ali.regenerator/lib/meta.js

Source transformer enabling ECMAScript 6 generator functions (yield) in JavaScript-of-today (ES5)

/**
 * Copyright (c) 2014, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
 * additional grant of patent rights can be found in the PATENTS file in
 * the same directory.
 */

var assert = require("assert");
var m = require("private").makeAccessor();
var types = require("recast-harmony").types;
var isArray = types.builtInTypes.array;
var n = types.namedTypes;
var hasOwn = Object.prototype.hasOwnProperty;

function makePredicate(propertyName, knownTypes) {
  function onlyChildren(node) {
    n.Node.assert(node);

    // Assume no side effects until we find out otherwise.
    var result = false;

    function check(child) {
      if (result) {
        // Do nothing.
      } else if (isArray.check(child)) {
        child.some(check);
      } else if (n.Node.check(child)) {
        assert.strictEqual(result, false);
        result = predicate(child);
      }
      return result;
    }

    types.eachField(node, function(name, child) {
      check(child);
    });

    return result;
  }

  function predicate(node) {
    n.Node.assert(node);

    var meta = m(node);
    if (hasOwn.call(meta, propertyName))
      return meta[propertyName];

    // Certain types are "opaque," which means they have no side
    // effects or leaps and we don't care about their subexpressions.
    if (hasOwn.call(opaqueTypes, node.type))
      return meta[propertyName] = false;

    if (hasOwn.call(knownTypes, node.type))
      return meta[propertyName] = true;

    return meta[propertyName] = onlyChildren(node);
  }

  predicate.onlyChildren = onlyChildren;

  return predicate;
}

var opaqueTypes = {
  FunctionExpression: true
};

// These types potentially have side effects regardless of what side
// effects their subexpressions have.
var sideEffectTypes = {
  CallExpression: true, // Anything could happen!
  ForInStatement: true, // Modifies the key variable.
  UnaryExpression: true, // Think delete.
  BinaryExpression: true, // Might invoke .toString() or .valueOf().
  AssignmentExpression: true, // Side-effecting by definition.
  UpdateExpression: true, // Updates are essentially assignments.
  NewExpression: true // Similar to CallExpression.
};

// These types are the direct cause of all leaps in control flow.
var leapTypes = {
  YieldExpression: true,
  BreakStatement: true,
  ContinueStatement: true,
  ReturnStatement: true,
  ThrowStatement: true
};

// All leap types are also side effect types.
for (var type in leapTypes) {
  if (hasOwn.call(leapTypes, type)) {
    sideEffectTypes[type] = leapTypes[type];
  }
}

exports.hasSideEffects = makePredicate("hasSideEffects", sideEffectTypes);
exports.containsLeap = makePredicate("containsLeap", leapTypes);