Temporal: Add coverage for modified Array iteration when called from CalendarFields/GetPossibleInstantsFor

[anba]

It'd be nice to have coverage when the built-in Array iteration has been modified to ensure implementations correctly handle this case in CalendarFields and GetPossibleInstantsFor.

CalendarFields:

let observed = [];
let ArrayIterProto = Object.getPrototypeOf([][Symbol.iterator]());
let oldNext = ArrayIterProto.next;
ArrayIterProto.next = function() {
  var r = oldNext.call(this);
  if (!r.done) {
    observed.push(r.value);
  }
  return r;
};

// No overridden `fields` methods, but calling CalendarFields is still observable through
// modified Array iteration.
let calendar = new Temporal.Calendar("iso8601");

let pd = new Temporal.PlainDate(2000, 1, 1, calendar).with({year: 2001});

// Should output: day,month,monthCode,year,day,month,monthCode,year
console.log(observed);

GetPossibleInstantsFor:

let observed = [];
let ArrayIterProto = Object.getPrototypeOf([][Symbol.iterator]());
let oldNext = ArrayIterProto.next;
ArrayIterProto.next = function() {
  var r = oldNext.call(this);
  if (!r.done) {
    observed.push(r.value);
  }
  return r;
};

// No overridden `getPossibleInstantsFor` methods, but calling GetPossibleInstantsFor is still
// observable through modified Array iteration.
let timeZone = new Temporal.TimeZone("UTC");

let pd = new Temporal.PlainDate(2000, 1, 1);
let zdt = pd.toZonedDateTime(timeZone);

// Should print: 2000-01-01T00:00:00Z
// Note: `observed[0]` is a Temporal.Instant value.
console.log(observed);

[ptomato]

This may be obsoleted by tc39/proposal-temporal#2519? I haven't checked yet.

[ptomato]

After tc39/proposal-temporal#2657 we'll have no observable array iteration if the called fields method is from a built-in calendar. It's already the case that we have no observable array iteration if the called getPossibleInstantsFor method is from a built-in time zone.

ed3a092 adds coverage for builtin fields not observably calling Array.prototype[Symbol.iterator].

So, to fulfill this issue we would still need to add coverage for:

• builtin getPossibleInstantsFor not observably calling Array.prototype[Symbol.iterator]
• return value of custom calendar fields being observably iterated
• return value of custom time zone getPossibleInstantsFor being observably iterated