Wrap all alert payloads in useMemo to avoid infinite re-rendering (#182)

* Wrap all alert payloads in useMemo to avoid infinite re-rendering

This manifested in production as a browser freeze for any
user who saw the 15%-off-to-upgrade message.

TNL-7400

* fixup! meant to say identity, not equality

src/alerts/access-expiration-alert/hooks.js

@@ -7,11 +7,9 @@ function useAccessExpirationAlert(courseExpiredMessage, topic) {
   const rawHtml = courseExpiredMessage || null;
   const isVisible = !!rawHtml; // If it exists, show it.
 
-  const payload = useMemo(() => ({ rawHtml }), [rawHtml]);
-
   useAlert(isVisible, {
     code: 'clientAccessExpirationAlert',
-    payload,
+    payload: useMemo(() => ({ rawHtml }), [rawHtml]),
     topic,
   });
 

src/alerts/enrollment-alert/hooks.js

@@ -1,6 +1,6 @@
 /* eslint-disable import/prefer-default-export */
 import React, {
-  useContext, useState, useCallback,
+  useContext, useState, useCallback, useMemo,
 } from 'react';
 
 import { UserMessagesContext, ALERT_TYPES, useAlert } from '../../generic/user-messages';
@@ -14,15 +14,16 @@ export function useEnrollmentAlert(courseId) {
   const course = useModel('courses', courseId);
   const outline = useModel('outline', courseId);
   const isVisible = course && course.isEnrolled !== undefined && !course.isEnrolled;
+  const payload = {
+    canEnroll: outline.enrollAlert.canEnroll,
+    courseId,
+    extraText: outline.enrollAlert.extraText,
+    isStaff: course.isStaff,
+  };
 
   useAlert(isVisible, {
     code: 'clientEnrollmentAlert',
-    payload: {
-      canEnroll: outline.enrollAlert.canEnroll,
-      courseId,
-      extraText: outline.enrollAlert.extraText,
-      isStaff: course.isStaff,
-    },
+    payload: useMemo(() => payload, Object.values(payload).sort()),
     topic: 'outline',
   });
 

src/alerts/offer-alert/hooks.js

@@ -1,4 +1,4 @@
-import React from 'react';
+import React, { useMemo } from 'react';
 import { useAlert } from '../../generic/user-messages';
 
 const OfferAlert = React.lazy(() => import('./OfferAlert'));
@@ -10,7 +10,7 @@ export function useOfferAlert(offerHtml, topic) {
   useAlert(isVisible, {
     code: 'clientOfferAlert',
     topic,
-    payload: { rawHtml },
+    payload: useMemo(() => ({ rawHtml }), [rawHtml]),
   });
 
   return { clientOfferAlert: OfferAlert };

src/course-home/outline-tab/alerts/certificate-available-alert/hooks.js

@@ -1,4 +1,4 @@
-import React from 'react';
+import React, { useMemo } from 'react';
 import { getAuthenticatedUser } from '@edx/frontend-platform/auth';
 
 import { useAlert } from '../../../../generic/user-messages';
@@ -23,14 +23,15 @@ function useCertificateAvailableAlert(courseId) {
   const endDate = endBlock ? new Date(endBlock.date) : null;
   const hasEnded = endBlock ? endDate < new Date() : false;
   const isVisible = isEnrolled && certBlock && hasEnded; // only show if we're between end and cert dates
+  const payload = {
+    certDate: certBlock && certBlock.date,
+    username,
+    userTimezone,
+  };
 
   useAlert(isVisible, {
     code: 'clientCertificateAvailableAlert',
-    payload: {
-      certDate: certBlock && certBlock.date,
-      username,
-      userTimezone,
-    },
+    payload: useMemo(() => payload, Object.values(payload).sort()),
     topic: 'outline-course-alerts',
   });
 

src/course-home/outline-tab/alerts/course-end-alert/hooks.js

@@ -1,5 +1,5 @@
 /* eslint-disable import/prefer-default-export */
-import React from 'react';
+import React, { useMemo } from 'react';
 import { useAlert } from '../../../../generic/user-messages';
 import { useModel } from '../../../../generic/model-store';
 
@@ -23,15 +23,16 @@ export function useCourseEndAlert(courseId) {
   const endDate = endBlock ? new Date(endBlock.date) : null;
   const delta = endBlock ? endDate - new Date() : 0;
   const isVisible = isEnrolled && endBlock && delta > 0 && delta < WARNING_PERIOD_MS;
+  const payload = {
+    delta,
+    description: endBlock && endBlock.description,
+    endDate: endBlock && endBlock.date,
+    userTimezone,
+  };
 
   useAlert(isVisible, {
     code: 'clientCourseEndAlert',
-    payload: {
-      delta,
-      description: endBlock && endBlock.description,
-      endDate: endBlock && endBlock.date,
-      userTimezone,
-    },
+    payload: useMemo(() => payload, Object.values(payload).sort()),
     topic: 'outline-course-alerts',
   });
 

src/generic/user-messages/hooks.js

@@ -8,6 +8,17 @@ export function useAlert(isVisible, {
   const { add, remove } = useContext(UserMessagesContext);
   const [alertId, setAlertId] = useState(null);
 
+  // Please note:
+  // The deps list [isVisible, code, ... etc.] in this `useEffect` call prevents the
+  // effect from running if none of deps have changed. However, "changed" for objects is
+  // defined in terms of identity; thus, if you provide a payload that is *seemingly* equal
+  // to the previous one but *actually* a different object, then this effect will run.
+  // If you are particularly unlucky, this will cause an infinite re-render loop.
+  // This manifested itself in TNL-7400.
+  // We hope to address the underlying issue in TNL-7418.
+  // In the mean time, you may follow the pattern that `useAccessExpirationAlert`
+  // establishes: memoize the payload so that the exact same object is used if the
+  // payload has not changed.
   useEffect(() => {
     if (isVisible && alertId === null) {
       setAlertId(add({