equatable-linkedhashmap-lru-reorder

Equatable + LinkedHashMap LRU reorder suppression

Problem

A Flutter bloc/cubit state class uses an insertion-ordered LinkedHashMap<K, V> to implement LRU semantics (touch-on-access, evict oldest past a cap). The field is included in props for value equality. When an existing key is re-inserted to move it to most-recent, Cubit.emit drops the new state as equal to the previous one, leaving LRU order stale. On the next insert past the cap, the "touched" entry is evicted instead of the truly oldest one.

This is silent: no errors, no logs. Tests that only check the final status of each key pass. The bug surfaces only when a test specifically asserts that a refreshed key survives a later cap-overflow eviction.

Context / Trigger Conditions

• State class extends Equatable with a LinkedHashMap<K, V> field
• LRU behavior implemented via remove(key) + insert to move-to-most-recent
• props includes the map directly: List<Object?> get props => [_map, ...]
• Symptoms:
  • blocTest(..., expect: () => hasLength(N)) reports fewer emissions than expected
  • LRU eviction test like "refresh key A, then overflow — expect B evicted" fails with A evicted instead
  • Consumers using BlocListener or context.select don't react to touch-only updates

Solution

Add the keys list to props alongside the map so insertion-order changes produce a distinct state:

@override
List<Object?> get props {
  // Both entries are required.
  //
  // Equatable's default map comparison is structural (unordered), so
  // `_statuses` alone catches value changes but NOT pure LRU reorders
  // where the key/value set is unchanged.
  // `_statuses.keys.toList()` catches those insertion-order changes.
  // Removing either would silently suppress a whole class of state
  // updates — do not "simplify" this.
  return [_statuses, _statuses.keys.toList(), maxEntries];
}

Keep the map in props as well — it catches value-only changes (same key, different value, no reorder). The keys list catches order-only changes. Together they cover both dimensions. Removing either re-opens the bug.