Fix usePermissions always triggers a re-render even though the permissions are unchanged

[fzaninotto]

Problem

All react-admin routes (list, edit, create, etc) are wrapped by WithPermissions. This component renders the page content optimistically with empty permissions, then calls authProvider.getPermissions(), and passes the result to the child.

In many cases, this means the routes will render twice: once with empty permissions, and once with the permissions returned by the authProvider.

Solution

WithPermissions calls authProvider.getPermissions() with empty params. In many cases, the result of this call is always the same.

useGetPermissions can cache the result from the first call, and initialize its state with it.

that way, in most cases, the return from authProvider.getPermissions() will be the same as the cached one, and we'll save a re-render.

This should git a short perf boost to all apps, whether they use permissions or not.

Before

12 renders when coming back to the Post List page

After

11 renders when coming back to the Post List page

[fzaninotto]

That won't work because even though the permissions don't change, usePermissions changes the loading state once auth.getPermissions() returns, and that triggers a rerender.

This is unfortunate here as we don't use the loading state.

this means we must introduce a new hook that only stores the permissions, but not the loading state.

[djhi]

I can't figure a better name but I'm not convinced by usePermissionsOptimized. I think most people will end up using it just because of the name even though they need its loading state

[djhi]

Oh and you forgot to document it ;)

[fzaninotto]

It's an internal API. I'm not even sure we should export it.