fix: distribute over union types with promises

remix-run · Aug 8, 2023 · 0ffe817 · 0ffe817
1 parent 267d6bc
commit 0ffe817
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Showing 2 changed files with 10 additions and 3 deletions.
diff --git a/packages/remix-server-runtime/__tests__/serialize-test.ts b/packages/remix-server-runtime/__tests__/serialize-test.ts
@@ -22,8 +22,8 @@ it("infers basic types", () => {
 });
 
 it("infers deferred types", () => {
-  let get = (): Promise<string> | undefined => {
-    if (Math.random() > 0.5) return Promise.resolve("hello");
+  let get = (): Promise<Date> | undefined => {
+    if (Math.random() > 0.5) return Promise.resolve(new Date());
     return undefined;
   };
   let loader = async () =>

diff --git a/packages/remix-server-runtime/serialize.ts b/packages/remix-server-runtime/serialize.ts
@@ -24,11 +24,18 @@ export type SerializeFrom<T extends AppData | Fn> =
           Promise<any> extends U[K] ? K :
           never
         ]:
-        U[K] extends Promise<any> ? Promise<Jsonify<Awaited<U[K]>>> : Jsonify<U[K]>
+        // 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>;