Cache Gathered Selections

[rmosolgo]

When a fragment is spread on a list of items, we re-call gather_selections(...) for each item on the list, and that can get really slow.

I'm trying to find a reusable data structure which will reduce the work in that case without slowing down the common case.

I tried this before and it caused an infinite loop -- repeatedly running the same fields -- so I'm going to take it slower and write unit tests for it.

TODO:

• Make the new system opt-in
• Pass CI with it turned on for some builds
• Ensure that the benchmark improves runtime and memory

[rmosolgo]

The main challenge here is handling the fact that there's a split in what can be done when:

• Ahead-of-time:
  • can gather up selections by name
  • can enter into untyped inline fragments (... { ... })
  • can't enter into typed inline fragments or into fragment spreads, because you can't check the current (runtime) type
    • TODO: if the fragment's type matches the type which owns the selection, can you continue without performing any checks?
  • can't resolve directives because you don't have the object
• Running the query:
  • can check the runtime type of the object against the static type condition of a fragment, optionally continuing
  • can evaluate directives, since the runtime object is present
    • TODO handle @skip and @include specially, since they don't need the object?

So you end up needing a creating of bookkeeping objects ahead-of-time so that, at runtime, you can check the various conditions (types, directives) and optionally continue exection.

TODO maybe a hybrid approach would work, where it tries to use a a cached selection, and it does, if there aren't any conditions that require runtime work, but if there's a type condition or directive, it fails back to runtime gathering (the current implementation).