'structuralSharing' has incorrect type when combined with 'select'

[levidrain]

Describe the bug

When using both select and structuralSharing, structuralSharing is incorrectly typed to the query result instead of the result of the select parameter.

Your minimal, reproducible example

https://www.typescriptlang.org/play?ts=4.9.5#code/JYWwDg9gTgLgBAbzgVwM4FMCKz1QJ4A0c2ueA0uoXAKoYn4DyYMwEAdqnAL5wBmUEEHADkAARgBDDpIDGAawD0UdBJkwAtAEcc+YQG4AsAChjvZGzWs2cAGIQIACgCUiY3Hco6OvA4RuPAdqkFHgAXHAA2gBEcpRRALoE-gHuQfg2bOESqHgWcM5wALwAfHASAO4SwPBRABLoADYNEHAA6tANACZRSUYpHhgN6GrhqDBQRaVjUAB0Q2wA5jAAFr397tPIashQEg0AyssSUMCL4Q4SRABGLiWufesBCgpwbBAsMuhwKxLwK1+oYALNi-HZfCC8b7LYCcGHfPBgdCdb4taanBbXZDwarCTiqGDIPYNPBwMDZDDI-6vZAgK64PgCISDYYwZKPODKAlQaxRKKGB79LhsrhOflcIA

Steps to reproduce

Create a query with both a select and structualSharing. The select should return a different type from the queryFn.

Expected behavior

The structuralSharing function is typed to accept the queryFn return, but is actually passed the select return.

How often does this bug happen?

Every time

Screenshots or Videos

No response

Platform

• Typescript 4.9.5
• VS Code

Tanstack Query adapter

react-query

TanStack Query version

4.29.3

TypeScript version

4.9.5

Additional context

No response

[TkDodo]

yeah, structuralSharing is applied to both the result of the queryFn as well as the result of select.

I think it would be best to widen the types of structuralSharing to a: unknown, b: unknown. Imo, if a custom structuralSharing is implemented, it's something that you'd usually do on a global level for all queries / some queries that have a specific key anyways.

would that work for you? would you want to contribute it ?

[levidrain]

I added console logs to the structuralSharing callback and it appears to only call this function with the post select data.

In my case, I have an endpoint that gets polled and I only want the change the returned instance if the data has changed. I only need the behavior for this one endpoint and honestly, isDataEqual is a better solution for me, but since it's deprecated, I tried to use structualSharing; but since it's the post select data, I had to put the code in the queryFn promise.

[TkDodo]

I added console logs to the structuralSharing callback and it appears to only call this function with the post select data.

show a codesandbox reproduction please. I'm pretty sure we first have to call structuralSharing for the data that is returned from the queryFn, so that we get a stable input to select. Then, the result of select is also structurally shared as an optimization.

[TkDodo]

@levidrain any updates please?

[roalonso]

Why was unknown used instead of TQueryFnData | TData? Using unknown forces users to make an extra check to determine which type was passed.

[TkDodo]

because structualSharing runs on query level, and TData is only known on observer level.