Scala `Seq` is not recognised as list

[Mikołaj Walczak]

Description

After switching code generation from Java to Scala schema parser build fails with the following exception:

java.lang.ClassCastException: class graphql.kickstart.tools.util.ParameterizedTypeImpl cannot be cast to class java.lang.Class

It seemed caused by isListType inside TypeClassMatcher only checking for java.lang.Iterable causing scala Seq to not be considered a list type.

Expected behavior

SchemaParser build returns parses the schema properly.

Actual behavior

SchemaParser build throws java.lang.ClassCastException.

Steps to reproduce the bug

Given example schema

# schema.graphqls
query {
  topics(prefix: String!): [Topic!]!
}

type Topic {
  topic: String!
}

Scala classes autogenerated with: https://github.com/kobylynskyi/graphql-java-codegen

// Topic.scala
case class Topic(topic: String)

// QueryResolver.scala
trait QueryResolver extends graphql.kickstart.tools.GraphQLQueryResolver {
  def topics(prefix: String): java.util.concurrent.CompletionStage[scala.Seq[Topic]]
}

Actual query resolver implementation

// QueryResolverImpl.scala
class QueryResolverImpl extends QueryResolver {
  override def topics(prefix: String): java.util.concurrent.CompletionStage[scala.Seq[Topic]] = ???
}

Trying to build schema will fail with an exception

object Test extends App {
  val schema = SchemaParser.newParser()
    .files("schema.graphqls")
    .resolvers(new QueryResolverImpl())
    .build()
    .makeExecutableSchema()
}

[Oryan]

I don't believe we generally support Scala.
Is this the only obstacle?

[Oryan]

Closing for now.