Fix diff header on renamed or copied files

When git-core renames or copies a file and the mode differs the
header shows the mode change first, then the rename or copy data:

  diff --git a/COPYING b/LICENSE
  old mode 100644
  new mode 100755
  similarity index 92%
  rename from COPYING
  rename to LICENSE
  index d645695..54863be
  --- a/COPYING
  +++ b/LICENSE
  @@ -56,20 +56,6 @@

JGit relies on this ordering inside of FileHeader. Parsing "new file
mode NNN" after "copy from/to" or "rename from/to" resets the change
type to be ADD, losing the COPIED or RENAMED status and old path.

This fixes a 4 year old bug in Gerrit Code Review that prevents
opening a file for review if the file was copied from another file,
modified in this change, and the mode was updated (e.g. execute
bit was added).

Change-Id: If4c9ecd61ef0ca8e3e1ea857301f7b5c948efb96
[ms: added test case]
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/diff/DiffFormatterTest.java

@@ -285,6 +285,29 @@ public class DiffFormatterTest extends RepositoryTestCase {
 		assertEquals(expected, fh.getScriptText());
 	}
 
+	@Test
+	public void testCreateFileHeaderForRenameModeChange()
+			throws Exception {
+		DiffEntry a = DiffEntry.delete(PATH_A, ObjectId.zeroId());
+		DiffEntry b = DiffEntry.add(PATH_B, ObjectId.zeroId());
+		b.oldMode = FileMode.REGULAR_FILE;
+		b.newMode = FileMode.EXECUTABLE_FILE;
+		DiffEntry m = DiffEntry.pair(ChangeType.RENAME, a, b, 100);
+		m.oldId = null;
+		m.newId = null;
+
+		FileHeader fh = df.toFileHeader(m);
+		//@formatter:off
+		String expected = DIFF + "a/src/a b/src/b\n" +
+				"old mode 100644\n" +
+				"new mode 100755\n" +
+				"similarity index 100%\n" +
+				"rename from src/a\n" +
+				"rename to src/b\n";
+		//@formatter:on
+		assertEquals(expected, fh.getScriptText());
+	}
+
 	@Test
 	public void testDiff() throws Exception {
 		write(new File(db.getDirectory().getParent(), "test.txt"), "test");

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

@@ -1044,6 +1044,17 @@ public class DiffFormatter {
 
 		formatGitDiffFirstHeaderLine(o, type, oldp, newp);
 
+		if ((type == MODIFY || type == COPY || type == RENAME)
+				&& !oldMode.equals(newMode)) {
+			o.write(encodeASCII("old mode ")); //$NON-NLS-1$
+			oldMode.copyTo(o);
+			o.write('\n');
+
+			o.write(encodeASCII("new mode ")); //$NON-NLS-1$
+			newMode.copyTo(o);
+			o.write('\n');
+		}
+
 		switch (type) {
 		case ADD:
 			o.write(encodeASCII("new file mode ")); //$NON-NLS-1$
@@ -1077,12 +1088,6 @@ public class DiffFormatter {
 
 			o.write(encode("copy to " + quotePath(newp))); //$NON-NLS-1$
 			o.write('\n');
-
-			if (!oldMode.equals(newMode)) {
-				o.write(encodeASCII("new file mode ")); //$NON-NLS-1$
-				newMode.copyTo(o);
-				o.write('\n');
-			}
 			break;
 
 		case MODIFY:
@@ -1094,16 +1099,6 @@ public class DiffFormatter {
 			break;
 		}
 
-		if ((type == MODIFY || type == RENAME) && !oldMode.equals(newMode)) {
-			o.write(encodeASCII("old mode ")); //$NON-NLS-1$
-			oldMode.copyTo(o);
-			o.write('\n');
-
-			o.write(encodeASCII("new mode ")); //$NON-NLS-1$
-			newMode.copyTo(o);
-			o.write('\n');
-		}
-
 		if (ent.getOldId() != null && !ent.getOldId().equals(ent.getNewId())) {
 			formatIndexLine(o, ent);
 		}