Exception thrown when interfaces is null inside an object [0.12.0]

[hlship]

The schema introspection definitions (https://facebook.github.io/graphql/June2018/#sec-Schema-Introspection) indicate that the interfaces field of __Type is a nullable list.

  interfaces: [__Type!]

Our implementation of GraphQL (Lacinia) does, in fact, return a null for objects that do not implement an interface, rather than an empty list.

This results in an exception in the data pane at GraphiQL startup.

Error: Introspection result missing interfaces: {"kind":"OBJECT","name":"QueryRoot","description":"Root of all queries.","fields":[{"name":"hello","description":"Simplest possible query.","args":[],"type":{"kind":"SCALAR","name":"String","ofType":null},"isDeprecated":false,"deprecationReason":null}],"inputFields":null,"interfaces":null,"enumValues":null,"possibleTypes":null}
    at buildObjectDef (http://localhost:8888/assets/graphiql/graphiql.js:33585:13)
    at buildType (http://localhost:8888/assets/graphiql/graphiql.js:33559:18)
    at getNamedType (http://localhost:8888/assets/graphiql/graphiql.js:33524:19)
    at http://localhost:8888/assets/graphiql/graphiql.js:33703:12
    at Array.map (<anonymous>)
    at buildClientSchema (http://localhost:8888/assets/graphiql/graphiql.js:33702:41)
    at http://localhost:8888/assets/graphiql/graphiql.js:2174:55

even though the GraphQL introspection query (here formatted for readability) matches, AFAIK, the introspection schema:

{
    "data": {
        "__schema": {
            "queryType": {
                "name": "QueryRoot"
            },
            "mutationType": null,
            "subscriptionType": {
                "name": "SubscriptionRoot"
            },
            "types": [
                {
                    "kind": "SCALAR",
                    "name": "Boolean",
                    "description": null,
                    "fields": null,
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "SCALAR",
                    "name": "Float",
                    "description": null,
                    "fields": null,
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "SCALAR",
                    "name": "ID",
                    "description": null,
                    "fields": null,
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "SCALAR",
                    "name": "Int",
                    "description": null,
                    "fields": null,
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "OBJECT",
                    "name": "QueryRoot",
                    "description": "Root of all queries.",
                    "fields": [
                        {
                            "name": "hello",
                            "description": "Simplest possible query.",
                            "args": [],
                            "type": {
                                "kind": "SCALAR",
                                "name": "String",
                                "ofType": null
                            },
                            "isDeprecated": false,
                            "deprecationReason": null
                        }
                    ],
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "SCALAR",
                    "name": "String",
                    "description": null,
                    "fields": null,
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "OBJECT",
                    "name": "SubscriptionRoot",
                    "description": "Root of all subscriptions.",
                    "fields": [
                        {
                            "name": "ticks",
                            "description": null,
                            "args": [
                                {
                                    "name": "count",
                                    "description": "Number of ticks to send via subscription.",
                                    "type": {
                                        "kind": "SCALAR",
                                        "name": "Int",
                                        "ofType": null
                                    },
                                    "defaultValue": "5"
                                }
                            ],
                            "type": {
                                "kind": "OBJECT",
                                "name": "tick",
                                "ofType": null
                            },
                            "isDeprecated": false,
                            "deprecationReason": null
                        }
                    ],
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                },
                {
                    "kind": "OBJECT",
                    "name": "tick",
                    "description": "A subscription response.",
                    "fields": [
                        {
                            "name": "count",
                            "description": null,
                            "args": [],
                            "type": {
                                "kind": "SCALAR",
                                "name": "Int",
                                "ofType": null
                            },
                            "isDeprecated": false,
                            "deprecationReason": null
                        },
                        {
                            "name": "time_ms",
                            "description": "Time when tick is emittied (as string-ified long milliseconds since epoch).",
                            "args": [],
                            "type": {
                                "kind": "SCALAR",
                                "name": "String",
                                "ofType": null
                            },
                            "isDeprecated": false,
                            "deprecationReason": null
                        }
                    ],
                    "inputFields": null,
                    "interfaces": null,
                    "enumValues": null,
                    "possibleTypes": null
                }
            ],
            "directives": [
                {
                    "name": "skip",
                    "description": "Skip the selection only when the `if` argument is true.",
                    "locations": [
                        "INLINE_FRAGMENT",
                        "FIELD",
                        "FRAGMENT_SPREAD"
                    ],
                    "args": [
                        {
                            "name": "if",
                            "description": "Triggering argument for skip directive.",
                            "type": {
                                "kind": "NON_NULL",
                                "name": null,
                                "ofType": {
                                    "kind": "SCALAR",
                                    "name": "Boolean",
                                    "ofType": null
                                }
                            },
                            "defaultValue": null
                        }
                    ]
                },
                {
                    "name": "include",
                    "description": "Include the selection only when the `if` argument is true.",
                    "locations": [
                        "INLINE_FRAGMENT",
                        "FIELD",
                        "FRAGMENT_SPREAD"
                    ],
                    "args": [
                        {
                            "name": "if",
                            "description": "Triggering argument for include directive.",
                            "type": {
                                "kind": "NON_NULL",
                                "name": null,
                                "ofType": {
                                    "kind": "SCALAR",
                                    "name": "Boolean",
                                    "ofType": null
                                }
                            },
                            "defaultValue": null
                        }
                    ]
                }
            ]
        }
    }
}

You can see here in the code (buildClientSchema.js.flow, line 213):

  function buildObjectDef(
    objectIntrospection: IntrospectionObjectType,
  ): GraphQLObjectType {
    if (!objectIntrospection.interfaces) {
      throw new Error(
        'Introspection result missing interfaces: ' +
          JSON.stringify(objectIntrospection),
      );
    }
    return new GraphQLObjectType({
      name: objectIntrospection.name,
      description: objectIntrospection.description,
      interfaces: objectIntrospection.interfaces.map(getInterfaceType),
      fields: () => buildFieldDefMap(objectIntrospection),
    });
  }

... there's a check that interfaces are returned ... which is IMO not valid, as interfaces is nullable and a null was returned.

A quick scan of the source code shows that this may apply to possibleTypes, enumValues, inputFields, fields (in __Type) and __Field.args.

By contrast, __Directive.args, which is obviously more recent, was added to the spec as args: [__InputValue!]!.

I'm looking into a workaround where we define these fields as non-null, to force an empty list to be emitted into the response; still either the spec should be updated, or GraphiQL should be updated to match the current spec.

[IvanGoncharov]

The schema introspection definitions (facebook.github.io/graphql/June2018/#sec-Schema-Introspection) indicate that the interfaces field of __Type is a nullable list.

@hlship Right, but the spec has additional constraints based on the value of kind.

interfaces: The set of interfaces that an object implements.

https://facebook.github.io/graphql/June2018/#sec-Object
For all other values of kind it should be null:

All other fields must return null.

https://facebook.github.io/graphql/June2018/#sec-Scalar

That's is why according to the spec interfaces is nullable but should be a list when kind === 'OBJECT' and null in all other cases.

By contrast, __Directive.args, which is obviously more recent, was added to the spec as args: [__InputValue!]!.

Because __Directive doesn't have kind field.

[IvanGoncharov]

@hlship BTW. same principle applies to fields, possibleTypes, enumValues, inputFields.

[hlship]

Interesting; that's easy to miss, as I would have thought that the schema for __Type would have capture it, but in this case, a careful reading of the prose overrides.

Cool enough. I can update Lacinia to match that, I've already done interfaces, but I'll expand to the other mentioned fields.

[IvanGoncharov]

Interesting; that's easy to miss

@hlship Agree 👍 What if we change Introspection SDL like this:

type __Type {
  # ...

  # should be non-null for OBJECT and null for others
  interfaces: [__Type!]
}

What do you think?

[hlship]

That would be helpful for the next person who hits this, I suspect. It's interesting that this is exactly what unions are for, but that would make building and using the introspection schema much more complex.

[IvanGoncharov]

It's interesting that this is exactly what unions are for

@hlship I think the interface would be a better match:

interface __Type {
  description: String
}

type __TypeObject implements __Type {
  description: String
  interfaces: [__TypeInteface!]!
}

Because with unions this query is invalid:

{
  __type(name: "SomeObject") {
    description
  }
}

And you need to have inline fragments for every subtype.

using the introspection schema much more complex.

Not sure about that. Would be interesting to ask Lee about the motivation for this design decision.

[hlship]

Yes, I’m not sure why I thought interface but typed union.

On Wed, Nov 21, 2018 at 4:32 PM Ivan Goncharov ***@***.***> wrote: It's interesting that this is exactly what unions are for I think the interface would be a better match: interface __Type { description: String } type __TypeObject implements __Type { description: String interfaces: [__TypeInteface!]! } Because with unions this query is invalid: { __type(name: "SomeObject") { description } } And you need to have inline fragments for every subtype. using the introspection schema much more complex. Not sure about that. Would be interesting to ask Lee about the motivation for this design decision. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#746 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AADNtLVDRBkvu3ys6PrSwoi5l-c3zmUqks5uxfCXgaJpZM4YsBjH> .

-- Howard M. Lewis Ship Senior Mobile Developer at Walmart Labs (971) 678-5210 http://howardlewisship.com @hlship