mergeSchemas does not report correct NonNullable field errors

[mikebm]

When calling a resolver that returns an item that contains a list, and that list type has a NonNullable field, yet the data getting sent back is null, then the wrong error is reported.

Below is a working example. The error should be reporting URL, but it is reporting quantity instead. It apparently reports the first field no matter what is is.

const { graphql, buildSchema } = require("graphql");
const { mergeSchemas } = require("graphql-tools");

const rootValue = {
  items: [
    { quantity: 1, URL: "Test1" },
    { quantity: 1, URL: "Test2" },
    { quantity: 3, URL: "Test3" },
    { quantity: 3 },
    { quantity: 1, URL: "Test5" }
  ]
};

const schema1 = buildSchema(`
  type Data {
     items: [LineItem]!
  }

  type LineItem {
      quantity: Int!
      URL: String!
  }

  schema { query: Data }
`);

const schema = mergeSchemas({ schemas: [schema1] });

graphql({
  schema,
  source: "{ items { quantity URL } }",
  rootValue
}).then(result => console.log(JSON.stringify(result, null, 2)));

We use mergeSchemas a lot and this error is pretty critical as it causes developers to spend debugging time in the wrong area of the code base.

[yaacovCR]

Should be fixed by #1307, rolling into #1306

[Grmiade]

@yaacovCR It seems this bug is not fixed when I run the @mikebm's example with the new stitchSchemas function (v6.0.9), I have this error:

{
  "errors": [
    {
      "message": "Cannot return null for non-nullable field LineItem.quantity.",
      "locations": [
        {
          "line": 1,
          "column": 11
        }
      ],
      "path": [
        "items",
        3,
        "quantity"
      ]
    }
  ],
  "data": {
    "items": [
      {
        "quantity": 1,
        "URL": "Test1"
      },
      {
        "quantity": 1,
        "URL": "Test2"
      },
      {
        "quantity": 3,
        "URL": "Test3"
      },
      null,
      {
        "quantity": 1,
        "URL": "Test5"
      }
    ]
  }
}

[yaacovCR]

Fixed in v7