- delegateToSchema stores a Receiver object within any returned ExternalObject. The Receiver manages the incoming AsyncIterable payloads and any requests for as yet unretrieved data.

- use new type merging algorithm that lazily merges fields from additional subschemas as needed at field resolution time.

- add __typename to all selection sets, but only once, needed because any type with deferred fields requires __typename

Just a types update

Precompile selection set hints into arrays of field nodes

Dynamic selectionSet hints therefore now return an array of field nodes instead of a selectionSet!

…added later

…so that wrapSchema can be aware of the transformedSchema

stitchSchemas was previously aware of this via StitchingInfo

now that it is added everywhere

…ng data from it

not sure why (yet?), but it also helps some tests pass

 Implementation adapted from: repeaterjs/repeater#48 (comment) so that all payloads will be delivered in the original order

for consistency

WIP, now emits results with merged errors, plan to emit plain results

goal: create receivers that can be more easily modified for batching

change resolveExternalValue => createExternalValue

… rather than annotating

this removes this logic from the receiver, which will help receiver proxying

…es, this allows the merged results to be agnostic of stitched base paths, and enables implementing batching of merged results irrespective of possible changes to the base paths

to make some better magic

by splitting prior to externalValue creation we will be able to use the correct info

We may end up having one type of Receiver
Receivers can also return external values not just MergedExecutionResults, even if the cache is of MergedExecutionsResults

repeaterjs/repeater#48 (comment)

add additional tests

It can be passed a stream of transformedResults using mapAsyncIterator

note that using `break` in for await(...of...) causes abrupt completion and will return the iterator, not really sure why this became a problem only when mapping the iterator

...to use DataLoader for the actual GraphQL results, rather than the external values

This allows us to properly transduce streams.

TODO:
1. We should now be able to add the stream directive for batchDelegateToSchema.
2. Refactor error parsing, now we are relying on the onLocatedError option, but this
   is no longer necessary. Note that additional tests for batched errors are now passing
   (see #2951)
3. Bring back createBatchDelegateFn, that may be useful
4. The Receiver is now created separately for each list item, which means that the
   initialPathDepth probably does not match? This will require a separate argument to
   the Receiver constructor for adjustment
5. Bring back valuesFromResults and fix documentation, we now operate on GraphQL
   results, so should be fewer pitfalls (see #2829)

try to avoid breaking changes (in the future?)