Keep original timestamp on rebase

Squash commits of branch bugfix/keep_original_timestamp_on_rebase:

- Keep original timestamp on rebase

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/CommitHelper.java

@@ -66,12 +66,21 @@ class CommitHelper {
                         String message,
                         boolean sign,
                         ObjectId... parentCommitIds) throws IOException, CanceledException, UnsupportedSigningFormatException {
+    return createCommit(treeId, createPersonIdent(author), committer, message, sign, parentCommitIds);
+  }
+
+  ObjectId createCommit(ObjectId treeId,
+                        PersonIdent author,
+                        Person committer,
+                        String message,
+                        boolean sign,
+                        ObjectId... parentCommitIds) throws IOException, CanceledException, UnsupportedSigningFormatException {
     log.trace("create commit for tree {} and parent ids {} in repository {}", treeId, parentCommitIds, context.getRepository());
     try (ObjectInserter inserter = repository.newObjectInserter()) {
       CommitBuilder commitBuilder = new CommitBuilder();
       commitBuilder.setTreeId(treeId);
       commitBuilder.setParentIds(parentCommitIds);
-      commitBuilder.setAuthor(createPersonIdent(author));
+      commitBuilder.setAuthor(author);
       commitBuilder.setCommitter(createPersonIdent(committer));
       commitBuilder.setMessage(message);
       if (sign) {

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitMergeRebase.java

@@ -85,7 +85,7 @@ class GitMergeRebase {
         PersonIdent originalAuthor = commit.getAuthorIdent();
         targetRevision = commitHelper.createCommit(
           newTreeId,
-          new Person(originalAuthor.getName(), originalAuthor.getEmailAddress()),
+          originalAuthor,
           request.getAuthor(),
           commit.getFullMessage(),
           request.isSign(),

scm-plugins/scm-git-plugin/src/test/java/sonia/scm/repository/spi/GitMergeCommandTest.java

@@ -543,6 +543,7 @@ public class GitMergeCommandTest extends AbstractGitCommandTestBase {
     assertThat(mergeCommit.getParent(0).name()).isEqualTo("fcd0ef1831e4002ac43ea539f4094334c79ea9ec");
     assertThat(mergeCommit.getName()).isEqualTo(mergeCommandResult.getNewHeadRevision());
     assertThat(mergeCommit.getName()).doesNotStartWith("91b99de908fcd04772798a31c308a64aea1a5523");
+    assertThat(mergeCommit.getAuthorIdent().getWhenAsInstant()).isEqualTo("2018-11-07T10:20:52Z"); // the timestamp of the original commit
   }
 
   @Test