Composite computed fields

[asodeur]

Description

This is adding the ability to return non-scalar types from computed fields.

Before this a computed field of non-scalar type would always return null. Now you can do

type S {
   myComputedField: T @computed(selectionSet: "{ fieldA fieldB }")
}

where T is an enum, interface, object, or union type. T does not need to be merged type. However, all types reachable from T will be part of the isolated schema (and potentially the base schema as well).

Related #4554

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Screenshots/Sandbox (if appropriate/relevant):

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How Has This Been Tested?

Unit tests (eventually will need more ...)

Test Environment:

• OS: Windows
• @graphql-tools/stitch: 8.7.47
• NodeJS: 18.15

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests and linter rules pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Further comments

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🦋 Changeset detected

Latest commit: 3669811

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@graphql-tools/stitch	Minor
@graphql-tools/stitching-directives	Patch
federation-benchmark	Patch

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[ardatan]

Thanks for the PR!
Is there anything we can help you to get this finished? @asodeur

[MichalLytek]

@asodeur
Correct me if I'm wrong, but your PR adds the ability to enhance other schema types with computed fields when the return type of the computed field is not scalar but some object type (even local, not stitched)?

Like localDependentField: String! works now but otherTypeField: OtherType! does not and your PR will make it work? 😉

[asodeur]

@MichalLytek yes, that is the plan. As is the PR works in a little in-house PoC but getting all the corner-cases to work required quite some special casing. So there is a lot of clean-up left to do.

[asodeur]

I hope this is ready for a first round of review now. There are some areas that might need better test coverage:

1. I am unsure how this might interact with entry points. Which scenarios, if any, would need to be covered here?
2. do we need to test how circular dependencies among computed fields would behave? Not sure if these can be created in the first place and what would happen.
3. any other omissions in the test coverage?

[ardatan]

How do we expect value here?
Because it is needed for next only, no?

[asodeur]

Yeah, should have made clear by proper typing value is optional and will only be filled if available b/c a) value was explicitly queried, or b) the computed field was queried. Fixed the typing and added a test to show value will not be filled when it is not required.