JSTests/test262/test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js

// Copyright (C) 2019 Google. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.
/*---
esid: sec-array.prototype.copywithin
description: >
  SECURITY: start argument is coerced to an integer value
  and side effects change the length of the array so that
  the target is out of bounds
info: |
  22.1.3.3 Array.prototype.copyWithin (target, start [ , end ] )

  ...
  8. Let relativeStart be ToInteger(start).
  ...
includes: [compareArray.js]
---*/


// make a long integer Array
function longDenseArray(){
	var a = [0];
	for(var i = 0; i < 1024; i++){
		a[i] = i;
	}
	return a;
}

function shorten(){
	currArray.length = 20;
	return 1;
}

var array = longDenseArray();
array.length = 20;
for(var i = 0; i < 19; i++){
	array[i+1000] = array[i+1];
}

var currArray = longDenseArray();

assert(
  compareArray(
    currArray.copyWithin(1000, {valueOf: shorten}), array
  ),
  'coercion side-effect makes target out of bounds'
);