Impl seems to be not aligned with the section Errors and Non-Nullability of the spec

[shafreenAnfar]

Version: Beta2

Spec says the below,

"If an error is thrown while resolving a field, it should be treated as though the field returned null, and an error must be added to the "errors" list in the response."

but our implementation seems to be a bit different.

Consider the below apollo example, query and the expected behaviour.

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

const typeDefs = gql`
  type Book {
    title: String
    author: String
  }

  type Query {
    books: [Book]
  }
`;

const books = [
  {
    title: 'The Awakening',
    author: new Error("Could not finnd author"),
  },
  {
    title: 'City of Glass',
    author: 'Paul Auster',
  },
];

const resolvers = {
  Query: {
    books: () => books,
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

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

Query

{
  books {
    title
    author
  }
}

Expected result

{
  "errors": [
    {
      "message": "Could not finnd author",
      "locations": [
        {
          "line": 4,
          "column": 5
        }
      ],
      "path": [
        "books",
        0,
        "author"
      ],
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR",
        "exception": {
          "stacktrace": [
            "Error: Could not finnd author",
            "    at Object.<anonymous> (/Users/shafreen/Documents/pcm/graphql/appollo/graphql-server-example/index.js:17:13)",
            "    at Module._compile (node:internal/modules/cjs/loader:1101:14)",
            "    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)",
            "    at Module.load (node:internal/modules/cjs/loader:981:32)",
            "    at Function.Module._load (node:internal/modules/cjs/loader:822:12)",
            "    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:79:12)",
            "    at node:internal/main/run_main_module:17:47"
          ]
        }
      }
    }
  ],
  "data": {
    "books": [
      {
        "title": "The Awakening",
        "author": null
      },
      {
        "title": "City of Glass",
        "author": "Paul Auster"
      }
    ]
  }
}

Note: "author": null

Now consider the same program in Ballerina,

import ballerina/graphql;

service / on new graphql:Listener(4000) {

    resource function get books() returns Book[]? {

        return [new Book("The Awakening", error("Could not finnd author")), new Book("City of Glass", "Paul Auster")];
    }
}

service class Book {

    private string title;
    private string|error author;

    public function init(string title, string|error author) {
        self.title = title;
        self.author = author;
    }

    resource function get title() returns string? {
        return self.title;
    }
    resource function get author() returns string|error? {
        return self.author;
    }
}

and the response

{
  "errors": [
    {
      "message": "Could not finnd author",
      "locations": [
        {
          "line": 4,
          "column": 5
        }
      ],
      "path": [
        "books",
        0,
        "author"
      ]
    }
  ],
  "data": {
    "books": [
      {
        "title": "The Awakening"
      },
      {
        "title": "City of Glass",
        "author": "Paul Auster"
      }
    ]
  }
}

Note: missing author attribute, ideally it should be there with null value.