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>

8 files changed, 6 insertions, 13 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/AddCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/AddCommand.java
index 12a5201f6e..fcc58d1791 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/AddCommand.java
+++ b/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);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/diff/DiffFormatter.java b/org.eclipse.jgit/src/org/eclipse/jgit/diff/DiffFormatter.java
index fa0cb9c473..adcf0d8d60 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/diff/DiffFormatter.java
+++ b/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);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheBuilder.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheBuilder.java
index 5665002dc7..ed09de3322 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheBuilder.java
+++ b/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);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java
index 11003ff4f0..01cecf40f8 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java
+++ b/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()));
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java
index b9291f11dd..d0ef337035 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java
+++ b/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)
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
index 135597f659..4cf57e8400 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
+++ b/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]);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategySimpleTwoWayInCore.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategySimpleTwoWayInCore.java
index b8bd4758c0..adb2278d89 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategySimpleTwoWayInCore.java
+++ b/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]);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/TreeWalk.java b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/TreeWalk.java
index 992928bc43..93ca33e4c9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/TreeWalk.java
+++ b/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;