Add new feature: nullable-result
#1637
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Stacked on #1639
This PR adds a new Cargo feature,
nullable-result.What does it do?
When the feature is enabled, all fields that return
Resultbecome nullable, andnullis returned in place when theResulthasErr().Why do this?
Null bubbling is a nightmare in most cases, which makes nullable-by-default schema one of the best practices for designing GraphQL schemas. However, the existing behavior of
async-graphqldoesn't match with it: error bubbles until it meetsOptionto "capture" it as a null. This makes it too easy to break the app just by not wrapping it withOption, and wrapping all return types from resolvers that returnResultwithOptionis a very tedious, repetitive, and easy-to-miss task to do. This wouldn't have been the case at all ifResultgot resolved into a nullable type.If we also look at the ecosystem, Caliban, a GraphQL server framework for Scala, also infers types of fields from the return type of resolvers and emits nullable types if resolvers return a throwable type like
ZIO[R, Throwable, A](somewhat similar toResult<A, Throwable>.) (ref)While I personally believe that this should be the default for all cases, I guarded it with a Cargo feature for now to keep backward compatibility. I hope we can enable this as default at some point.