fix(base-controller): Fix stateChange subscriptions with selectors

Subscribers to the `stateChange` event of any `BaseControllerV2`-based
controllers will now correctly handle the initial state change event.

Previously the initial state change would always result in this event
firing, even for subscriptions with selectors where the selected value
has not changed. Additionally, the `previousValue` returned was always
set to `undefined` the first time.

`BaseControllerV2` has been updated to correctly compare with the
previous value even for the first state change. The returned
`previousValue` is also now guaranteed to be correct even for the
initial state change.

Fixes #3701

packages/base-controller/src/BaseControllerV2.test.ts

@@ -296,6 +296,64 @@ describe('BaseController', () => {
     ]);
   });
 
+  it('should notify a subscriber with a selector of state changes', () => {
+    const controllerMessenger = new ControllerMessenger<
+      never,
+      CountControllerEvent
+    >();
+    const controller = new CountController({
+      messenger: getCountMessenger(controllerMessenger),
+      name: 'CountController',
+      state: { count: 0 },
+      metadata: countControllerStateMetadata,
+    });
+    const listener = sinon.stub();
+    controllerMessenger.subscribe(
+      'CountController:stateChange',
+      listener,
+      ({ count }) => {
+        // Selector rounds down to nearest multiple of 10
+        return Math.floor(count / 10);
+      },
+    );
+
+    controller.update(() => {
+      return { count: 10 };
+    });
+
+    expect(listener.callCount).toBe(1);
+    expect(listener.firstCall.args).toStrictEqual([1, 0]);
+  });
+
+  it('should not inform a subscriber of state changes if the selected value is unchanged', () => {
+    const controllerMessenger = new ControllerMessenger<
+      never,
+      CountControllerEvent
+    >();
+    const controller = new CountController({
+      messenger: getCountMessenger(controllerMessenger),
+      name: 'CountController',
+      state: { count: 0 },
+      metadata: countControllerStateMetadata,
+    });
+    const listener = sinon.stub();
+    controllerMessenger.subscribe(
+      'CountController:stateChange',
+      listener,
+      ({ count }) => {
+        // Selector rounds down to nearest multiple of 10
+        return Math.floor(count / 10);
+      },
+    );
+
+    controller.update(() => {
+      // Note that this rounds down to zero, so the selected value is still zero
+      return { count: 1 };
+    });
+
+    expect(listener.callCount).toBe(0);
+  });
+
   it('should inform a subscriber of each state change once even after multiple subscriptions', () => {
     const controllerMessenger = new ControllerMessenger<
       never,

packages/base-controller/src/BaseControllerV2.ts

@@ -154,6 +154,11 @@ export class BaseController<
       `${name}:getState`,
       () => this.state,
     );
+
+    this.messagingSystem.registerInitialEventPayload({
+      eventType: `${name}:stateChange`,
+      getPayload: () => [this.state, []],
+    });
   }
 
   /**

packages/name-controller/src/NameController.test.ts

@@ -13,6 +13,7 @@ const TIME_MOCK = 123;
 
 const MESSENGER_MOCK = {
   registerActionHandler: jest.fn(),
+  registerInitialEventPayload: jest.fn(),
   publish: jest.fn(),
   // TODO: Replace `any` with type
   // eslint-disable-next-line @typescript-eslint/no-explicit-any

packages/signature-controller/src/SignatureController.test.ts

@@ -92,6 +92,7 @@ const requestMock = {
 const createMessengerMock = () =>
   ({
     registerActionHandler: jest.fn(),
+    registerInitialEventPayload: jest.fn(),
     publish: jest.fn(),
     call: jest.fn(),
     // TODO: Replace `any` with type

packages/user-operation-controller/src/UserOperationController.test.ts

@@ -99,6 +99,7 @@ function createMessengerMock() {
     call: jest.fn(),
     publish: jest.fn(),
     registerActionHandler: jest.fn(),
+    registerInitialEventPayload: jest.fn(),
   } as unknown as jest.Mocked<UserOperationControllerMessenger>;
 }
 

packages/user-operation-controller/src/helpers/PendingUserOperationTracker.test.ts

@@ -49,6 +49,7 @@ jest.mock('@metamask/controller-utils', () => ({
 function createMessengerMock() {
   return {
     call: jest.fn(),
+    registerInitialEventPayload: jest.fn(),
   } as unknown as jest.Mocked<UserOperationControllerMessenger>;
 }