presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/UnaliasSymbolReferences/visitProject
class UnaliasSymbolReferences:        @Override
        public PlanNode visitProject(ProjectNode node, RewriteContext<Void> context)
        {
            PlanNode source = context.rewrite(node.getSource());
            return new ProjectNode(node.getId(), source, canonicalize(node.getAssignments()));
        }