Fixed an issue with rehydrated actors not registering themselves in t…

…he system (#4403)

.changeset/three-grapes-beg.md

@@ -0,0 +1,5 @@
+---
+'xstate': patch
+---
+
+Fixed an issue with rehydrated actors not registering themselves in the system.

packages/core/src/State.ts

@@ -313,7 +313,8 @@ export function getPersistedState<
     }
     childrenJson[id as keyof typeof childrenJson] = {
       state: child.getPersistedState(),
-      src: child.src
+      src: child.src,
+      systemId: child._systemId
     };
   }
 

packages/core/src/StateMachine.ts

@@ -585,7 +585,7 @@ export class StateMachine<
     const children: Record<string, AnyActorRef> = {};
     const snapshotChildren: Record<
       string,
-      { src: string; state: Snapshot<unknown> }
+      { src: string; state: Snapshot<unknown>; systemId?: string }
     > = (snapshot as any).children;
 
     Object.keys(snapshotChildren).forEach((actorId) => {
@@ -605,7 +605,8 @@ export class StateMachine<
       const actorRef = createActor(logic, {
         id: actorId,
         parent: _actorCtx?.self,
-        state: actorState
+        state: actorState,
+        systemId: actorData.systemId
       });
 
       children[actorId] = actorRef;

packages/core/test/rehydration.test.ts

@@ -169,4 +169,60 @@ describe('rehydration', () => {
 
     expect(rehydratedActor.getSnapshot().value).toBe('c');
   });
+
+  it('a rehydrated active child should be registered in the system', () => {
+    const machine = createMachine(
+      {
+        context: ({ spawn }) => {
+          spawn('foo', {
+            systemId: 'mySystemId'
+          });
+          return {};
+        }
+      },
+      {
+        actors: {
+          foo: createMachine({})
+        }
+      }
+    );
+
+    const actor = createActor(machine).start();
+    const persistedState = actor.getPersistedState();
+    actor.stop();
+
+    const rehydratedActor = createActor(machine, {
+      state: persistedState
+    }).start();
+
+    expect(rehydratedActor.system.get('mySystemId')).not.toBeUndefined();
+  });
+
+  it('a rehydrated done child should not be registered in the system', () => {
+    const machine = createMachine(
+      {
+        context: ({ spawn }) => {
+          spawn('foo', {
+            systemId: 'mySystemId'
+          });
+          return {};
+        }
+      },
+      {
+        actors: {
+          foo: createMachine({ type: 'final' })
+        }
+      }
+    );
+
+    const actor = createActor(machine).start();
+    const persistedState = actor.getPersistedState();
+    actor.stop();
+
+    const rehydratedActor = createActor(machine, {
+      state: persistedState
+    }).start();
+
+    expect(rehydratedActor.system.get('mySystemId')).toBeUndefined();
+  });
 });