Make output stream optional in DiffCommand

Use the NullOutputStream.INSTANCE value when the
configured output stream is null or the command is
configured to only show name and status.

Also only set the context and prefix options if
formatting is actually being performed.

Bug: 377157
Change-Id: I333cfcc82ee746f3c6a8e94c09dcc803ffbb4b3a
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/DiffCommandTest.java

@@ -43,6 +43,8 @@
 package org.eclipse.jgit.api;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
 
 import java.io.ByteArrayOutputStream;
 import java.io.File;
@@ -222,6 +224,23 @@ public class DiffCommandTest extends RepositoryTestCase {
 		assertEquals(expected.toString(), actual);
 	}
 
+	@Test
+	public void testNoOutputStreamSet() throws Exception {
+		File file = writeTrashFile("test.txt", "a");
+		assertTrue(file.setLastModified(file.lastModified() - 5000));
+		Git git = new Git(db);
+		git.add().addFilepattern(".").call();
+		write(file, "b");
+
+		List<DiffEntry> diffs = git.diff().call();
+		assertNotNull(diffs);
+		assertEquals(1, diffs.size());
+		DiffEntry diff = diffs.get(0);
+		assertEquals(ChangeType.MODIFY, diff.getChangeType());
+		assertEquals("test.txt", diff.getOldPath());
+		assertEquals("test.txt", diff.getNewPath());
+	}
+
 	private AbstractTreeIterator getTreeIterator(String name)
 			throws IOException {
 		final ObjectId id = db.resolve(name);

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

@@ -64,6 +64,7 @@ import org.eclipse.jgit.treewalk.AbstractTreeIterator;
 import org.eclipse.jgit.treewalk.CanonicalTreeParser;
 import org.eclipse.jgit.treewalk.FileTreeIterator;
 import org.eclipse.jgit.treewalk.filter.TreeFilter;
+import org.eclipse.jgit.util.io.NullOutputStream;
 
 /**
  * Show changes between commits, commit and working tree, etc.
@@ -108,8 +109,11 @@ public class DiffCommand extends GitCommand<List<DiffEntry>> {
 	 * @return a DiffEntry for each path which is different
 	 */
 	public List<DiffEntry> call() throws GitAPIException, IOException {
-		final DiffFormatter diffFmt = new DiffFormatter(
+		final DiffFormatter diffFmt;
-				new BufferedOutputStream(out));
+		if (out != null && !showNameAndStatusOnly)
+			diffFmt = new DiffFormatter(new BufferedOutputStream(out));
+		else
+			diffFmt = new DiffFormatter(NullOutputStream.INSTANCE);
 		diffFmt.setRepository(repo);
 		diffFmt.setProgressMonitor(monitor);
 		try {
@@ -136,17 +140,17 @@ public class DiffCommand extends GitCommand<List<DiffEntry>> {
 			}
 
 			diffFmt.setPathFilter(pathFilter);
+
+			List<DiffEntry> result = diffFmt.scan(oldTree, newTree);
+			if (showNameAndStatusOnly)
+				return result;
+			else {
 				if (contextLines >= 0)
 					diffFmt.setContext(contextLines);
 				if (destinationPrefix != null)
 					diffFmt.setNewPrefix(destinationPrefix);
 				if (sourcePrefix != null)
 					diffFmt.setOldPrefix(sourcePrefix);
-
-			List<DiffEntry> result = diffFmt.scan(oldTree, newTree);
-			if (showNameAndStatusOnly) {
-				return result;
-			} else {
 				diffFmt.format(result);
 				diffFmt.flush();
 				return result;