From ace8497ca6777fb41c64d68e7366f16fcbdb1342 Mon Sep 17 00:00:00 2001
From: Stan Wohlwend <n2d4xc@gmail.com>
Date: Sun, 16 Jun 2024 15:55:37 +0200
Subject: [PATCH] Reduce occurence of "A component was suspended by an uncached
 promise"

---
 packages/stack-shared/src/utils/promises.tsx | 28 ++++++++++++++++----
 packages/stack/src/lib/stack-app.ts          |  6 ++++-
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/packages/stack-shared/src/utils/promises.tsx b/packages/stack-shared/src/utils/promises.tsx
index 71f61d50f..6bc595246 100644
--- a/packages/stack-shared/src/utils/promises.tsx
+++ b/packages/stack-shared/src/utils/promises.tsx
@@ -1,4 +1,5 @@
 import { StackAssertionError, captureError } from "./errors";
+import { DependenciesMap } from "./maps";
 import { Result } from "./results";
 import { generateUuid } from "./uuids";
 
@@ -38,28 +39,45 @@ export function createPromise<T>(callback: (resolve: Resolve<T>, reject: Reject)
   } as any);
 }
 
+const resolvedCache = new DependenciesMap<[unknown], ReactPromise<unknown>>();
 /**
- * Like Promise.resolve(...), but also adds the status and value properties for use with React's `use` hook.
+ * Like Promise.resolve(...), but also adds the status and value properties for use with React's `use` hook, and caches
+ * the value so that invoking `resolved` twice returns the same promise.
  */
 export function resolved<T>(value: T): ReactPromise<T> {
-  return Object.assign(Promise.resolve(value), {
+  if (resolvedCache.has([value])) {
+    return resolvedCache.get([value]) as ReactPromise<T>;
+  }
+
+  const res = Object.assign(Promise.resolve(value), {
     status: "fulfilled",
     value,
   } as const);
+  resolvedCache.set([value], res);
+  return res;
 }
 
+const rejectedCache = new DependenciesMap<[unknown], ReactPromise<unknown>>();
 /**
- * Like Promise.resolve(...), but also adds the status and value properties for use with React's `use` hook.
+ * Like Promise.reject(...), but also adds the status and value properties for use with React's `use` hook, and caches
+ * the value so that invoking `rejected` twice returns the same promise.
  */
 export function rejected<T>(reason: unknown): ReactPromise<T> {
-  return Object.assign(Promise.reject(reason), {
+  if (rejectedCache.has([reason])) {
+    return rejectedCache.get([reason]) as ReactPromise<T>;
+  }
+
+  const res = Object.assign(Promise.reject(reason), {
     status: "rejected",
     reason: reason,
   } as const);
+  rejectedCache.set([reason], res);
+  return res;
 }
 
+const neverResolvePromise = pending(new Promise<never>(() => {}));
 export function neverResolve(): ReactPromise<never> {
-  return pending(new Promise<never>(() => {}));
+  return neverResolvePromise;
 }
 
 export function pending<T>(promise: Promise<T>, options: { disableErrorWrapping?: boolean } = {}): ReactPromise<T> {
diff --git a/packages/stack/src/lib/stack-app.ts b/packages/stack/src/lib/stack-app.ts
index 006390a7c..fa7ef2d7c 100644
--- a/packages/stack/src/lib/stack-app.ts
+++ b/packages/stack/src/lib/stack-app.ts
@@ -198,7 +198,11 @@ function useAsyncCache<D extends any[], T>(cache: AsyncCache<D, T>, dependencies
 
   // note: we must use React.useSyncExternalStore instead of importing the function directly, as it will otherwise
   // throw an error ("can't import useSyncExternalStore from the server")
-  const value = React.useSyncExternalStore(subscribe, getSnapshot, getSnapshot);
+  const value = React.useSyncExternalStore(
+    subscribe,
+    getSnapshot,
+    () => throwErr(new Error("getServerSnapshot should never be called in useAsyncCache because we restrict to CSR earlier"))
+  );
 
   if (value === loadingSentinel) {
     return use(cache.getOrWait(dependencies, "read-write"));