fix(client+server): non-records inferred as records

packages/server/src/shared/internal/serialize.ts

@@ -18,6 +18,8 @@ type IsAny<T> = 0 extends T & 1 ? true : false;
 // support it as both a Primitive and a NonJsonPrimitive
 type JsonReturnable = JsonPrimitive | undefined;
 
+type IsRecord<T> = keyof WithoutIndexSignature<T> extends never ? true : false;
+
 /* prettier-ignore */
 export type Serialize<T> =
   IsAny<T> extends true ? any :
@@ -29,7 +31,7 @@ export type Serialize<T> =
   T extends [] ? [] :
   T extends [unknown, ...unknown[]] ? SerializeTuple<T> :
   T extends readonly (infer U)[] ? (U extends NonJsonPrimitive ? null : Serialize<U>)[] :
-  Record<never, never> extends T ? Record<keyof T, Serialize<T[keyof T]>> :
+  IsRecord<T> extends true ? Record<keyof T, Serialize<T[keyof T]>> :
   T extends object ? Simplify<SerializeObject<UndefinedToOptional<T>>> :
   never;
 

packages/tests/server/regression/issue-5075-complex-zod-serialized-inference.test.ts

@@ -0,0 +1,42 @@
+import { inferRouterOutputs, initTRPC } from '@trpc/server';
+import * as z from 'zod';
+
+describe('Non-records should not erroneously be inferred as Records in serialized types', () => {
+  const zChange = z.object({
+    status: z
+      .tuple([
+        z.literal('tmp').or(z.literal('active')),
+        z.literal('active').or(z.literal('disabled')),
+      ])
+      .optional(),
+    validFrom: z.tuple([z.string().nullable(), z.string()]).optional(),
+    validTo: z.tuple([z.string().nullable(), z.string().nullable()]).optional(),
+    canceled: z.tuple([z.boolean(), z.boolean()]).optional(),
+    startsAt: z
+      .tuple([z.string().nullable(), z.string().nullable()])
+      .optional(),
+    endsAt: z.tuple([z.string().nullable(), z.string().nullable()]).optional(),
+  });
+  type Change = z.infer<typeof zChange>;
+
+  test('should be inferred as object', () => {
+    const t = initTRPC.create();
+
+    const router = t.router({
+      createProject: t.procedure.output(zChange).query(() => {
+        return zChange.parse(null as any);
+      }),
+      createProjectNoExplicitOutput: t.procedure.query(() => {
+        return zChange.parse(null as any);
+      }),
+    });
+
+    type SerializedOutput = inferRouterOutputs<typeof router>['createProject'];
+    type SerializedOutputNoExplicitOutput = inferRouterOutputs<
+      typeof router
+    >['createProjectNoExplicitOutput'];
+
+    expectTypeOf<SerializedOutput>().toEqualTypeOf<Change>();
+    expectTypeOf<SerializedOutputNoExplicitOutput>().toEqualTypeOf<Change>();
+  });
+});