Bug(or Miss): Array/TypedArray#toSorted seems not requiring stability while *#sort requires.

[LumaKernel]

Description:

Array#sort is defined as stable in ES2019 (10th).
Stable sort for Array.prototype.sort

Array#toSorted is introduced in ES2023 (14th).

In ES2024 (15th), the statements for stability can be found as follows:

• In introduction:

  ECMAScript 2019 introduced a few <OMITTED> Other updates included requiring that Array.prototype.sort be a stable sort, requiring that <OMITTED>

  [Normative] Make Array.prototype.sort stable #1340

• In 23.1.3.30 Array.prototype.sort ( comparefn ):

  This method sorts the elements of this array. The sort must be stable (that is, elements that compare equal must remain in their original order). <OMITTED>

  [Normative] Make Array.prototype.sort stable #1340

• In 23.2.3.29 %TypedArray%.prototype.sort ( comparefn ):

  This is a distinct method that, except as described below, implements the same requirements as those of Array.prototype.sort as defined in 23.1.3.30. <OMITTED>

  So it is indirectly mentioning the requirements for stability of the sort. It's introduced in [Normative] Make %TypedArray%.prototype.sort stable #1433

While them, it seems there're no references to theses stability from toSroted functions. First introduced in #2997
toSorted is just using SortIndexedProperties. But SortIndexedProperties is also not requiring the stability (to me), so currently it seems it's ok to be not stable.

In 23.1.3.30.1 SortIndexedProperties ( obj, len, SortCompare, holes ), there's the requirements for permutation used for the sort, but it's only requiring that any 2 elements which is strictly ordered, is also ordered in the result.

I'm not sure why stability is just mentioned in Array#sort but not in SortIndexedProperties, but I believe that's why this is just missed when toSorted is introduced.

SortIndexedProperties seems just referenced to by 5:

• 23.1.3.30 Array.prototype.sort ( comparefn ) (2)
• 23.1.3.34 Array.prototype.toSorted ( comparefn )
• 23.2.3.29 %TypedArray%.prototype.sort ( comparefn )
• 23.2.3.33 %TypedArray%.prototype.toSorted ( comparefn )

So one idea I can come up with is just moving the stability requirements to SortIndexedProperties.

eshost Output:

If I have chance to see implementations of engines I want to confirm, but now I could think they may share the implementations of sort and toSorted internally. (not sure)

[bakkot]

Thanks for the catch and the detailed report. I'm almost certain this was just an oversight; I've filed #3424 to fix.