Object given to custom scalar serialize changes type

[moret]

Hi! I've tried merging existing schemas which use graphql-custom-datetype as a custom scalar type. The merged schema however is turning the original resolved value at some point to a string - I could not figure out where - resulting in a serialization error on the custom scalar code. These are the steps to reproduce and what I expected to happen - although to be clear I'm not really familiar with custom scalar resolving, so I'm not sure if the resolved value should really be kept all the way until it's serialized or if it's expected to be changed at some point.

Steps to reproduce:
Run one of the following examples:

• Apollo Launchpad example
• Code on Node.js:

const {
  graphql,
  GraphQLObjectType,
  GraphQLSchema,
} = require('graphql');
const { mergeSchemas } = require('graphql-tools');
const CustomGraphQLDateType = require('graphql-custom-datetype');

const now = new Date();

const clockSchema = new GraphQLSchema({
  query: new GraphQLObjectType({
    name: 'clock',
    fields: {
      now: {
        resolve: () => now,
        type: CustomGraphQLDateType,
      }
    },
  })
});

graphql(
  clockSchema,
  '{ now }'
).then(result => {
  console.assert(
    result.data.now == now.toISOString(),
    'clock schema out of sync with the now'
  );
}).catch(e => {
  console.log(e);
});

const theGrandSchema = mergeSchemas({
  schemas: [clockSchema],
});

graphql(
  theGrandSchema,
  '{ now }'
).then(result => {
  console.log(result);
  console.assert(
    result.data.now == now.toISOString(),
    'the grand schema out of sync with the now'
  );
}).catch(e => {
  console.log(e);
});

Expected behaviour:
Queries on now to return an ISO timestamp - ex.: "2017-10-26T15:35:53.292Z".

Actual behaviour
Queries on now throw a TypeError: Field error: value is not an instance of Date from the custom scalar serialization because it gets a string instead of a Date.

[yaacovCR]

This should be fixed by #1307 see https://runkit.com/yaacovcr/custom-scalars

[yaacovCR]

Consolidating into #1306 .