regenerator-transform/lib/emit.js

"use strict";

var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");
var _assert = _interopRequireDefault(require("assert"));
var leap = _interopRequireWildcard(require("./leap"));
var meta = _interopRequireWildcard(require("./meta"));
var util = _interopRequireWildcard(require("./util"));
function _getRequireWildcardCache(nodeInterop) { if (typeof WeakMap !== "function") return null; var cacheBabelInterop = new WeakMap(); var cacheNodeInterop = new WeakMap(); return (_getRequireWildcardCache = function _getRequireWildcardCache(nodeInterop) { return nodeInterop ? cacheNodeInterop : cacheBabelInterop; })(nodeInterop); }
function _interopRequireWildcard(obj, nodeInterop) { if (!nodeInterop && obj && obj.__esModule) { return obj; } if (obj === null || typeof obj !== "object" && typeof obj !== "function") { return { "default": obj }; } var cache = _getRequireWildcardCache(nodeInterop); if (cache && cache.has(obj)) { return cache.get(obj); } var newObj = {}; var hasPropertyDescriptor = Object.defineProperty && Object.getOwnPropertyDescriptor; for (var key in obj) { if (key !== "default" && Object.prototype.hasOwnProperty.call(obj, key)) { var desc = hasPropertyDescriptor ? Object.getOwnPropertyDescriptor(obj, key) : null; if (desc && (desc.get || desc.set)) { Object.defineProperty(newObj, key, desc); } else { newObj[key] = obj[key]; } } } newObj["default"] = obj; if (cache) { cache.set(obj, newObj); } return newObj; }
/**
 * Copyright (c) 2014-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

var hasOwn = Object.prototype.hasOwnProperty;
function Emitter(contextId) {
  _assert["default"].ok(this instanceof Emitter);
  util.getTypes().assertIdentifier(contextId);

  // Used to generate unique temporary names.
  this.nextTempId = 0;

  // In order to make sure the context object does not collide with
  // anything in the local scope, we might have to rename it, so we
  // refer to it symbolically instead of just assuming that it will be
  // called "context".
  this.contextId = contextId;

  // An append-only list of Statements that grows each time this.emit is
  // called.
  this.listing = [];

  // A sparse array whose keys correspond to locations in this.listing
  // that have been marked as branch/jump targets.
  this.marked = [true];
  this.insertedLocs = new Set();

  // The last location will be marked when this.getDispatchLoop is
  // called.
  this.finalLoc = this.loc();

  // A list of all leap.TryEntry statements emitted.
  this.tryEntries = [];

  // Each time we evaluate the body of a loop, we tell this.leapManager
  // to enter a nested loop context that determines the meaning of break
  // and continue statements therein.
  this.leapManager = new leap.LeapManager(this);
}
var Ep = Emitter.prototype;
exports.Emitter = Emitter;

// Offsets into this.listing that could be used as targets for branches or
// jumps are represented as numeric Literal nodes. This representation has
// the amazingly convenient benefit of allowing the exact value of the
// location to be determined at any time, even after generating code that
// refers to the location.
// We use 'Number.MAX_VALUE' to mark uninitialized location. We can safely do
// so because no code can realistically have about 1.8e+308 locations before
// hitting memory limit of the machine it's running on. For comparison, the
// estimated number of atoms in the observable universe is around 1e+80.
var PENDING_LOCATION = Number.MAX_VALUE;
Ep.loc = function () {
  var l = util.getTypes().numericLiteral(PENDING_LOCATION);
  this.insertedLocs.add(l);
  return l;
};
Ep.getInsertedLocs = function () {
  return this.insertedLocs;
};
Ep.getContextId = function () {
  return util.getTypes().clone(this.contextId);
};

// Sets the exact value of the given location to the offset of the next
// Statement emitted.
Ep.mark = function (loc) {
  util.getTypes().assertLiteral(loc);
  var index = this.listing.length;
  if (loc.value === PENDING_LOCATION) {
    loc.value = index;
  } else {
    // Locations can be marked redundantly, but their values cannot change
    // once set the first time.
    _assert["default"].strictEqual(loc.value, index);
  }
  this.marked[index] = true;
  return loc;
};
Ep.emit = function (node) {
  var t = util.getTypes();
  if (t.isExpression(node)) {
    node = t.expressionStatement(node);
  }
  t.assertStatement(node);
  this.listing.push(node);
};

// Shorthand for emitting assignment statements. This will come in handy
// for assignments to temporary variables.
Ep.emitAssign = function (lhs, rhs) {
  this.emit(this.assign(lhs, rhs));
  return lhs;
};

// Shorthand for an assignment statement.
Ep.assign = function (lhs, rhs) {
  var t = util.getTypes();
  return t.expressionStatement(t.assignmentExpression("=", t.cloneDeep(lhs), rhs));
};

// Convenience function for generating expressions like context.next,
// context.sent, and context.rval.
Ep.contextProperty = function (name, computed) {
  var t = util.getTypes();
  return t.memberExpression(this.getContextId(), computed ? t.stringLiteral(name) : t.identifier(name), !!computed);
};

// Shorthand for setting context.rval and jumping to `context.stop()`.
Ep.stop = function (rval) {
  if (rval) {
    this.setReturnValue(rval);
  }
  this.jump(this.finalLoc);
};
Ep.setReturnValue = function (valuePath) {
  util.getTypes().assertExpression(valuePath.value);
  this.emitAssign(this.contextProperty("rval"), this.explodeExpression(valuePath));
};
Ep.clearPendingException = function (tryLoc, assignee) {
  var t = util.getTypes();
  t.assertLiteral(tryLoc);
  var catchCall = t.callExpression(this.contextProperty("catch", true), [t.clone(tryLoc)]);
  if (assignee) {
    this.emitAssign(assignee, catchCall);
  } else {
    this.emit(catchCall);
  }
};

// Emits code for an unconditional jump to the given location, even if the
// exact value of the location is not yet known.
Ep.jump = function (toLoc) {
  this.emitAssign(this.contextProperty("next"), toLoc);
  this.emit(util.getTypes().breakStatement());
};

// Conditional jump.
Ep.jumpIf = function (test, toLoc) {
  var t = util.getTypes();
  t.assertExpression(test);
  t.assertLiteral(toLoc);
  this.emit(t.ifStatement(test, t.blockStatement([this.assign(this.contextProperty("next"), toLoc), t.breakStatement()])));
};

// Conditional jump, with the condition negated.
Ep.jumpIfNot = function (test, toLoc) {
  var t = util.getTypes();
  t.assertExpression(test);
  t.assertLiteral(toLoc);
  var negatedTest;
  if (t.isUnaryExpression(test) && test.operator === "!") {
    // Avoid double negation.
    negatedTest = test.argument;
  } else {
    negatedTest = t.unaryExpression("!", test);
  }
  this.emit(t.ifStatement(negatedTest, t.blockStatement([this.assign(this.contextProperty("next"), toLoc), t.breakStatement()])));
};

// Returns a unique MemberExpression that can be used to store and
// retrieve temporary values. Since the object of the member expression is
// the context object, which is presumed to coexist peacefully with all
// other local variables, and since we just increment `nextTempId`
// monotonically, uniqueness is assured.
Ep.makeTempVar = function () {
  return this.contextProperty("t" + this.nextTempId++);
};
Ep.getContextFunction = function (id) {
  var t = util.getTypes();
  return t.functionExpression(id || null /*Anonymous*/, [this.getContextId()], t.blockStatement([this.getDispatchLoop()]), false,
  // Not a generator anymore!
  false // Nor an expression.
  );
};

// Turns this.listing into a loop of the form
//
//   while (1) switch (context.next) {
//   case 0:
//   ...
//   case n:
//     return context.stop();
//   }
//
// Each marked location in this.listing will correspond to one generated
// case statement.
Ep.getDispatchLoop = function () {
  var self = this;
  var t = util.getTypes();
  var cases = [];
  var current;

  // If we encounter a break, continue, or return statement in a switch
  // case, we can skip the rest of the statements until the next case.
  var alreadyEnded = false;
  self.listing.forEach(function (stmt, i) {
    if (self.marked.hasOwnProperty(i)) {
      cases.push(t.switchCase(t.numericLiteral(i), current = []));
      alreadyEnded = false;
    }
    if (!alreadyEnded) {
      current.push(stmt);
      if (t.isCompletionStatement(stmt)) alreadyEnded = true;
    }
  });

  // Now that we know how many statements there will be in this.listing,
  // we can finally resolve this.finalLoc.value.
  this.finalLoc.value = this.listing.length;
  cases.push(t.switchCase(this.finalLoc, [
    // Intentionally fall through to the "end" case...
  ]),
  // So that the runtime can jump to the final location without having
  // to know its offset, we provide the "end" case as a synonym.
  t.switchCase(t.stringLiteral("end"), [
  // This will check/clear both context.thrown and context.rval.
  t.returnStatement(t.callExpression(this.contextProperty("stop"), []))]));
  return t.whileStatement(t.numericLiteral(1), t.switchStatement(t.assignmentExpression("=", this.contextProperty("prev"), this.contextProperty("next")), cases));
};
Ep.getTryLocsList = function () {
  if (this.tryEntries.length === 0) {
    // To avoid adding a needless [] to the majority of runtime.wrap
    // argument lists, force the caller to handle this case specially.
    return null;
  }
  var t = util.getTypes();
  var lastLocValue = 0;
  return t.arrayExpression(this.tryEntries.map(function (tryEntry) {
    var thisLocValue = tryEntry.firstLoc.value;
    _assert["default"].ok(thisLocValue >= lastLocValue, "try entries out of order");
    lastLocValue = thisLocValue;
    var ce = tryEntry.catchEntry;
    var fe = tryEntry.finallyEntry;
    var locs = [tryEntry.firstLoc,
    // The null here makes a hole in the array.
    ce ? ce.firstLoc : null];
    if (fe) {
      locs[2] = fe.firstLoc;
      locs[3] = fe.afterLoc;
    }
    return t.arrayExpression(locs.map(function (loc) {
      return loc && t.clone(loc);
    }));
  }));
};

// All side effects must be realized in order.

// If any subexpression harbors a leap, all subexpressions must be
// neutered of side effects.

// No destructive modification of AST nodes.

Ep.explode = function (path, ignoreResult) {
  var t = util.getTypes();
  var node = path.node;
  var self = this;
  t.assertNode(node);
  if (t.isDeclaration(node)) throw getDeclError(node);
  if (t.isStatement(node)) return self.explodeStatement(path);
  if (t.isExpression(node)) return self.explodeExpression(path, ignoreResult);
  switch (node.type) {
    case "Program":
      return path.get("body").map(self.explodeStatement, self);
    case "VariableDeclarator":
      throw getDeclError(node);

    // These node types should be handled by their parent nodes
    // (ObjectExpression, SwitchStatement, and TryStatement, respectively).
    case "Property":
    case "SwitchCase":
    case "CatchClause":
      throw new Error(node.type + " nodes should be handled by their parents");
    default:
      throw new Error("unknown Node of type " + JSON.stringify(node.type));
  }
};
function getDeclError(node) {
  return new Error("all declarations should have been transformed into " + "assignments before the Exploder began its work: " + JSON.stringify(node));
}
Ep.explodeStatement = function (path, labelId) {
  var t = util.getTypes();
  var stmt = path.node;
  var self = this;
  var before, after, head;
  t.assertStatement(stmt);
  if (labelId) {
    t.assertIdentifier(labelId);
  } else {
    labelId = null;
  }

  // Explode BlockStatement nodes even if they do not contain a yield,
  // because we don't want or need the curly braces.
  if (t.isBlockStatement(stmt)) {
    path.get("body").forEach(function (path) {
      self.explodeStatement(path);
    });
    return;
  }
  if (!meta.containsLeap(stmt)) {
    // Technically we should be able to avoid emitting the statement
    // altogether if !meta.hasSideEffects(stmt), but that leads to
    // confusing generated code (for instance, `while (true) {}` just
    // disappears) and is probably a more appropriate job for a dedicated
    // dead code elimination pass.
    self.emit(stmt);
    return;
  }
  switch (stmt.type) {
    case "ExpressionStatement":
      self.explodeExpression(path.get("expression"), true);
      break;
    case "LabeledStatement":
      after = this.loc();

      // Did you know you can break from any labeled block statement or
      // control structure? Well, you can! Note: when a labeled loop is
      // encountered, the leap.LabeledEntry created here will immediately
      // enclose a leap.LoopEntry on the leap manager's stack, and both
      // entries will have the same label. Though this works just fine, it
      // may seem a bit redundant. In theory, we could check here to
      // determine if stmt knows how to handle its own label; for example,
      // stmt happens to be a WhileStatement and so we know it's going to
      // establish its own LoopEntry when we explode it (below). Then this
      // LabeledEntry would be unnecessary. Alternatively, we might be
      // tempted not to pass stmt.label down into self.explodeStatement,
      // because we've handled the label here, but that's a mistake because
      // labeled loops may contain labeled continue statements, which is not
      // something we can handle in this generic case. All in all, I think a
      // little redundancy greatly simplifies the logic of this case, since
      // it's clear that we handle all possible LabeledStatements correctly
      // here, regardless of whether they interact with the leap manager
      // themselves. Also remember that labels and break/continue-to-label
      // statements are rare, and all of this logic happens at transform
      // time, so it has no additional runtime cost.
      self.leapManager.withEntry(new leap.LabeledEntry(after, stmt.label), function () {
        self.explodeStatement(path.get("body"), stmt.label);
      });
      self.mark(after);
      break;
    case "WhileStatement":
      before = this.loc();
      after = this.loc();
      self.mark(before);
      self.jumpIfNot(self.explodeExpression(path.get("test")), after);
      self.leapManager.withEntry(new leap.LoopEntry(after, before, labelId), function () {
        self.explodeStatement(path.get("body"));
      });
      self.jump(before);
      self.mark(after);
      break;
    case "DoWhileStatement":
      var first = this.loc();
      var test = this.loc();
      after = this.loc();
      self.mark(first);
      self.leapManager.withEntry(new leap.LoopEntry(after, test, labelId), function () {
        self.explode(path.get("body"));
      });
      self.mark(test);
      self.jumpIf(self.explodeExpression(path.get("test")), first);
      self.mark(after);
      break;
    case "ForStatement":
      head = this.loc();
      var update = this.loc();
      after = this.loc();
      if (stmt.init) {
        // We pass true here to indicate that if stmt.init is an expression
        // then we do not care about its result.
        self.explode(path.get("init"), true);
      }
      self.mark(head);
      if (stmt.test) {
        self.jumpIfNot(self.explodeExpression(path.get("test")), after);
      } else {
        // No test means continue unconditionally.
      }
      self.leapManager.withEntry(new leap.LoopEntry(after, update, labelId), function () {
        self.explodeStatement(path.get("body"));
      });
      self.mark(update);
      if (stmt.update) {
        // We pass true here to indicate that if stmt.update is an
        // expression then we do not care about its result.
        self.explode(path.get("update"), true);
      }
      self.jump(head);
      self.mark(after);
      break;
    case "TypeCastExpression":
      return self.explodeExpression(path.get("expression"));
    case "ForInStatement":
      head = this.loc();
      after = this.loc();
      var keyIterNextFn = self.makeTempVar();
      self.emitAssign(keyIterNextFn, t.callExpression(util.runtimeProperty("keys"), [self.explodeExpression(path.get("right"))]));
      self.mark(head);
      var keyInfoTmpVar = self.makeTempVar();
      self.jumpIf(t.memberExpression(t.assignmentExpression("=", keyInfoTmpVar, t.callExpression(t.cloneDeep(keyIterNextFn), [])), t.identifier("done"), false), after);
      self.emitAssign(stmt.left, t.memberExpression(t.cloneDeep(keyInfoTmpVar), t.identifier("value"), false));
      self.leapManager.withEntry(new leap.LoopEntry(after, head, labelId), function () {
        self.explodeStatement(path.get("body"));
      });
      self.jump(head);
      self.mark(after);
      break;
    case "BreakStatement":
      self.emitAbruptCompletion({
        type: "break",
        target: self.leapManager.getBreakLoc(stmt.label)
      });
      break;
    case "ContinueStatement":
      self.emitAbruptCompletion({
        type: "continue",
        target: self.leapManager.getContinueLoc(stmt.label)
      });
      break;
    case "SwitchStatement":
      // Always save the discriminant into a temporary variable in case the
      // test expressions overwrite values like context.sent.
      var disc = self.emitAssign(self.makeTempVar(), self.explodeExpression(path.get("discriminant")));
      after = this.loc();
      var defaultLoc = this.loc();
      var condition = defaultLoc;
      var caseLocs = [];

      // If there are no cases, .cases might be undefined.
      var cases = stmt.cases || [];
      for (var i = cases.length - 1; i >= 0; --i) {
        var c = cases[i];
        t.assertSwitchCase(c);
        if (c.test) {
          condition = t.conditionalExpression(t.binaryExpression("===", t.cloneDeep(disc), c.test), caseLocs[i] = this.loc(), condition);
        } else {
          caseLocs[i] = defaultLoc;
        }
      }
      var discriminant = path.get("discriminant");
      util.replaceWithOrRemove(discriminant, condition);
      self.jump(self.explodeExpression(discriminant));
      self.leapManager.withEntry(new leap.SwitchEntry(after), function () {
        path.get("cases").forEach(function (casePath) {
          var i = casePath.key;
          self.mark(caseLocs[i]);
          casePath.get("consequent").forEach(function (path) {
            self.explodeStatement(path);
          });
        });
      });
      self.mark(after);
      if (defaultLoc.value === PENDING_LOCATION) {
        self.mark(defaultLoc);
        _assert["default"].strictEqual(after.value, defaultLoc.value);
      }
      break;
    case "IfStatement":
      var elseLoc = stmt.alternate && this.loc();
      after = this.loc();
      self.jumpIfNot(self.explodeExpression(path.get("test")), elseLoc || after);
      self.explodeStatement(path.get("consequent"));
      if (elseLoc) {
        self.jump(after);
        self.mark(elseLoc);
        self.explodeStatement(path.get("alternate"));
      }
      self.mark(after);
      break;
    case "ReturnStatement":
      self.emitAbruptCompletion({
        type: "return",
        value: self.explodeExpression(path.get("argument"))
      });
      break;
    case "WithStatement":
      throw new Error("WithStatement not supported in generator functions.");
    case "TryStatement":
      after = this.loc();
      var handler = stmt.handler;
      var catchLoc = handler && this.loc();
      var catchEntry = catchLoc && new leap.CatchEntry(catchLoc, handler.param);
      var finallyLoc = stmt.finalizer && this.loc();
      var finallyEntry = finallyLoc && new leap.FinallyEntry(finallyLoc, after);
      var tryEntry = new leap.TryEntry(self.getUnmarkedCurrentLoc(), catchEntry, finallyEntry);
      self.tryEntries.push(tryEntry);
      self.updateContextPrevLoc(tryEntry.firstLoc);
      self.leapManager.withEntry(tryEntry, function () {
        self.explodeStatement(path.get("block"));
        if (catchLoc) {
          if (finallyLoc) {
            // If we have both a catch block and a finally block, then
            // because we emit the catch block first, we need to jump over
            // it to the finally block.
            self.jump(finallyLoc);
          } else {
            // If there is no finally block, then we need to jump over the
            // catch block to the fall-through location.
            self.jump(after);
          }
          self.updateContextPrevLoc(self.mark(catchLoc));
          var bodyPath = path.get("handler.body");
          var safeParam = self.makeTempVar();
          self.clearPendingException(tryEntry.firstLoc, safeParam);
          bodyPath.traverse(catchParamVisitor, {
            getSafeParam: function getSafeParam() {
              return t.cloneDeep(safeParam);
            },
            catchParamName: handler.param.name
          });
          self.leapManager.withEntry(catchEntry, function () {
            self.explodeStatement(bodyPath);
          });
        }
        if (finallyLoc) {
          self.updateContextPrevLoc(self.mark(finallyLoc));
          self.leapManager.withEntry(finallyEntry, function () {
            self.explodeStatement(path.get("finalizer"));
          });
          self.emit(t.returnStatement(t.callExpression(self.contextProperty("finish"), [finallyEntry.firstLoc])));
        }
      });
      self.mark(after);
      break;
    case "ThrowStatement":
      self.emit(t.throwStatement(self.explodeExpression(path.get("argument"))));
      break;
    case "ClassDeclaration":
      self.emit(self.explodeClass(path));
      break;
    default:
      throw new Error("unknown Statement of type " + JSON.stringify(stmt.type));
  }
};
var catchParamVisitor = {
  Identifier: function Identifier(path, state) {
    if (path.node.name === state.catchParamName && util.isReference(path)) {
      util.replaceWithOrRemove(path, state.getSafeParam());
    }
  },
  Scope: function Scope(path, state) {
    if (path.scope.hasOwnBinding(state.catchParamName)) {
      // Don't descend into nested scopes that shadow the catch
      // parameter with their own declarations.
      path.skip();
    }
  }
};
Ep.emitAbruptCompletion = function (record) {
  if (!isValidCompletion(record)) {
    _assert["default"].ok(false, "invalid completion record: " + JSON.stringify(record));
  }
  _assert["default"].notStrictEqual(record.type, "normal", "normal completions are not abrupt");
  var t = util.getTypes();
  var abruptArgs = [t.stringLiteral(record.type)];
  if (record.type === "break" || record.type === "continue") {
    t.assertLiteral(record.target);
    abruptArgs[1] = this.insertedLocs.has(record.target) ? record.target : t.cloneDeep(record.target);
  } else if (record.type === "return" || record.type === "throw") {
    if (record.value) {
      t.assertExpression(record.value);
      abruptArgs[1] = this.insertedLocs.has(record.value) ? record.value : t.cloneDeep(record.value);
    }
  }
  this.emit(t.returnStatement(t.callExpression(this.contextProperty("abrupt"), abruptArgs)));
};
function isValidCompletion(record) {
  var type = record.type;
  if (type === "normal") {
    return !hasOwn.call(record, "target");
  }
  if (type === "break" || type === "continue") {
    return !hasOwn.call(record, "value") && util.getTypes().isLiteral(record.target);
  }
  if (type === "return" || type === "throw") {
    return hasOwn.call(record, "value") && !hasOwn.call(record, "target");
  }
  return false;
}

// Not all offsets into emitter.listing are potential jump targets. For
// example, execution typically falls into the beginning of a try block
// without jumping directly there. This method returns the current offset
// without marking it, so that a switch case will not necessarily be
// generated for this offset (I say "not necessarily" because the same
// location might end up being marked in the process of emitting other
// statements). There's no logical harm in marking such locations as jump
// targets, but minimizing the number of switch cases keeps the generated
// code shorter.
Ep.getUnmarkedCurrentLoc = function () {
  return util.getTypes().numericLiteral(this.listing.length);
};

// The context.prev property takes the value of context.next whenever we
// evaluate the switch statement discriminant, which is generally good
// enough for tracking the last location we jumped to, but sometimes
// context.prev needs to be more precise, such as when we fall
// successfully out of a try block and into a finally block without
// jumping. This method exists to update context.prev to the freshest
// available location. If we were implementing a full interpreter, we
// would know the location of the current instruction with complete
// precision at all times, but we don't have that luxury here, as it would
// be costly and verbose to set context.prev before every statement.
Ep.updateContextPrevLoc = function (loc) {
  var t = util.getTypes();
  if (loc) {
    t.assertLiteral(loc);
    if (loc.value === PENDING_LOCATION) {
      // If an uninitialized location literal was passed in, set its value
      // to the current this.listing.length.
      loc.value = this.listing.length;
    } else {
      // Otherwise assert that the location matches the current offset.
      _assert["default"].strictEqual(loc.value, this.listing.length);
    }
  } else {
    loc = this.getUnmarkedCurrentLoc();
  }

  // Make sure context.prev is up to date in case we fell into this try
  // statement without jumping to it. TODO Consider avoiding this
  // assignment when we know control must have jumped here.
  this.emitAssign(this.contextProperty("prev"), loc);
};

// In order to save the rest of explodeExpression from a combinatorial
// trainwreck of special cases, explodeViaTempVar is responsible for
// deciding when a subexpression needs to be "exploded," which is my
// very technical term for emitting the subexpression as an assignment
// to a temporary variable and the substituting the temporary variable
// for the original subexpression. Think of exploded view diagrams, not
// Michael Bay movies. The point of exploding subexpressions is to
// control the precise order in which the generated code realizes the
// side effects of those subexpressions.
Ep.explodeViaTempVar = function (tempVar, childPath, hasLeapingChildren, ignoreChildResult) {
  _assert["default"].ok(!ignoreChildResult || !tempVar, "Ignoring the result of a child expression but forcing it to " + "be assigned to a temporary variable?");
  var t = util.getTypes();
  var result = this.explodeExpression(childPath, ignoreChildResult);
  if (ignoreChildResult) {
    // Side effects already emitted above.
  } else if (tempVar || hasLeapingChildren && !t.isLiteral(result)) {
    // If tempVar was provided, then the result will always be assigned
    // to it, even if the result does not otherwise need to be assigned
    // to a temporary variable.  When no tempVar is provided, we have
    // the flexibility to decide whether a temporary variable is really
    // necessary.  Unfortunately, in general, a temporary variable is
    // required whenever any child contains a yield expression, since it
    // is difficult to prove (at all, let alone efficiently) whether
    // this result would evaluate to the same value before and after the
    // yield (see #206).  One narrow case where we can prove it doesn't
    // matter (and thus we do not need a temporary variable) is when the
    // result in question is a Literal value.
    result = this.emitAssign(tempVar || this.makeTempVar(), result);
  }
  return result;
};
Ep.explodeExpression = function (path, ignoreResult) {
  var t = util.getTypes();
  var expr = path.node;
  if (expr) {
    t.assertExpression(expr);
  } else {
    return expr;
  }
  var self = this;
  var result; // Used optionally by several cases below.
  var after;
  function finish(expr) {
    t.assertExpression(expr);
    if (ignoreResult) {
      self.emit(expr);
    }
    return expr;
  }

  // If the expression does not contain a leap, then we either emit the
  // expression as a standalone statement or return it whole.
  if (!meta.containsLeap(expr)) {
    return finish(expr);
  }

  // If any child contains a leap (such as a yield or labeled continue or
  // break statement), then any sibling subexpressions will almost
  // certainly have to be exploded in order to maintain the order of their
  // side effects relative to the leaping child(ren).
  var hasLeapingChildren = meta.containsLeap.onlyChildren(expr);

  // If ignoreResult is true, then we must take full responsibility for
  // emitting the expression with all its side effects, and we should not
  // return a result.

  switch (expr.type) {
    case "MemberExpression":
      return finish(t.memberExpression(self.explodeExpression(path.get("object")), expr.computed ? self.explodeViaTempVar(null, path.get("property"), hasLeapingChildren) : expr.property, expr.computed));
    case "CallExpression":
      var calleePath = path.get("callee");
      var argsPath = path.get("arguments");
      var newCallee;
      var newArgs;
      var hasLeapingArgs = argsPath.some(function (argPath) {
        return meta.containsLeap(argPath.node);
      });
      var injectFirstArg = null;
      if (t.isMemberExpression(calleePath.node)) {
        if (hasLeapingArgs) {
          // If the arguments of the CallExpression contained any yield
          // expressions, then we need to be sure to evaluate the callee
          // before evaluating the arguments, but if the callee was a member
          // expression, then we must be careful that the object of the
          // member expression still gets bound to `this` for the call.

          var newObject = self.explodeViaTempVar(
          // Assign the exploded callee.object expression to a temporary
          // variable so that we can use it twice without reevaluating it.
          self.makeTempVar(), calleePath.get("object"), hasLeapingChildren);
          var newProperty = calleePath.node.computed ? self.explodeViaTempVar(null, calleePath.get("property"), hasLeapingChildren) : calleePath.node.property;
          injectFirstArg = newObject;
          newCallee = t.memberExpression(t.memberExpression(t.cloneDeep(newObject), newProperty, calleePath.node.computed), t.identifier("call"), false);
        } else {
          newCallee = self.explodeExpression(calleePath);
        }
      } else {
        newCallee = self.explodeViaTempVar(null, calleePath, hasLeapingChildren);
        if (t.isMemberExpression(newCallee)) {
          // If the callee was not previously a MemberExpression, then the
          // CallExpression was "unqualified," meaning its `this` object
          // should be the global object. If the exploded expression has
          // become a MemberExpression (e.g. a context property, probably a
          // temporary variable), then we need to force it to be unqualified
          // by using the (0, object.property)(...) trick; otherwise, it
          // will receive the object of the MemberExpression as its `this`
          // object.
          newCallee = t.sequenceExpression([t.numericLiteral(0), t.cloneDeep(newCallee)]);
        }
      }
      if (hasLeapingArgs) {
        newArgs = argsPath.map(function (argPath) {
          return self.explodeViaTempVar(null, argPath, hasLeapingChildren);
        });
        if (injectFirstArg) newArgs.unshift(injectFirstArg);
        newArgs = newArgs.map(function (arg) {
          return t.cloneDeep(arg);
        });
      } else {
        newArgs = path.node.arguments;
      }
      return finish(t.callExpression(newCallee, newArgs));
    case "NewExpression":
      return finish(t.newExpression(self.explodeViaTempVar(null, path.get("callee"), hasLeapingChildren), path.get("arguments").map(function (argPath) {
        return self.explodeViaTempVar(null, argPath, hasLeapingChildren);
      })));
    case "ObjectExpression":
      return finish(t.objectExpression(path.get("properties").map(function (propPath) {
        if (propPath.isObjectProperty()) {
          return t.objectProperty(propPath.node.key, self.explodeViaTempVar(null, propPath.get("value"), hasLeapingChildren), propPath.node.computed);
        } else {
          return propPath.node;
        }
      })));
    case "ArrayExpression":
      return finish(t.arrayExpression(path.get("elements").map(function (elemPath) {
        if (!elemPath.node) {
          return null;
        }
        if (elemPath.isSpreadElement()) {
          return t.spreadElement(self.explodeViaTempVar(null, elemPath.get("argument"), hasLeapingChildren));
        } else {
          return self.explodeViaTempVar(null, elemPath, hasLeapingChildren);
        }
      })));
    case "SequenceExpression":
      var lastIndex = expr.expressions.length - 1;
      path.get("expressions").forEach(function (exprPath) {
        if (exprPath.key === lastIndex) {
          result = self.explodeExpression(exprPath, ignoreResult);
        } else {
          self.explodeExpression(exprPath, true);
        }
      });
      return result;
    case "LogicalExpression":
      after = this.loc();
      if (!ignoreResult) {
        result = self.makeTempVar();
      }
      var left = self.explodeViaTempVar(result, path.get("left"), hasLeapingChildren);
      if (expr.operator === "&&") {
        self.jumpIfNot(left, after);
      } else {
        _assert["default"].strictEqual(expr.operator, "||");
        self.jumpIf(left, after);
      }
      self.explodeViaTempVar(result, path.get("right"), hasLeapingChildren, ignoreResult);
      self.mark(after);
      return result;
    case "ConditionalExpression":
      var elseLoc = this.loc();
      after = this.loc();
      var test = self.explodeExpression(path.get("test"));
      self.jumpIfNot(test, elseLoc);
      if (!ignoreResult) {
        result = self.makeTempVar();
      }
      self.explodeViaTempVar(result, path.get("consequent"), hasLeapingChildren, ignoreResult);
      self.jump(after);
      self.mark(elseLoc);
      self.explodeViaTempVar(result, path.get("alternate"), hasLeapingChildren, ignoreResult);
      self.mark(after);
      return result;
    case "UnaryExpression":
      return finish(t.unaryExpression(expr.operator,
      // Can't (and don't need to) break up the syntax of the argument.
      // Think about delete a[b].
      self.explodeExpression(path.get("argument")), !!expr.prefix));
    case "BinaryExpression":
      return finish(t.binaryExpression(expr.operator, self.explodeViaTempVar(null, path.get("left"), hasLeapingChildren), self.explodeViaTempVar(null, path.get("right"), hasLeapingChildren)));
    case "AssignmentExpression":
      if (expr.operator === "=") {
        // If this is a simple assignment, the left hand side does not need
        // to be read before the right hand side is evaluated, so we can
        // avoid the more complicated logic below.
        return finish(t.assignmentExpression(expr.operator, self.explodeExpression(path.get("left")), self.explodeExpression(path.get("right"))));
      }
      var lhs = self.explodeExpression(path.get("left"));
      var temp = self.emitAssign(self.makeTempVar(), lhs);

      // For example,
      //
      //   x += yield y
      //
      // becomes
      //
      //   context.t0 = x
      //   x = context.t0 += yield y
      //
      // so that the left-hand side expression is read before the yield.
      // Fixes https://github.com/facebook/regenerator/issues/345.

      return finish(t.assignmentExpression("=", t.cloneDeep(lhs), t.assignmentExpression(expr.operator, t.cloneDeep(temp), self.explodeExpression(path.get("right")))));
    case "UpdateExpression":
      return finish(t.updateExpression(expr.operator, self.explodeExpression(path.get("argument")), expr.prefix));
    case "YieldExpression":
      after = this.loc();
      var arg = expr.argument && self.explodeExpression(path.get("argument"));
      if (arg && expr.delegate) {
        var _result = self.makeTempVar();
        var _ret = t.returnStatement(t.callExpression(self.contextProperty("delegateYield"), [arg, t.stringLiteral(_result.property.name), after]));
        _ret.loc = expr.loc;
        self.emit(_ret);
        self.mark(after);
        return _result;
      }
      self.emitAssign(self.contextProperty("next"), after);
      var ret = t.returnStatement(t.cloneDeep(arg) || null);
      // Preserve the `yield` location so that source mappings for the statements
      // link back to the yield properly.
      ret.loc = expr.loc;
      self.emit(ret);
      self.mark(after);
      return self.contextProperty("sent");
    case "ClassExpression":
      return finish(self.explodeClass(path));
    default:
      throw new Error("unknown Expression of type " + JSON.stringify(expr.type));
  }
};
Ep.explodeClass = function (path) {
  var explodingChildren = [];
  if (path.node.superClass) {
    explodingChildren.push(path.get("superClass"));
  }
  path.get("body.body").forEach(function (member) {
    if (member.node.computed) {
      explodingChildren.push(member.get("key"));
    }
  });
  var hasLeapingChildren = explodingChildren.some(function (child) {
    return meta.containsLeap(child);
  });
  for (var i = 0; i < explodingChildren.length; i++) {
    var child = explodingChildren[i];
    var isLast = i === explodingChildren.length - 1;
    if (isLast) {
      child.replaceWith(this.explodeExpression(child));
    } else {
      child.replaceWith(this.explodeViaTempVar(null, child, hasLeapingChildren));
    }
  }
  return path.node;
};