Force rewritten eval() to use global scope when original is in global scope.

[ikreymer]

The eval() rewriting can sometimes result in the following scenario:

eval('function test() {}');
...
test();

is rewritten to (simplified) effectively:

(function evalwrapper(x) { eval(rewrite(x)); })('function test() {}')
...
test(); <- test not defined, no longer evaluated in global scope.

The rewriting is done in this way to keep the eval() in this same local scope, but if the eval() is actually in the global scope, ideally, it should be kept there!

Fortunately, it seems that there is a mostly reliable way to detect a function in global scope by checking if arguments.caller.callee is null, eg:

function isGlobalScope() { return !arguments.callee.caller; }

console.log(isGlobalScope()); // global scope, prints 'true'

console.log((function() { return isGlobalScope(); })());  // in function declaration, prints 'false'

console.log((() => isGlobalScope())()); // in arrow function, prints 'false'

The above seems to work in Chrome and Firefox. In Safari 14.x, the last one also prints 'true', so there is at least one false positive. However, this seems to be fixed in Safari 15.x.

As an additional sanity checked, the this can also be checked to ensure that it matches the current window (as an additional guard for arrow function false positive).

Also fortunately, the eval() automatically evaluates in the global scope if eval is called indirectly after assignment.
This allows for this kind of setup:

function wrappedEval(x, isGlobal) {
  var eg = eval;
   return isGlobal ? eg(x) : eval(x);
}

This PR implements this functionality, along with change in server-side rewriting which rewrites:
eval(... -> .eval(this, !arguments.callee.caller, ....

I think this should work w/o breaking anything, but want to leave this up for any feedback..

(Sample site fixed by this: http://svlavra.dn.ua/)

[ikreymer]

See webrecorder/wabac.js#71 for corresponding fixes in wabac.js

It adds rewriting of:
eval(x) to
WB_wombat_runEval2((_______eval_arg, isGlobal) => { var ge = eval; return isGlobal ? ge(_______eval_arg) : eval(_______eval_arg); }).eval(this, (function() { return !arguments.callee.caller })(),x)

by prepending additional arguments and a new function call.
(And fortunately, in case of no args,.eval(this, !arguments.callee.caller,) is also valid)

[ikreymer]

In strict mode, arguments.callee access will throw an exception, so instead rewriting:

eval(x) =>

WB_wombat_runEval2((_______eval_arg, isGlobal) => { var ge = eval; return isGlobal ? ge(_______eval_arg) : eval(_______eval_arg); }).eval(this, (function() { return arguments })(),x)

and handling the args.callee.caller in a try/catch block