread.
 		};
 	}
 
-	/**
-	 * Advice from a {@link RevWalk} that a walk is starting from these roots.
-	 *
-	 * @param walk
-	 *            the revision pool that is using this reader.
-	 * @param roots
-	 *            starting points of the revision walk. The starting points have
-	 *            their headers parsed, but might be missing bodies.
-	 * @throws IOException
-	 *             the reader cannot initialize itself to support the walk.
-	 */
-	public void walkAdviceBeginCommits(RevWalk walk, Collection<RevCommit> roots)
-			throws IOException {
-		// Do nothing by default, most readers don't want or need advice.
-	}
-
-	/**
-	 * Advice from an {@link ObjectWalk} that trees will be traversed.
-	 *
-	 * @param ow
-	 *            the object pool that is using this reader.
-	 * @param min
-	 *            the first commit whose root tree will be read.
-	 * @param max
-	 *            the last commit whose root tree will be read.
-	 * @throws IOException
-	 *             the reader cannot initialize itself to support the walk.
-	 */
-	public void walkAdviceBeginTrees(ObjectWalk ow, RevCommit min, RevCommit max)
-			throws IOException {
-		// Do nothing by default, most readers don't want or need advice.
-	}
-
-	/** Advice from that a walk is over. */
-	public void walkAdviceEnd() {
-		// Do nothing by default, most readers don't want or need advice.
-	}
-
 	/**
 	 * Advise the reader to avoid unreachable objects.
 	 * <p>

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

 		for (;;) {
 			final RevCommit c = pending.next();
 			if (c == null) {
-				walker.reader.walkAdviceEnd();
 				return null;
 			}
 

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

 
 	private BlockObjQueue pendingObjects;
 
-	private RevCommit firstCommit;
-
-	private RevCommit lastCommit;
-
 	private TreeVisit freeVisit;
 
 	private TreeVisit currVisit;
 		for (;;) {
 			final RevCommit r = super.next();
 			if (r == null) {
-				if (firstCommit != null)
-					reader.walkAdviceBeginTrees(this, firstCommit, lastCommit);
 				return null;
 			}
 			if ((r.flags & UNINTERESTING) != 0) {
 					return r;
 				continue;
 			}
-			if (firstCommit == null)
-				firstCommit = r;
-			lastCommit = r;
 			pendingObjects.add(r.getTree());
 			return r;
 		}
 		for (;;) {
 			RevObject o = pendingObjects.next();
 			if (o == null) {
-				reader.walkAdviceEnd();
 				return null;
 			}
 			int flags = o.flags;
 	public void dispose() {
 		super.dispose();
 		pendingObjects = new BlockObjQueue();
-		firstCommit = null;
-		lastCommit = null;
 		currVisit = null;
 		freeVisit = null;
 	}
 
 		rootObjects = new ArrayList<RevObject>();
 		pendingObjects = new BlockObjQueue();
-		firstCommit = null;
-		lastCommit = null;
 		currVisit = null;
 		freeVisit = null;
 	}

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

 			for (;;) {
 				final RevCommit c = pending.next();
 				if (c == null) {
-					walker.reader.walkAdviceEnd();
 					return null;
 				}
 
 					c.disposeBody();
 			}
 		} catch (StopWalkException swe) {
-			walker.reader.walkAdviceEnd();
 			pending.clear();
 			return null;
 		}

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

 		final TreeFilter tf = w.getTreeFilter();
 		AbstractRevQueue q = walker.queue;
 
-		w.reader.walkAdviceBeginCommits(w, w.roots);
-
 		if (rf == RevFilter.MERGE_BASE) {
 			// Computing for merge bases is a special case and does not
 			// use the bulk of the generator pipeline.