code: func (g *Cloud) ListInstanceGroups(zone string) ([]*compute.InstanceGroup, error) {
  	ctx, cancel := cloud.ContextWithCallTimeout()
  	defer cancel()
  
  	mc := newInstanceGroupMetricContext("list", zone)
  	v, err := g.c.InstanceGroups().List(ctx, zone, filter.None)
  	return v, mc.Observe(err)
  }
docs: // ListInstanceGroups lists all InstanceGroups in the project and
  // zone.