Cannot use global mutate with useSWRInfinite

Bug report

Description / Observed Behavior

There is no way to mutate data fetched with useSWRInfinite without first fetching the data client-side. I saw this answer by @shuding and it definitely works, but it triggers a fetch when all I want to do is mutate data (if it has already been fetched).

Expected Behavior

Instead, I should be able to mutate local data without triggering a fetch. The global mutate function should allow me to mutate data that has already been fetched (e.g. on a page that uses useSWRInfinite) on a page that should not trigger a fetch of that data.

My (pretty common I think) use-case:

1. I have a list of emails fetched using useSWRInfinite on a /feed page.
2. When the user opens an email, they can modify it on a /messages/[id] page.
3. I want to mutate the data shown on the /feed page when the data is edited on the /messages/[id] page.

But, the user can also open the /messages/[id] page directly, in which case the /feed page will never have been opened and useSWRInfinite will never have been called. In this case, I don’t want to trigger a fetch with useSWRInfinite.

Repro Steps / Code Example

This is the project I’m working on: nicholaschiang/hammock.

Additional Context

SWR version: 0.5.5 Related to #435.

[shuding]

I’m not sure if it’s a good idea to expose internal implementation details (things like inf), as they will likely to change over time. The idea of #1174 is to support use cases like mutate(regex) or mutate(filterFn) in the future.

While useSWRInfinite is a truly special case, I’d propose a mutateInfinite method so you can do mutateInfinite(KEY_FOR_FIRST_PAGE) or mutateInfinite(getKey). It basically hides the inf inside.

[koba04]

A solution in https://github.com/vercel/swr/issues/1156#issuecomment-845264050 might work at this time, but it would be broken in the future. For example, https://github.com/vercel/swr/pull/1174 breaks your solution. I think SWR should provide a solution to generate the key, which doesn’t depend on the internal implementation if there is any valid use-case that the global mutate has to use.