Function whyNotUpdated

whyNotUpdated<T>(
prev: ResourceState<T>,
next: ResourceState<T>,
): null | WhyNotUpdatedReason
Decode the reason a subscriber did NOT see an update on a given commit. Returns one of WhyNotUpdatedReason, or null if the resource actually did transition (prev !== next structurally).
Type Parameters
- T
Parameters
- prev: ResourceState<T>
- next: ResourceState<T>
Returns null | WhyNotUpdatedReason
Remarks
Total over the engine's update-suppression logic:
- Reference equality (Object.is) returns 'object-is-deduped' because the engine's Phase B equality cutoff would have suppressed any commit producing a reference-equal next value.
- Structural inequality but no actual update (a different object, different reference, same shape) returns 'no-dep-overlap' — the commit's changedNodes set did not include this node.
- Structural inequality WITH an update (different shape between prev and next) returns null — the dual is undefined here because the resource DID transition.
Per SPEC.async §11.1, the typical "no update" reasons for a resource are the two named in WhyNotUpdatedReason. A future bump that surfaces additional reasons widens this union and the decoder.
- Defined in packages/sync/src/whyUpdated.ts:167