schedule/tracking (production bundle) should not cause react-dom (pro…

…filing bundle) to error

packages/schedule/src/Tracking.js

@@ -65,19 +65,14 @@ let threadIDCounter: number = 0;
 // Interactions "stack"–
 // Meaning that newly tracked interactions are appended to the previously active set.
 // When an interaction goes out of scope, the previous set (if any) is restored.
-let interactionsRef: InteractionsRef = (null: any);
+const interactionsRef: InteractionsRef = {
+  current: new Set(),
+};
 
 // Listener(s) to notify when interactions begin and end.
-let subscriberRef: SubscriberRef = (null: any);
-
-if (enableSchedulerTracking) {
-  interactionsRef = {
-    current: new Set(),
-  };
-  subscriberRef = {
-    current: null,
-  };
-}
+const subscriberRef: SubscriberRef = {
+  current: null,
+};
 
 export {interactionsRef as __interactionsRef, subscriberRef as __subscriberRef};
 

packages/schedule/src/__tests__/Tracking-test.internal.js

@@ -365,11 +365,5 @@ describe('Tracking', () => {
 
       wrappedCallback();
     });
-
-    describe('advanced integration', () => {
-      it('should not create unnecessary objects', () => {
-        expect(SchedulerTracking.__interactionsRef).toBe(null);
-      });
-    });
   });
 });

packages/schedule/src/__tests__/Tracking-test.js

@@ -48,4 +48,13 @@ describe('Tracking', () => {
 
     wrappedCallback();
   });
+
+  // Make sure that accidental pairing of react-dom/profiling production bundle,
+  // With production (non-profiling) schedule/tracking doesn't cause runtime error.
+  it('should always export non-null refs to avoid breaking react-dom/profiling bundle', () => {
+    expect(SchedulerTracking.__interactionsRef).toBeDefined();
+    expect(SchedulerTracking.__interactionsRef).not.toBe(null);
+    expect(SchedulerTracking.__subscriberRef).toBeDefined();
+    expect(SchedulerTracking.__subscriberRef).not.toBe(null);
+  });
 });