setQueryData: NoInfer loses discriminated-union members when spreading a narrowed updater value

[ryoid]

Describe the bug

With @tanstack/react-query@5.104.0, setQueryData infers the correct data type from a queryOptions key, but narrowing and spreading that union inside the updater produces a false assignability error. Explicitly annotating the updater parameter as Data | undefined makes the same code compile.

Minimal reproduction

import { QueryClient, queryOptions } from '@tanstack/react-query';

type Data =
  | { kind: 'a'; value: number; requiredA: number }
  | { kind: 'b'; value: number; requiredB: number };

const query = queryOptions({
  queryKey: ['probe'],
  queryFn: async (): Promise<Data> => ({ kind: 'a', value: 1, requiredA: 1 }),
});
const client = new QueryClient();

client.setQueryData(query.queryKey, (prev) => {
  if (!prev || prev.kind !== 'a') return prev;
  return { ...prev, value: prev.value + 1 };
});

Run with TypeScript 5.8.3:

tsc --noEmit --strict --skipLibCheck --target es2023 --moduleResolution bundler --module esnext repro.ts

Actual behavior

TS2345: the callback return is inferred as NoInfer<Data> | { value: number; kind: 'a' | 'b' } | undefined. The spread loses the variant-specific required fields, so the returned object is rejected as Data.

Expected behavior

After the guard, spreading prev should preserve kind: 'a' and requiredA. The updater should compile without repeating the data type already encoded in the query key.

Workaround

Changing only (prev) to (prev: Data | undefined) compiles.

Versions and related context

• @tanstack/react-query: 5.104.0
• TypeScript: 5.8.3
• Reproduces during typechecking; no browser or network calls needed.

Related: #11018 and #11245 address the useQuery return type. This report concerns the remaining NoInfer interaction in QueryClient.setQueryData updater parameters. The inferred key type itself is correct; the failure occurs during union narrowing/spread.