fix: correct non-transitive keywordComparator in validation.js

[Suyog241005]

Problem

In lib/keywords/validation.js, the keywordComparator is used to sort compiled keywords so that unevaluatedProperties and unevaluatedItems are evaluated last.

The previous comparator was defined as:

const keywordComparator = (_a, b) => lastKeywords.has(b[0]) ? -1 : 1;

This comparator violates the Array.prototype.sort() contract:

1. It never returns 0 (which signifies equal sorting priority).
2. It is non-transitive and contradictory (e.g., comparing two normal keywords A and B results in A > B and B > A simultaneously).

Because of this, the sorting behavior becomes non-deterministic and engine-dependent. Depending on the JS engine (V8, SpiderMonkey, JSC) or array size, unevaluatedProperties/unevaluatedItems could fail to sort to the end, causing unexpected validation bugs.

Solution

Refactored the comparator to correctly compare both inputs and respect the sort contract:

const keywordComparator = (a, b) => {
  const isA = lastKeywords.has(a[0]);
  const isB = lastKeywords.has(b[0]);
  return isA === isB ? 0 : isA ? 1 : -1;
};

This ensures that:

• Two keywords of the same priority return 0 (stable sorting).
• A keyword that belongs at the end returns 1 when compared to a normal one.
• A keyword that belongs at the end returns -1 when compared from the other side.

[Suyog241005]

Hi @jdesrosiers ,

I noticed a bug in the keyword sorting logic where the custom comparator for unevaluatedProperties and unevaluatedItems violates the standard sorting contract (it never returns 0 and has contradictory results when comparing items of equal priority).

This can cause unstable or incorrect keyword ordering depending on the JavaScript engine. I've submitted a quick PR to fix it using a standard transitive comparator. All linting and tests pass successfully. Let me know what you think!