retryOnMount as a function (or respect retry function)

[dtaub]

The retry property supports passing a function so that we can determine whether an error is retryable. However, retryOnMount can only be a boolean, which means the only options are to never retry or to always retry, even if the error wasn't retryable in the first place.

2 possible solutions come to mind:

1. Allow retryOnMount to be a function. This would be the most flexible but potentially lead to duplicate logic since probably in 99% of cases we'd want it to be the same logic as retry.
2. Have retryOnMount respect retry and not retry if it returns false. This could be opt-in for backwards compatibility via a type along the lines of boolean | 'auto'.

[TkDodo]

retryOnMount has nothing to do with retry, it’s just a slightly poorly named prop that we mainly use internally to ensure some error boundary / suspense things.

What it does is: if a query is in error state and you mount a new query, do you want to start fetching again or keep showing the error?

This is different from “retry” in the classic react-query sense where a query keeps being in fetchStatus:’fetching’ until all retries have been exhausted and the query finally goes into an error state.

[dtaub]

Fair enough, but the point still stands. Whether I want to refetch on mount could depend what the error is, for similar reasons to `retry`. For instance if it's a 404 and I know refetching won't change that.