Add rc.sortBy custom operator

[ajpallares]

Checklist

• If applicable, unit tests
• If applicable, create follow-up issues for purchases-android and hybrids

Motivation

Ordering a list is the one thing reduce cannot fake: comparing an item against the others in the same collection needs a scope the engine does not expose. Sorting through rc.entries key ordering is the closest workaround, and it collapses duplicate keys and misorders numbers.

Description

{"rc.sortBy": [array, keyExpression]} returns the original items in ascending key order. The key template is evaluated once per item with scope rebound to it, exactly as map does, so rc.rootVar is how a key reaches top-level data.

• Keys must be all strings or all numbers. A mix, or a null/bool/array/object key, throws typeMismatch rather than inventing a cross-type ordering. String keys compare by UTF-16 code unit, as JS and Kotlin do, not by Swift's <.
• Ties keep input order. Swift does not guarantee sorted(by:) is stable, so the tiebreak is explicit.
• Always ascending. A third argument is rejected rather than ignored. To sort descending on a numeric key, negate it: {"-": [0, {"var": "score"}]}.

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Note

Medium Risk
New Rules Engine operator affects predicate evaluation for any rule using rc.sortBy; behavior is heavily specified (UTF-16, stability, errors) but cross-platform parity with Android/hybrids is still a follow-up per the PR checklist.

Overview
Adds rc.sortBy to the Rules Engine so predicates can return an array’s original elements in ascending order by a per-item key expression—addressing cases where reduce or rc.entries ordering cannot compare items in-collection or preserve duplicates.

The operator takes [array, keyExpression]; the key is evaluated with scope rebound to each item (like map), wired through CustomOperators and a new SortByOperator. Keys must be homogeneous strings or numbers (numeric compare for numbers, UTF-16 code unit order for strings to match JS/Kotlin); mixed or invalid types, wrong arity, and non-finite numeric keys throw typeMismatch. Stable ties use explicit index tie-breaking because Swift’s sort is not guaranteed stable. Descending numeric sort is done by negating the key; negating string dates is rejected (NaN).

Conformance coverage adds rc_sort_by.json fixtures and bumps the pinned predicate fixture count 519 → 544.

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[rickvdl]

Nice! Just one concern :)

[RevenueCat-Danger-Bot]

❌ CI Job Failed — run-test-ios-26

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Failed Tests

• StoreKit2TransactionListenerTransactionUpdatesTests/testNotifiesDelegateForExistingTransactions()