Remove empty iterator from TreeWalk

Its confusing that a new TreeWalk() needs to have reset() invoked
on it before addTree().  This is a historical accident caused by
how TreeWalk was abused within ObjectWalk.

Drop the initial empty tree from the TreeWalk and thus remove a
number of pointless reset() operations from unit tests and some of
the internal JGit code.

Existing application code which is still calling reset() will simply
be incurring a few unnecessary field assignments, but they should
consider cleaning up their code in the future.

Change-Id: I434e94ffa43491019e7dff52ca420a4d2245f48b
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/DiffTree.java

@@ -74,7 +74,6 @@ class DiffTree extends TextBuiltin {
 	@Override
 	protected void run() throws Exception {
 		final TreeWalk walk = new TreeWalk(db);
-		walk.reset();
 		walk.setRecursive(recursive);
 		for (final AbstractTreeIterator i : trees)
 			walk.addTree(i);

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/LsTree.java

@@ -62,7 +62,6 @@ class LsTree extends TextBuiltin {
 	@Override
 	protected void run() throws Exception {
 		final TreeWalk walk = new TreeWalk(db);
-		walk.reset(); // drop the first empty tree, which we do not need here
 		walk.setRecursive(recursive);
 		walk.addTree(tree);
 

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/debug/DiffAlgorithms.java

@@ -59,7 +59,6 @@ import org.eclipse.jgit.diff.RawText;
 import org.eclipse.jgit.diff.RawTextComparator;
 import org.eclipse.jgit.errors.LargeObjectException;
 import org.eclipse.jgit.lib.AbbreviatedObjectId;
-import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.MutableObjectId;
@@ -190,7 +189,7 @@ class DiffAlgorithms extends TextBuiltin {
 
 				RevCommit p = c.getParent(0);
 				rw.parseHeaders(p);
-				tw.reset(new AnyObjectId[] { p.getTree(), c.getTree() });
+				tw.reset(p.getTree(), c.getTree());
 				while (tw.next()) {
 					if (!isFile(tw, 0) || !isFile(tw, 1))
 						continue;

org.eclipse.jgit.test/tst/org/eclipse/jgit/dircache/DirCacheBuilderIteratorTest.java

@@ -71,7 +71,6 @@ public class DirCacheBuilderIteratorTest extends RepositoryTestCase {
 		final int expIdx = 2;
 		final DirCacheBuilder b = dc.builder();
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheBuildIterator(b));
 		tw.setRecursive(true);
 		tw.setFilter(PathFilterGroup.createFromStrings(Collections

org.eclipse.jgit.test/tst/org/eclipse/jgit/dircache/DirCacheCGitCompatabilityTest.java

@@ -90,7 +90,6 @@ public class DirCacheCGitCompatabilityTest extends LocalDiskRepositoryTestCase {
 		{
 			final Iterator<CGitIndexRecord> rItr = ls.values().iterator();
 			final TreeWalk tw = new TreeWalk(db);
-			tw.reset();
 			tw.setRecursive(true);
 			tw.addTree(new DirCacheIterator(dc));
 			while (rItr.hasNext()) {

org.eclipse.jgit.test/tst/org/eclipse/jgit/dircache/DirCacheIteratorTest.java

@@ -64,7 +64,6 @@ public class DirCacheIteratorTest extends RepositoryTestCase {
 		assertEquals(0, dc.getEntryCount());
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(dc));
 		assertFalse(tw.next());
 	}
@@ -112,7 +111,6 @@ public class DirCacheIteratorTest extends RepositoryTestCase {
 
 		final DirCacheIterator i = new DirCacheIterator(dc);
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(i);
 		int pathIdx = 0;
 		while (tw.next()) {
@@ -149,7 +147,6 @@ public class DirCacheIteratorTest extends RepositoryTestCase {
 
 		final DirCacheIterator i = new DirCacheIterator(dc);
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(i);
 		tw.setRecursive(false);
 		int pathIdx = 0;
@@ -189,7 +186,6 @@ public class DirCacheIteratorTest extends RepositoryTestCase {
 
 		final DirCacheIterator i = new DirCacheIterator(dc);
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(i);
 		tw.setRecursive(true);
 		int pathIdx = 0;
@@ -223,7 +219,6 @@ public class DirCacheIteratorTest extends RepositoryTestCase {
 		b.finish();
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(dc));
 		tw.setRecursive(true);
 		int pathIdx = 0;

org.eclipse.jgit.test/tst/org/eclipse/jgit/ignore/IgnoreNodeTest.java

@@ -158,7 +158,6 @@ public class IgnoreNodeTest extends RepositoryTestCase {
 
 	private void beginWalk() throws CorruptObjectException {
 		walk = new TreeWalk(db);
-		walk.reset();
 		walk.addTree(new FileTreeIterator(db));
 	}
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/RacyGitTests.java

@@ -77,7 +77,6 @@ public class RacyGitTests extends RepositoryTestCase {
 		FileTreeIteratorWithTimeControl fileIt = new FileTreeIteratorWithTimeControl(
 				db, modTimes);
 		NameConflictTreeWalk tw = new NameConflictTreeWalk(db);
-		tw.reset();
 		tw.addTree(fileIt);
 		tw.setRecursive(true);
 		FileTreeIterator t;

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ReadTreeTest.java

@@ -685,7 +685,6 @@ public abstract class ReadTreeTest extends RepositoryTestCase {
 	public void assertWorkDir(HashMap<String, String> i)
 			throws CorruptObjectException, IOException {
 		TreeWalk walk = new TreeWalk(db);
-		walk.reset();
 		walk.setRecursive(true);
 		walk.addTree(new FileTreeIterator(db));
 		String expectedValue;

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/NameConflictTreeWalkTest.java

@@ -82,7 +82,6 @@ public class NameConflictTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(tree0));
 		tw.addTree(new DirCacheIterator(tree1));
 
@@ -113,7 +112,6 @@ public class NameConflictTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final NameConflictTreeWalk tw = new NameConflictTreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(tree0));
 		tw.addTree(new DirCacheIterator(tree1));
 
@@ -149,7 +147,6 @@ public class NameConflictTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final NameConflictTreeWalk tw = new NameConflictTreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(tree0));
 		tw.addTree(new DirCacheIterator(tree1));
 
@@ -185,7 +182,6 @@ public class NameConflictTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final NameConflictTreeWalk tw = new NameConflictTreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(tree0));
 		tw.addTree(new DirCacheIterator(tree1));
 
@@ -222,7 +218,6 @@ public class NameConflictTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final NameConflictTreeWalk tw = new NameConflictTreeWalk(db);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(tree0));
 		tw.addTree(new DirCacheIterator(tree1));
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/PostOrderTreeWalkTest.java

@@ -98,7 +98,6 @@ public class PostOrderTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.setPostOrderTraversal(false);
 		tw.addTree(new DirCacheIterator(tree));
 
@@ -127,7 +126,6 @@ public class PostOrderTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.setPostOrderTraversal(true);
 		tw.addTree(new DirCacheIterator(tree));
 
@@ -162,7 +160,6 @@ public class PostOrderTreeWalkTest extends RepositoryTestCase {
 		}
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset();
 		tw.setPostOrderTraversal(true);
 		tw.addTree(new DirCacheIterator(tree));
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/TreeWalkBasicDiffTest.java

@@ -105,7 +105,7 @@ public class TreeWalkBasicDiffTest extends RepositoryTestCase {
 		inserter.release();
 
 		final TreeWalk tw = new TreeWalk(db);
-		tw.reset(new ObjectId[] { oldTree, newTree });
+		tw.reset(oldTree, newTree);
 		tw.setRecursive(true);
 		tw.setFilter(TreeFilter.ANY_DIFF);
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/filter/TreeFilterTest.java

@@ -44,11 +44,13 @@
 package org.eclipse.jgit.treewalk.filter;
 
 import org.eclipse.jgit.lib.RepositoryTestCase;
+import org.eclipse.jgit.treewalk.EmptyTreeIterator;
 import org.eclipse.jgit.treewalk.TreeWalk;
 
 public class TreeFilterTest extends RepositoryTestCase {
 	public void testALL_IncludesAnything() throws Exception {
 		final TreeWalk tw = new TreeWalk(db);
+		tw.addTree(new EmptyTreeIterator());
 		assertTrue(TreeFilter.ALL.include(tw));
 	}
 
@@ -62,11 +64,13 @@ public class TreeFilterTest extends RepositoryTestCase {
 
 	public void testNotALL_IncludesNothing() throws Exception {
 		final TreeWalk tw = new TreeWalk(db);
+		tw.addTree(new EmptyTreeIterator());
 		assertFalse(TreeFilter.ALL.negate().include(tw));
 	}
 
 	public void testANY_DIFF_IncludesSingleTreeCase() throws Exception {
 		final TreeWalk tw = new TreeWalk(db);
+		tw.addTree(new EmptyTreeIterator());
 		assertTrue(TreeFilter.ANY_DIFF.include(tw));
 	}
 

org.eclipse.jgit/src/org/eclipse/jgit/api/AddCommand.java

@@ -138,7 +138,6 @@ public class AddCommand extends GitCommand<DirCache> {
 
 			DirCacheBuilder builder = dc.builder();
 			final TreeWalk tw = new TreeWalk(repo);
-			tw.reset();
 			tw.addTree(new DirCacheBuildIterator(builder));
 			if (workingTreeIterator == null)
 				workingTreeIterator = new FileTreeIterator(repo);

org.eclipse.jgit/src/org/eclipse/jgit/diff/DiffFormatter.java

@@ -431,7 +431,6 @@ public class DiffFormatter {
 		assertHaveRepository();
 
 		TreeWalk walk = new TreeWalk(reader);
-		walk.reset();
 		walk.addTree(a);
 		walk.addTree(b);
 		walk.setRecursive(true);

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheBuilder.java

@@ -165,7 +165,6 @@ public class DirCacheBuilder extends BaseDirCacheEditor {
 	public void addTree(final byte[] pathPrefix, final int stage,
 			final ObjectReader reader, final AnyObjectId tree) throws IOException {
 		final TreeWalk tw = new TreeWalk(reader);
-		tw.reset();
 		tw.addTree(new CanonicalTreeParser(pathPrefix, reader, tree
 				.toObjectId()));
 		tw.setRecursive(true);

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java

@@ -243,7 +243,6 @@ public class DirCacheCheckout {
 		walk = new NameConflictTreeWalk(repo);
 		builder = dc.builder();
 
-		walk.reset();
 		addTree(walk, headCommitTree);
 		addTree(walk, mergeCommitTree);
 		walk.addTree(new DirCacheBuildIterator(builder));
@@ -285,7 +284,6 @@ public class DirCacheCheckout {
 		builder = dc.builder();
 
 		walk = new NameConflictTreeWalk(repo);
-		walk.reset();
 		walk.addTree(mergeCommitTree);
 		walk.addTree(new DirCacheBuildIterator(builder));
 		walk.addTree(workingTree);
@@ -795,7 +793,6 @@ public class DirCacheCheckout {
 
 	private boolean isModified(String path) throws CorruptObjectException, IOException {
 		NameConflictTreeWalk tw = new NameConflictTreeWalk(repo);
-		tw.reset();
 		tw.addTree(new DirCacheIterator(dc));
 		tw.addTree(new FileTreeIterator(repo.getWorkTree(), repo.getFS(),
 				WorkingTreeOptions.createDefaultInstance()));

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

@@ -169,7 +169,6 @@ public class IndexDiff {
 		boolean changesExist = false;
 		DirCache dirCache = repository.readDirCache();
 		TreeWalk treeWalk = new TreeWalk(repository);
-		treeWalk.reset();
 		treeWalk.setRecursive(true);
 		// add the trees (tree, dirchache, workdir)
 		if (tree != null)

org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java

@@ -59,10 +59,10 @@ import java.util.Map;
 
 import org.eclipse.jgit.JGitText;
 import org.eclipse.jgit.diff.DiffAlgorithm;
-import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
 import org.eclipse.jgit.diff.RawText;
 import org.eclipse.jgit.diff.RawTextComparator;
 import org.eclipse.jgit.diff.Sequence;
+import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
 import org.eclipse.jgit.dircache.DirCache;
 import org.eclipse.jgit.dircache.DirCacheBuildIterator;
 import org.eclipse.jgit.dircache.DirCacheBuilder;
@@ -183,7 +183,6 @@ public class ResolveMerger extends ThreeWayMerger {
 			DirCacheBuildIterator buildIt = new DirCacheBuildIterator(builder);
 
 			tw = new NameConflictTreeWalk(db);
-			tw.reset();
 			tw.addTree(mergeBase());
 			tw.addTree(sourceTrees[0]);
 			tw.addTree(sourceTrees[1]);

org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategySimpleTwoWayInCore.java

@@ -112,7 +112,6 @@ public class StrategySimpleTwoWayInCore extends ThreeWayMergeStrategy {
 
 		@Override
 		protected boolean mergeImpl() throws IOException {
-			tw.reset();
 			tw.addTree(mergeBase());
 			tw.addTree(sourceTrees[0]);
 			tw.addTree(sourceTrees[1]);

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/TreeWalk.java

@@ -84,6 +84,8 @@ import org.eclipse.jgit.util.RawParseUtils;
  * permitted, even from concurrent threads.
  */
 public class TreeWalk {
+	private static final AbstractTreeIterator[] NO_TREES = {};
+
 	/**
 	 * Open a tree walk and filter to exactly one path.
 	 * <p>
@@ -226,7 +228,7 @@ public class TreeWalk {
 	public TreeWalk(final ObjectReader or) {
 		reader = or;
 		filter = TreeFilter.ALL;
-		trees = new AbstractTreeIterator[] { new EmptyTreeIterator() };
+		trees = NO_TREES;
 	}
 
 	/** @return the reader this walker is using to load objects. */
@@ -337,7 +339,7 @@ public class TreeWalk {
 
 	/** Reset this walker so new tree iterators can be added to it. */
 	public void reset() {
-		trees = new AbstractTreeIterator[0];
+		trees = NO_TREES;
 		advance = false;
 		depth = 0;
 	}
@@ -400,7 +402,7 @@ public class TreeWalk {
 	 * @throws IOException
 	 *             a loose object or pack file could not be read.
 	 */
-	public void reset(final AnyObjectId[] ids) throws MissingObjectException,
+	public void reset(final AnyObjectId... ids) throws MissingObjectException,
 			IncorrectObjectTypeException, CorruptObjectException, IOException {
 		final int oldLen = trees.length;
 		final int newLen = ids.length;