facebook
Refine generated type for assignable fragments on abstract types
Closes #4560
This is quality-of-life change to the type generation for the assignable fragments (aka. typesafe updaters). For the cases where the assignable fragment is defined on the abstract type, and is spread on a concrete implementation of that type. Issue #4560 has a more true-to-life example. But the minimal case is:
type A {}
type B {}
union C = A | B
type Query {
a: A
}
fragment Assignable_c on C @assignable {
__typename
}
fragment Foo on Query {
a {
...Assignable_c
}
}
Same applies to the interfaces as well.
Previously, the generated type for fragment Foo would include __isAssignable_c?: "A" (since the assignable fragment is defined on an abstract type). In some sense, this type is misleading. __isAssignable_c can never be undefined, since A always implements (is member of) abstract type C. This would require writing a gnarly validator. The validator turns out to be redundant in the end, and is just there to satisfy the type system.
This is a small patch that checks if the abstract type spread is done on the concrete subtype of the supertype (ie. fragment of union C is spread its member A). If the check is successful, the optionality of __isAssignable_c?: "A" is removed. This is a safe assumption, since the only way for A not to be a subtype of C:
- is to it remove
Aas a member of unionC(if C is a union) - or to remove conformance of
Ato the interfaceC(if C is an interface)
Both of which are breaking schema changes anyhow.
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