Introspection example to resolve GraphQL schema stitching error swallowing.

introspection.ts

import fetch from "cross-fetch";
import {
	makeRemoteExecutableSchema,
	introspectSchema,
	mergeSchemas
} from "graphql-tools";
import { createHttpLink } from "apollo-link-http";
import { onError } from "apollo-link-error";
import { GraphQLSchema, GraphQLError } from "graphql";

const errorLink = onError(args => {
	if (args.graphQLErrors && args.graphQLErrors.length === 1) {
		args.response.errors = args.graphQLErrors.concat(new GraphQLError(""));
	}
});

export class Introspection {
	public static async getRootSchema(endpoints: string[]) {
		return mergeSchemas({
			schemas: await Promise.all(endpoints.map(this.getIntrospectSchema))
		});
	}

	public static async getIntrospectSchema(
		url: string
	): Promise<GraphQLSchema> {
		// Create a link to a GraphQL instance by passing fetch instance and url
		const makeServiceLink = () =>
			createHttpLink({
				uri: url,
				fetch
			});

		// Fetch our schema
		const serviceSchemaDefinition = await introspectSchema(
			makeServiceLink()
		);

		// make an executable schema
		return makeRemoteExecutableSchema({
			schema: serviceSchemaDefinition,
			link: errorLink.concat(makeServiceLink())
		});
	}
}