Support multiple resolvers on fields

[tusharmath]

Currently, only one resolver at a time is supported on a field. We want to change it to allow multiple resolvers:

DSL Changes

type Query {
  data: Data
    @http(url: "http://api.com/foo")
    @http(url: "http://api.com/bar")

  dataList: [Data]
    @http(url: "http://api.com/foo")
    @http(url: "http://api.com/bar")
}

Runtime Changes

• Given multiple resolvers (HTTP gRPC or GraphQL) the expectation is to perform deep merge as follows by creating a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:

  1. and both values are objects, the two values will be recursively merged
  2. otherwise if the value is an array, the two values should be concatenated
  3. otherwise the value from the second object will be used.

• Note the select operation should be applied first on the HTTP and only then should it be picked up for merging.

Technical Requirements

• Add unit tests for this deep merge algorithm
• Add integration tests to check end to end execution flow is implemented correctly.