Rebase: Improve error message when rebasing a change onto itself

Change it from:

 "cannot depend on self"

to

  "cannot rebase change onto itself"

and add a test case for it.

Also fix a couple of minor nits in rebaseOntoAbandonedChange.

- use variable rather than calling getChangeId() again
- fix indentation

Change-Id: I70257c06af8872010958114537c092d4e9dcfc65

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/api/change/ChangeIT.java

@@ -477,11 +477,26 @@ public class ChangeIT extends AbstractDaemonTest {
     ri.base = r.getCommit().name();
 
     exception.expect(ResourceConflictException.class);
-    exception.expectMessage("base change is abandoned: " + r.getChangeId());
+    exception.expectMessage("base change is abandoned: " + changeId);
     gApi.changes()
-      .id(r2.getChangeId())
+        .id(r2.getChangeId())
-      .revision(r2.getCommit().name())
+        .revision(r2.getCommit().name())
-      .rebase(ri);
+        .rebase(ri);
+  }
+
+  @Test
+  public void rebaseOntoSelf() throws Exception {
+    PushOneCommit.Result r = createChange();
+    String changeId = r.getChangeId();
+    String commit = r.getCommit().name();
+    RebaseInput ri = new RebaseInput();
+    ri.base = commit;
+    exception.expect(ResourceConflictException.class);
+    exception.expectMessage("cannot rebase change onto itself");
+    gApi.changes()
+        .id(changeId)
+        .revision(commit)
+        .rebase(ri);
   }
 
   @Test

gerrit-server/src/main/java/com/google/gerrit/server/change/Rebase.java

@@ -152,7 +152,7 @@ public class Rebase implements RestModifyView<RevisionResource, RebaseInput>,
     if (!base.control().isPatchVisible(base.patchSet(), db)) {
       throw new AuthException("base revision not accessible: " + str);
     } else if (change.getId().equals(baseId.getParentKey())) {
-      throw new ResourceConflictException("cannot depend on self");
+      throw new ResourceConflictException("cannot rebase change onto itself");
     }
 
     Change baseChange = base.control().getChange();