Ben Kraft
520532eb65
I didn't realize until today that implementations of GraphQL interfaces are actually allowed to be covariant: if the interface has a field `f: T`, then the implementations may have fields `f: U` where `U` is a subtype of `T` (for example `U` may be an implementation of the interface `T`, or `U` may be `T!` if `T` is non-nullable. (I thought it had to be `f: T` exactly.) So I figured I'd add a test and see what breaks. Surprisingly, and despite the fact that Go interfaces do *not* allow covariance, everything... worked? There's at least one place where it's possible we could ideally use a more specific type [1], but for now I just wanted to make sure we at least write something that builds and is vaguely reasonable. Of course I'm not sure if there's anything I've missed (some day I need to find a fuzzing engine that can fuzz GraphQL). [1] Specifically, the field `CovariantInterfaceImplementationRandomItemTopic.Next` might ideally have type `...NextContentTopic`, not `...NextContent`; we know it's a topic. This doesn't directly cause covariance problems in Go: the method `GetNext` still returns `...NextContent` so the interface matches. But that trick doesn't work for the sibling field `.Related` which is slice-typed: or rather, we'd need the method to copy the slice to the correct type. (Not to mention the implemention of any change here would require a bunch of plumbing because the AST doesn't quite have what we want.) So it's probably best to just keep this as-is for simplicity and consistency. Test plan: make check
10 lines
771 B
JSON
10 lines
771 B
JSON
{
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"operations": [
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{
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"operationName": "CovariantInterfaceImplementation",
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"query": "\nquery CovariantInterfaceImplementation {\n\trandomItem {\n\t\t__typename\n\t\tid\n\t\tnext {\n\t\t\t__typename\n\t\t\t... ContentFields\n\t\t}\n\t\trelated {\n\t\t\t__typename\n\t\t\t... ContentFields\n\t\t}\n\t}\n\troot {\n\t\t... ContentFields\n\t\t... TopicFields\n\t\tnext {\n\t\t\t... TopicFields\n\t\t}\n\t\trelated {\n\t\t\t... TopicFields\n\t\t}\n\t}\n}\nfragment ContentFields on Content {\n\tnext {\n\t\t__typename\n\t\tid\n\t}\n\trelated {\n\t\t__typename\n\t\tid\n\t}\n}\nfragment TopicFields on Topic {\n\tnext {\n\t\tid\n\t}\n\trelated {\n\t\tid\n\t}\n}\n",
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"sourceLocation": "testdata/queries/CovariantInterfaceImplementation.graphql"
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}
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]
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}
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