Support @GQLValueTypes when rendering API

[jvican]

When using the render method on the GraphQL object, Caliban prints a schema that can be distributed to clients. However, this schema contains no information about value types and instead uses the underlying representation, which loses type information. The GQL Value types could be represented as scalars in the schema, right after the Long and DateTime definitions. I'd like to suggest that Caliban supports this feature either by default, or by opting in via either of the following mechanisms:

1. A configuration option in the render method
2. A GQLScalarType annotation that combines the semantics of GQLValueType and the scalar representation

[ghostdogpr]

The render function is only a reflection of the schema, so in order to change the generated GraphQL type, the Schema must be changed as well (so the type will be consistent in render, in introspection and when validating queries).

You can achieve this today with for example:

case class MyScalar(value: Int)

implicit val myScalarSchema: Schema[Any, MyScalar] = Schema.scalarSchema("MyScalar", None, IntValue(_))

Your second suggestion would work. To prevent breaking existing code, we could re-use GQLValueType but add a parameter isScalar: Boolean = false to turn on this behavior:

@GQLValueType(isScalar = true)
case class MyScalar(value: Int)

Does that sounds like what you wanted?

[ghostdogpr]

Turns out it was simple: #1127

[jvican]

Great! #1127 looks like what I need, thanks for the quick PR and prompt answer. Let me know when this is released as I'll use it right away. Had a brief look at the PR implementation and looks solid, nothing to add.

Your approach to customize the schema instance is something I've considered in the past but it's verbose enough for all my types that I've discarded it, the new solution to this problem is much better.

[ghostdogpr]

@jvican you're lucky, I was about to release so it made it into 1.2.2