fix: correctly infer deferred types for top-level promises

.changeset/tasty-apricots-doubt.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/server-runtime": patch
+---
+
+correctly infer deferred types for top-level promises

packages/remix-server-runtime/__tests__/serialize-test.ts

@@ -1,52 +1,54 @@
 import type { SerializeFrom } from "../index";
 import { defer, json } from "../index";
-import type { IsNever } from "./utils";
 import { isEqual } from "./utils";
 
-describe("SerializeFrom", () => {
-  it("infers types", () => {
-    isEqual<SerializeFrom<string>, string>(true);
-    isEqual<SerializeFrom<number>, number>(true);
-    isEqual<SerializeFrom<boolean>, boolean>(true);
-    isEqual<SerializeFrom<String>, String>(true);
-    isEqual<SerializeFrom<Number>, Number>(true);
-    isEqual<SerializeFrom<Boolean>, Boolean>(true);
-    isEqual<SerializeFrom<null>, null>(true);
-
-    isEqual<IsNever<SerializeFrom<undefined>>, true>(true);
-    isEqual<IsNever<SerializeFrom<Function>>, true>(true);
-    isEqual<IsNever<SerializeFrom<symbol>>, true>(true);
-
-    isEqual<SerializeFrom<[]>, []>(true);
-    isEqual<SerializeFrom<[string, number]>, [string, number]>(true);
-    isEqual<SerializeFrom<[number, number]>, [number, number]>(true);
-
-    isEqual<SerializeFrom<ReadonlyArray<string>>, string[]>(true);
-    isEqual<SerializeFrom<ReadonlyArray<Function>>, null[]>(true);
-
-    isEqual<SerializeFrom<{ hello: "remix" }>, { hello: "remix" }>(true);
-    isEqual<
-      SerializeFrom<{ data: { hello: "remix" } }>,
-      { data: { hello: "remix" } }
-    >(true);
-  });
+it("infers basic types", () => {
+  isEqual<
+    SerializeFrom<{
+      hello?: string;
+      count: number | undefined;
+      date: Date | number;
+      isActive: boolean;
+      items: { name: string; price: number; orderedAt: Date }[];
+    }>,
+    {
+      hello?: string;
+      count?: number;
+      date: string | number;
+      isActive: boolean;
+      items: { name: string; price: number; orderedAt: string }[];
+    }
+  >(true);
+});
 
-  it("infers type from json responses", () => {
-    let loader = () => json({ hello: "remix" });
-    isEqual<SerializeFrom<typeof loader>, { hello: string }>(true);
+it("infers deferred types", () => {
+  let get = (): Promise<Date> | undefined => {
+    if (Math.random() > 0.5) return Promise.resolve(new Date());
+    return undefined;
+  };
+  let loader = async () =>
+    defer({
+      critical: await Promise.resolve("hello"),
+      deferred: get(),
+    });
+  isEqual<
+    SerializeFrom<typeof loader>,
+    {
+      critical: string;
+      deferred: Promise<string> | undefined;
+    }
+  >(true);
+});
 
-    let asyncLoader = async () => json({ hello: "remix" });
-    isEqual<SerializeFrom<typeof asyncLoader>, { hello: string }>(true);
-  });
+it("infers types from json", () => {
+  let loader = () => json({ data: "remix" });
+  isEqual<SerializeFrom<typeof loader>, { data: string }>(true);
 
-  it("infers type from defer responses", () => {
-    let loader = async () => defer({ data: { hello: "remix" } });
-    isEqual<SerializeFrom<typeof loader>, { data: { hello: string } }>(true);
-  });
+  let asyncLoader = async () => json({ data: "remix" });
+  isEqual<SerializeFrom<typeof asyncLoader>, { data: string }>(true);
+});
 
-  // Special case that covers https://github.com/remix-run/remix/issues/5211
-  it("infers type from json responses containing a data key", () => {
-    let loader = async () => json({ data: { hello: "remix" } });
-    isEqual<SerializeFrom<typeof loader>, { data: { hello: string } }>(true);
-  });
+it("infers type from defer", () => {
+  let loader = async () => defer({ data: "remix" });
+  isEqual<SerializeFrom<typeof loader>, { data: string }>(true);
 });

packages/remix-server-runtime/__tests__/utils.ts

@@ -93,5 +93,3 @@ export function prettyHtml(source: string): string {
 export function isEqual<A, B>(
   arg: A extends B ? (B extends A ? true : false) : false
 ): void {}
-
-export type IsNever<T> = [T] extends [never] ? true : false;

packages/remix-server-runtime/serialize.ts

@@ -4,35 +4,38 @@ import type { AppData } from "./data";
 import type { TypedDeferredData, TypedResponse } from "./responses";
 
 // Note: The return value has to be `any` and not `unknown` so it can match `void`.
-type ArbitraryFunction = (...args: any[]) => any;
-type NotJsonable = ArbitraryFunction | undefined | symbol;
-
-type Serialize<T> = T extends TypedDeferredData<infer U>
-  ? SerializeDeferred<U>
-  : Jsonify<T>;
+type Fn = (...args: any[]) => any;
 
 // prettier-ignore
-type SerializeDeferred<T extends Record<string, unknown>> = {
-  [k in keyof T as
-    T[k] extends Promise<unknown> ? k :
-    T[k] extends NotJsonable ? never :
-    k
-  ]:
-    T[k] extends Promise<infer U>
-    ? Promise<Serialize<U>> extends never ? "wtf" : Promise<Serialize<U>>
-    : Serialize<T[k]>  extends never ? k : Serialize<T[k]>;
-};
-
 /**
  * Infer JSON serialized data type returned by a loader or action.
  *
  * For example:
  * `type LoaderData = SerializeFrom<typeof loader>`
  */
-export type SerializeFrom<T extends AppData | ArbitraryFunction> = Serialize<
-  T extends (...args: any[]) => infer Output
-    ? Awaited<Output> extends TypedResponse<infer U>
-      ? U
-      : Awaited<Output>
-    : Awaited<T>
->;
+export type SerializeFrom<T extends AppData | Fn> =
+  T extends (...args: any[]) => infer Output ?
+    Awaited<Output> extends TypedResponse<infer U> ? Jsonify<U> :
+    Awaited<Output> extends TypedDeferredData<infer U> ?
+      // top-level promises
+      & {
+        [K in keyof U as
+          K extends symbol ? never :
+          Promise<any> extends U[K] ? K :
+          never
+        ]:
+        // use generic to distribute over union
+        DeferValue<U[K]>
+      }
+      // non-promises
+      & Jsonify<{ [K in keyof U as Promise<any> extends U[K] ? never : K]: U[K] }>
+      :
+    Jsonify<Awaited<Output>> :
+  Jsonify<Awaited<T>>
+;
+
+// prettier-ignore
+type DeferValue<T> =
+  T extends undefined ? undefined :
+  T extends Promise<unknown> ? Promise<Jsonify<Awaited<T>>> :
+  Jsonify<T>;