code: func (g *oneofGroup) onAlternativePicked(alt *oneofAlternative, dict starlark.StringDict) {
  	for _, a := range g.alternatives {
  		if a != alt {
  			delete(dict, a.name)
  		}
  	}
  }
docs: // onAlternativePicked is called when one oneof alternative was set to.
  //
  // It clears all others.