Error when performing queries with variable inside array literal

When running a query with variables inside array literal, an error Variable "$varName" is not defined by operation "Query_fieldName".. For example,

# With this schema
extend type Query {
  searchUsers (ids: [ID!]!): [User]
}

# The following query fails
query search($userId: ID!) {
  searchUsers(ids: [$userId]) {
    id
  }
}

Operations like these work on Apollo Server. When I added a similar query into the base mercurius repo's tests, it also passes. Only in mercurius-gateway it fails.

The following test fails.

test('It support variable inside array literal', async t => {
  const users = [{
    id: 'u1',
    name: {
      firstName: 'John',
      lastName: 'Doe'
    }
  }, {
    id: 'u2',
    name: {
      firstName: 'Jane',
      lastName: 'Doe'
    }
  }]

  const [userService, userServicePort] = await createService(
    t,
    `
    directive @customDirective on FIELD_DEFINITION

    extend type Query {
      searchUsers (ids: [ID!]!): [User]
    }

    type User @key(fields: "id") {
      id: ID!
      name: UserName!
    }

    type UserName {
      firstName: String!
      lastName: String!
    }
  `,
    {
      Query: {
        searchUsers: (root, args) => {
          return users.filter((u) => args.ids.includes(u.id))
        }
      }
    }
  )

  const gateway = Fastify()
  t.teardown(async () => {
    await gateway.close()
    await userService.close()
  })

  await gateway.register(plugin, {
    gateway: {
      services: [
        {
          name: 'user',
          url: `http://localhost:${userServicePort}/graphql`
        }
      ]
    }
  })

  const query = `
  query MainQuery(
    $userId: ID!
  ){
    searchUsers (ids: [$userId]) {
      id
      name {
        firstName
        lastName
      }
    }
  }`

  const res = await gateway.inject({
    method: 'POST',
    headers: {
      'content-type': 'application/json'
    },
    url: '/graphql',
    body: JSON.stringify({
      query,
      variables: {
        userId: 'u1'
      }
    })
  })

  t.same(JSON.parse(res.body), {
    data: {
      searchUsers: [users[0]]
    }
  })
})

mercurius-js / mercurius-gateway

Error when performing queries with variable inside array literal #95