DiffFormatter: Use IndexDiffFilter to speed up working tree

If DiffFormatter is asked to compare the index to the working tree,
it can go faster by using the cached stat information to compare
the two entries rather than relying on SHA-1 computation alone.

Change-Id: Icb21c15b8279ee8cee382e5e179e0cf8903aee4d
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

@@ -65,6 +65,7 @@ import java.util.List;
 import org.eclipse.jgit.JGitText;
 import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
 import org.eclipse.jgit.diff.DiffEntry.ChangeType;
+import org.eclipse.jgit.dircache.DirCacheIterator;
 import org.eclipse.jgit.errors.AmbiguousObjectException;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.errors.LargeObjectException;
@@ -91,7 +92,9 @@ import org.eclipse.jgit.treewalk.CanonicalTreeParser;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.eclipse.jgit.treewalk.WorkingTreeIterator;
 import org.eclipse.jgit.treewalk.filter.AndTreeFilter;
+import org.eclipse.jgit.treewalk.filter.IndexDiffFilter;
 import org.eclipse.jgit.treewalk.filter.NotIgnoredFilter;
+import org.eclipse.jgit.treewalk.filter.PathFilter;
 import org.eclipse.jgit.treewalk.filter.TreeFilter;
 import org.eclipse.jgit.util.QuotedString;
 import org.eclipse.jgit.util.io.DisabledOutputStream;
@@ -435,15 +438,14 @@ public class DiffFormatter {
 		walk.addTree(b);
 		walk.setRecursive(true);
 
-		TreeFilter filter = pathFilter;
-
-		if (a instanceof WorkingTreeIterator)
-			filter = AndTreeFilter.create(filter, new NotIgnoredFilter(0));
-		if (b instanceof WorkingTreeIterator)
-			filter = AndTreeFilter.create(filter, new NotIgnoredFilter(1));
-		if (!(pathFilter instanceof FollowFilter))
-			filter = AndTreeFilter.create(filter, TreeFilter.ANY_DIFF);
-		walk.setFilter(filter);
+		TreeFilter filter = getDiffTreeFilterFor(a, b);
+		if (pathFilter instanceof FollowFilter) {
+			walk.setFilter(AndTreeFilter.create(
+					PathFilter.create(((FollowFilter) pathFilter).getPath()),
+					filter));
+		} else {
+			walk.setFilter(AndTreeFilter.create(pathFilter, filter));
+		}
 
 		source = new ContentSource.Pair(source(a), source(b));
 
@@ -458,12 +460,6 @@ public class DiffFormatter {
 			walk.reset();
 			walk.addTree(a);
 			walk.addTree(b);
-
-			filter = TreeFilter.ANY_DIFF;
-			if (a instanceof WorkingTreeIterator)
-				filter = AndTreeFilter.create(new NotIgnoredFilter(0), filter);
-			if (b instanceof WorkingTreeIterator)
-				filter = AndTreeFilter.create(new NotIgnoredFilter(1), filter);
 			walk.setFilter(filter);
 
 			if (renameDetector == null)
@@ -476,6 +472,22 @@ public class DiffFormatter {
 		return files;
 	}
 
+	private static TreeFilter getDiffTreeFilterFor(AbstractTreeIterator a,
+			AbstractTreeIterator b) {
+		if (a instanceof DirCacheIterator && b instanceof WorkingTreeIterator)
+			return new IndexDiffFilter(0, 1);
+
+		if (a instanceof WorkingTreeIterator && b instanceof DirCacheIterator)
+			return new IndexDiffFilter(1, 0);
+
+		TreeFilter filter = TreeFilter.ANY_DIFF;
+		if (a instanceof WorkingTreeIterator)
+			filter = AndTreeFilter.create(new NotIgnoredFilter(0), filter);
+		if (b instanceof WorkingTreeIterator)
+			filter = AndTreeFilter.create(new NotIgnoredFilter(1), filter);
+		return filter;
+	}
+
 	private ContentSource source(AbstractTreeIterator iterator) {
 		if (iterator instanceof WorkingTreeIterator)
 			return ContentSource.create((WorkingTreeIterator) iterator);