RepoCommand: don't record new commit if tree did not change

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Change-Id: Ib6509e816684256d723558d5e8f3c37de58a2ff8

org.eclipse.jgit.test/tst/org/eclipse/jgit/gitrepo/RepoCommandTest.java

@@ -185,6 +185,59 @@ public class RepoCommandTest extends RepositoryTestCase {
 		}
 	}
 
+	@Test
+	public void runTwiceIsNOP() throws Exception {
+		Repository child = Git.cloneRepository()
+			.setURI(groupADb.getDirectory().toURI().toString())
+			.setDirectory(createUniqueTestGitDir(true)).setBare(true).call()
+			.getRepository();
+
+		Repository dest = Git.cloneRepository()
+			.setURI(db.getDirectory().toURI().toString())
+			.setDirectory(createUniqueTestGitDir(true)).setBare(true).call()
+			.getRepository();
+
+		assertTrue(dest.isBare());
+		assertTrue(child.isBare());
+
+		StringBuilder xmlContent = new StringBuilder();
+		xmlContent.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n")
+			.append("<manifest>")
+			.append("<remote name=\"remote1\" fetch=\"..\" />")
+			.append("<default revision=\"master\" remote=\"remote1\" />")
+			.append("<project path=\"base\" name=\"platform/base\" />")
+			.append("</manifest>");
+		RepoCommand cmd = new RepoCommand(dest);
+
+		IndexedRepos repos = new IndexedRepos();
+		repos.put("platform/base", child);
+
+		RevCommit commit = cmd
+			.setInputStream(new ByteArrayInputStream(
+				xmlContent.toString().getBytes(UTF_8)))
+			.setRemoteReader(repos)
+			.setURI("platform/")
+			.setTargetURI("platform/superproject")
+			.setRecordRemoteBranch(true)
+			.setRecordSubmoduleLabels(true)
+			.call();
+
+		String firstIdStr = commit.getId().name() + ":" + ".gitmodules";
+		commit = new RepoCommand(dest)
+			.setInputStream(new ByteArrayInputStream(
+				xmlContent.toString().getBytes(UTF_8)))
+			.setRemoteReader(repos)
+			.setURI("platform/")
+			.setTargetURI("platform/superproject")
+			.setRecordRemoteBranch(true)
+			.setRecordSubmoduleLabels(true)
+			.call();
+		String idStr = commit.getId().name() + ":" + ".gitmodules";
+		assertEquals(firstIdStr, idStr);
+		child.close();
+		dest.close();
+	}
+
 	@Test
 	public void androidSetup() throws Exception {
 		Repository child = Git.cloneRepository()
@@ -235,6 +288,7 @@ public class RepoCommandTest extends RepositoryTestCase {
 		child.close();
 		dest.close();
 	}
+
 	@Test
 	public void recordUnreachableRemotes() throws Exception {
 		StringBuilder xmlContent = new StringBuilder();
@@ -277,8 +331,6 @@ public class RepoCommandTest extends RepositoryTestCase {
 		dest.close();
 	}
 
-
-
 	@Test
 	public void gerritSetup() throws Exception {
 		Repository child =

org.eclipse.jgit/src/org/eclipse/jgit/gitrepo/RepoCommand.java

@@ -643,6 +643,11 @@ public class RepoCommand extends GitCommand<RevCommit> {
 
 				// Create a Commit object, populate it and write it
 				ObjectId headId = repo.resolve(targetBranch + "^{commit}"); //$NON-NLS-1$
+				if (headId != null && rw.parseCommit(headId).getTree().getId().equals(treeId)) {
+					// No change. Do nothing.
+					return rw.parseCommit(headId);
+				}
+
 				CommitBuilder commit = new CommitBuilder();
 				commit.setTreeId(treeId);
 				if (headId != null)