[epic] Inlined client pointers

[rbalicki2]

• Client pointers by default create a follow up request, e.g.

iso(`
  pointer User.bestFriend to User {
    friends { id, closeness }
  }
`)(({ data }) => returnIdOfFriendWithMaxCloseness(data.friends))

iso(`
  field User.SomeField {
    bestFriend { name }
  }
`)(...)

would result in the parent query containing friends { id, closeness } and another request for node(id: $bestFriendId) { ... on User { name } }.

• Instead, we should allow users to inline the selections of the client pointer into the parent field, e.g. in the above case issuing the query friends { id, closeness, name } (i.e. overfetching)

Other tasks

• sub task refetch fields should be optional: The original assumption (by bad!) was that the refetch field would not be optional, because a client pointer will always result in a follow-up request. But that's not true! We can inline the client pointer results in the parent query, and avoid a follow up request. At this point, we don't need a refetch strategy. So, the task is to make the refetch field optional. This can be done as part of the work to support inlining.

[PatrykWalach]

How do we know where to inline the fields?

[rbalicki2]

Not sure. Directive in SomeField, I would think.

[PatrykWalach]

There should be one in bestFriend on friends to mark the spot, then another in SomeField to opt into in-lining?

[rbalicki2]

Great point. Yes you're right.

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This works well with the project to make the parameter type of the pointer generic, in order to force you to return an ID you received from the parameter.

ie BestFriendPointer and expect a return value of T, and have all the potential target IDs be replaced with T (or links?)

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Of course one should be able to not inline and thus return an arbitrary link, e.g. one stored in local state, in which case the parameter can't be generic

[rbalicki2]

Actually one should be able to do both for the same pointer, so I guess the return type can be T (only inline), T |Link<User> (both) or Link (only external or never inlined)

We can probably do some cool stuff at runtime, like tagging the Link with an additional prop or putting it in a set, in order to warn if the user returns a Link from the parameter without indicating it could be inlined