Update LiveMap.get to have undefined as a possible return value

This is a temporary solution for handling the access API for tombstoned
objects. See comment in Confluence for the relevant discussion [1].

The return type for the LiveCounter.value is not changed as part of this
commit, as the tombstoned LiveCounter has a value of 0 for its data.

[1] https://ably.atlassian.net/wiki/spaces/LOB/pages/3556671496/LODR-026+Correctness+of+OBJECT_DELETE?focusedCommentId=3593928705

ably.d.ts

@@ -2105,10 +2105,12 @@ export declare interface LiveMap<T extends LiveMapType> extends LiveObject<LiveM
   /**
    * Returns the value associated with a given key. Returns `undefined` if the key doesn't exist in a map or if the associated {@link LiveObject} has been deleted.
    *
+   * Always returns undefined if this map object is deleted.
+   *
    * @param key - The key to retrieve the value for.
-   * @returns A {@link LiveObject}, a primitive type (string, number, boolean, or binary data) or `undefined` if the key doesn't exist in a map or the associated {@link LiveObject} has been deleted.
+   * @returns A {@link LiveObject}, a primitive type (string, number, boolean, or binary data) or `undefined` if the key doesn't exist in a map or the associated {@link LiveObject} has been deleted. Always `undefined` if this map object is deleted.
    */
-  get<TKey extends keyof T & string>(key: TKey): T[TKey] extends StateValue ? T[TKey] : T[TKey] | undefined;
+  get<TKey extends keyof T & string>(key: TKey): T[TKey] | undefined;
 
   /**
    * Returns the number of key/value pairs in the map.

src/plugins/liveobjects/livemap.ts

@@ -80,12 +80,13 @@ export class LiveMap<T extends API.LiveMapType> extends LiveObject<LiveMapData,
    *
    * - If no entry is associated with the specified key, `undefined` is returned.
    * - If map entry is tombstoned (deleted), `undefined` is returned.
+   * - If this map object is tombstoned, `undefined` is returned.
    * - If the value associated with the provided key is an objectId string of another Live Object, a reference to that Live Object
    * is returned, provided it exists in the local pool and is not tombstoned. Otherwise, `undefined` is returned.
    * - If the value is not an objectId, then that value is returned.
    */
   // force the key to be of type string as we only allow strings as key in a map
-  get<TKey extends keyof T & string>(key: TKey): T[TKey] extends StateValue ? T[TKey] : T[TKey] | undefined {
+  get<TKey extends keyof T & string>(key: TKey): T[TKey] | undefined {
     const element = this._dataRef.data.get(key);
 
     if (element === undefined) {

test/package/browser/template/src/index-liveobjects.ts

@@ -24,14 +24,14 @@ globalThis.testAblyPackage = async function () {
   const size: number = root.size();
 
   // check custom user provided typings via LiveObjectsTypes are working:
+  // any LiveMap.get() call can return undefined, as the LiveMap itself can be tombstoned (has empty state),
+  // or referenced object is tombstoned.
   // keys on a root:
-  const aNumber: number = root.get('numberKey');
-  const aString: string = root.get('stringKey');
-  const aBoolean: boolean = root.get('booleanKey');
-  const couldBeUndefined: string | undefined = root.get('couldBeUndefined');
+  const aNumber: number | undefined = root.get('numberKey');
+  const aString: string | undefined = root.get('stringKey');
+  const aBoolean: boolean | undefined = root.get('booleanKey');
+  const userProvidedUndefined: string | undefined = root.get('couldBeUndefined');
   // live objects on a root:
-  // LiveMap.get can still return undefined for LiveObject typed properties even if custom typings have them as non-optional.
-  // objects can be tombstoned and result in the undefined value
   const counter: Ably.LiveCounter | undefined = root.get('counterKey');
   const map: LiveObjectsTypes['root']['mapKey'] | undefined = root.get('mapKey');
   // check string literal types works
@@ -63,5 +63,5 @@ globalThis.testAblyPackage = async function () {
 
   // check can provide custom types for the getRoot method, ignoring global LiveObjectsTypes interface
   const explicitRoot: Ably.LiveMap<ExplicitRootType> = await liveObjects.getRoot<ExplicitRootType>();
-  const someOtherKey: string = explicitRoot.get('someOtherKey');
+  const someOtherKey: string | undefined = explicitRoot.get('someOtherKey');
 };