optimized-out-arrow-this.js

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var g = newGlobal({newCompartment: true});

var dbg = new Debugger(g);

g.eval(`

function f() {

  // |this| in arrow-functions refers to the |this| binding in outer functions.

  // So when |frame.eval("this")| is executed, the outer |this| binding should

  // be returned, unless it has been optimised out.

  (() => {})();

  // Ensure a |this| binding is created for |f|.

  return this;

`);

var errors = [];

function enterFrame(frame) {

  // Disable the handler so we don't call it recursively through |frame.eval|.

  dbg.onEnterFrame = undefined;

  // Store the error when resolving |this| was unsuccessful.

  var r = frame.eval("this");

  if (r.throw) {

    errors.push(r.throw);

  // Re-enable the handler.

  dbg.onEnterFrame = enterFrame;

};

dbg.onEnterFrame = enterFrame;

g.f();

assertEq(errors.length, 1);

assertEq(errors[0].unsafeDereference().toString(),

         "Error: variable 'this' has been optimized out");