pegjs/lib/compiler/passes/remove-proxy-rules.js

"use strict";

let visitor = require("../visitor");

/*
 * Removes proxy rules -- that is, rules that only delegate to other rule.
 */
function removeProxyRules(ast, options) {
  function isProxyRule(node) {
    return node.type === "rule" && node.expression.type === "rule_ref";
  }

  function replaceRuleRefs(ast, from, to) {
    let replace = visitor.build({
      rule_ref: function(node) {
        if (node.name === from) {
          node.name = to;
        }
      }
    });

    replace(ast);
  }

  let indices = [];

  ast.rules.forEach((rule, i) => {
    if (isProxyRule(rule)) {
      replaceRuleRefs(ast, rule.name, rule.expression.name);
      if (options.allowedStartRules.indexOf(rule.name) === -1) {
        indices.push(i);
      }
    }
  });

  indices.reverse();

  indices.forEach(i => { ast.rules.splice(i, 1); });
}

module.exports = removeProxyRules;