@Override
  public BuildResult call() throws IOException, RegistryException {
    EventHandlers eventHandlers = buildContext.getEventHandlers();
    try (TimerEventDispatcher ignored = new TimerEventDispatcher(eventHandlers, DESCRIPTION);
        ProgressEventDispatcher ignored2 =
            progressEventDispatcherFactory.create("pushing manifest for " + imageQualifier, 1)) {
      eventHandlers.dispatch(LogEvent.info("Pushing manifest for " + imageQualifier + "..."));

      registryClient.pushManifest(manifestTemplate, imageQualifier);
      return new BuildResult(imageDigest, imageId, true);
    }
  }
Pushes a manifest or a manifest list for a tag. If not a manifest list, returns the manifest
digest ("image digest") and the container configuration digest ("image id") as {@link
BuildResult}. If a manifest list, returns the manifest list digest only.
jib-core/src/main/java/com/google/cloud/tools/jib/builder/steps/PushImageStep.java