Bug Report

🔎 Search Terms

inference, generics, return type

🕗 Version & Regression Information

I'm not sure when this bug "appeared", but it seems to behave this way for every version, even the nightly

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about object property inference with regards to function returns

⏯ Playground Link

https://www.typescriptlang.org/play?ts=4.5.2#code/GYVwdgxgLglg9mABCAzgUwIojQJwJ4A8AKlrngNJp4A0iRAIgIZSMB8AFAPpwAOsCKAFyIA3gChEiAI7Z8lPMJKyKVANwTpygGJhh7CAihoAHlAD8wkZrLzFpOVUQBfAJSIAvKzpMW6yQgBlEAgINBQhRHYAE2ZGRR9GN09EADc4GCj1V1EnMTEDMBQoawc8D0QAbQAiIyKq2gBGWgAmWisAZmEoHGxnAF08gHpBxDA4RAKjU1HxiHwxVExldnFJGRsqag11-B09F2EwEABbACNcDy8mjUDg0PC9GJYkryfGADooOC0YYzQo9guLaudRiYaIRgoRAoOAICFQgCSyHQEygxlob0QMChY0QABsEABzC5wYCIKB4HhoUYnc44RDAOD024hMIoBboex4FbbZTyLZrbS6SLQYwHGlnC7Ja6ScEAdQAFmVsYgAAZvVWIUnkynU1WMMB4VVmG5gIKsh6RN4vRBvT7fX7-QHAlzqIA

💻 Code

function useQuery<TQueryKey, TData>(_options: {
  queryKey: TQueryKey;
  queryFn: (context?: { queryKey: TQueryKey }) => TData;
  onSuccess: (data: TData) => void;
}) {}

const queryKey = ["test", 1, 2, { 3: true }]

// no context no cry
useQuery({
  queryKey,
  queryFn: (): number => 1,
  onSuccess: (data) => data.toFixed(),
});

// as soon as I use ctx, data is no longer of type number for onSuccess
useQuery({
  queryKey,
  queryFn: (ctx): number => 1,
  // Why is `data` of type `any`?
  onSuccess: (data) => data.toFixed(),
});

🙁 Actual behavior

In the second example the data argument on the onSuccess function is typed as any.

🙂 Expected behavior

In the second example the data argument should be typed as the return value of the queryFn property, or more specifically, number