apollo-server: Custom scalars don't run when using modules

Hi! We are using Apollo Server modules to organize our code at OkCupid, and as I looked into adding custom scalars to our graph, it appears that they don’t quite work with modules.

I took this example from the Apollo Server docs, added a few console logs, and updated it to pass the typeDefs and resolvers in as a module instead of on the top level.

const { ApolloServer, gql } = require('apollo-server');
const { GraphQLScalarType, Kind } = require('graphql');

const myCustomScalarType = new GraphQLScalarType({
  name: 'MyCustomScalar',
  description: 'Description of my custom scalar type',
  serialize(value) {
    console.log("serialize");
    let result;
    // Implement custom behavior by setting the 'result' variable
    return result;
  },
  parseValue(value) {
    console.log("parse");
    let result;
    // Implement custom behavior here by setting the 'result' variable
    return result;
  },
  parseLiteral(ast) {
    console.log("literal");
    switch (ast.kind) {
      case Kind.Int:
      // return a literal value, such as 1 or 'static string'
    }
  }
});

const schemaString = gql`
  scalar MyCustomScalar

  type Foo {
    aField: MyCustomScalar
  }

  type Query {
    foo: Foo
  }
`;

const resolverFunctions = {
  MyCustomScalar: myCustomScalarType,
  Query: {
    foo: () => {
      return { aField: 1 };
    },
  },
};

const scalarModule = {
  typeDefs: schemaString,
  resolvers: resolverFunctions,
};

const server = new ApolloServer({
  modules: [ scalarModule ],
});

server.listen().then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`)
});

I expect the docs to reflect the new type, and for the serialize log on line 8 to run when a request is made in playground. But while I see the the MyCustomScalar type details, the description doesn’t come through. And when I execute a request, none of the myCustomScalarType functions run.

Thanks in advance for your time, and thanks for making a great tool! Please let me know if there’s anything else I can provide to help debug this. I’m also quite new to GraphQL, so let me know if I’ve misunderstood something here!