Query Parameter for List of Union

Library Version

GraphQL Kotlin Spring Server - 3.1.0

Describe the bug

A query parameter of type List of a Union type generates a “valid” schema (see SDL below). However the only valid GraphQL query is the following:

{
  shapes(colors:[]) {
    id
  }
}

and attempting to put any object into colors: [] fails with “Validation error of type WrongType”.

To Reproduce

@SpringBootApplication
class Application

fun main(args: Array<String>) {
    runApplication<Application>(*args)
}

@Component
class ShapesQuery : Query {
    suspend fun shapes(colors: List<Colors>): List<Shape> = listOf()
}

data class Shape(val id: String)

interface Colors

data class Red(val red: String): Colors
data class Blue(val blue: String): Colors

• Visit Playground and query for shapes.

Expected behavior

It should probably be invalidated at startup as it would appear Unions on input types are not supported in the GraphQL spec (currently?).

Generated SDL

schema {
  query: Query
}

"Directs the executor to include this field or fragment only when the `if` argument is true"
directive @include(
    "Included when true."
    if: Boolean!
  ) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT

"Directs the executor to skip this field or fragment when the `if`'argument is true."
directive @skip(
    "Skipped when true."
    if: Boolean!
  ) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT

"Marks the field or enum value as deprecated"
directive @deprecated(
    "The reason for the deprecation"
    reason: String = "No longer supported"
  ) on FIELD_DEFINITION | ENUM_VALUE

"Exposes a URL that specifies the behaviour of this scalar."
directive @specifiedBy(
    "The URL that specifies the behaviour of this scalar."
    url: String!
  ) on SCALAR

union Colors = Blue | Red

type Blue {
  blue: String!
}

type Query {
  shapes(colors: [Colors!]!): [Shape!]!
}

type Red {
  red: String!
}

type Shape {
  id: String!
}

[dariuszkuc]

I believe the problem is here -> https://github.com/ExpediaGroup/graphql-kotlin/blob/master/graphql-kotlin-schema-generator/src/main/kotlin/com/expediagroup/graphql/generator/types/generateArgument.kt#L32

if (parameter.isInterface() && parameter.isList().not()) {
  throw InvalidInputFieldTypeException(parameter)
}

i.e. we check whether parameter is an interface AND is not a list (as list is an interface), proper check should unwrap the type and then validate it -> something along those lines

val parameterType = if (parameter.isList()) {
  parameter.type.getWrappedType()
} else {
  parameter.type
}
if (parameterType.getKClass().isInterface()) {
  throw InvalidInputFieldTypeException(parameter)
}

I’ll submit a patch tomorrow.

[dariuszkuc]

I agree schema generation should fail in this scenario.