@Override
  public void update(@NotNull AnActionEvent e) {
    e.getPresentation().setText(VcsBundle.messagePointer("action.name.compare"));
    e.getPresentation().setDescription(VcsBundle.messagePointer("action.description.compare"));

    VcsFileRevision[] revisions = e.getData(VcsDataKeys.VCS_FILE_REVISIONS);
    VcsHistorySession historySession = e.getData(VcsDataKeys.HISTORY_SESSION);
    FilePath filePath = e.getData(VcsDataKeys.FILE_PATH);
    VcsHistoryProvider provider = e.getData(VcsDataKeys.HISTORY_PROVIDER);

    boolean isEnabled;
    if (revisions == null || historySession == null || filePath == null || provider == null) {
      isEnabled = false;
    }
    else if (revisions.length == 1) {
      isEnabled = historySession.isContentAvailable(revisions[0]) &&
                  e.getData(FileHistoryPanelImpl.PREVIOUS_REVISION_FOR_DIFF) != null;
    }
    else if (revisions.length == 2) {
      isEnabled = historySession.isContentAvailable(revisions[0]) &&
                  historySession.isContentAvailable(revisions[revisions.length - 1]);
    }
    else {
      isEnabled = false;
    }

    e.getPresentation().setEnabled(isEnabled);
  }
@Override
  public void update(@NotNull AnActionEvent e)