JSON Unmarshall change in 0.17.71

[rmillet-rs]

Hello,

there was a change in 0.17.71 (probably "json.Marshaler to Enum code gen by @sonatard in #3663") that introduce a bug in my app.

Reproduction:

GraphQL schema:

enum MyEnum {
    VAL0
    VAL1
    VAL2
}

type MyObj {
    thing1: String!
    thing2: MyEnum!
    thing3: String!
}

input MyObjInput {
    thing1: String
    thing2: MyEnum
}

extend type Mutation{
    myMutation(obj: MyObjInput!): MyObj!
}

And the resolver:

func (r *mutationResolver) MyMutation(ctx context.Context, obj MyObjInput) (*MyObj, error) {
	var ret MyObj

	bytes, err := json.Marshal(obj)
	if err != nil {
		return nil, err
	}

	err = json.Unmarshal(bytes, &ret)
	if err != nil {
		return nil, err
	}

	ret.Thing3 = "ok"

	return &ret, nil
}

The request:

query:

mutation MyMutation($obj: MyObjInput!) {
  myMutation(obj: $obj) {
    thing1
    thing2
    thing3
  }
}

args:

{
    "obj": {
      "thing1": "test"
    }
}

In v0.17.70, the response:

{
  "data": {
    "myMutation": {
      "thing1": "test",
      "thing2": "",
      "thing3": "ok"
    }
  }
}

In v0.17.73, the response (I have a custom error handler):

{
  "errors": [
    {
      "message": "internal error",
      "extensions": {
        "code": "UNKNOWN"
      }
    }
  ],
  "data": null
}

This is due to the strconv.Unquote in MyEnum.UnmarshalJSON where the value is null (without quotes) so it throws "invalid syntax".

Because I have nullable_input_omittable: true, I used the conversion to JSON to ease working with Omittable.

So I wonder if:

• it is a bug in the UnmarshalJSON function?
• should use something else instead?
• should refactor my code to change how I fill the output structure?

Thank you

[sonatard]

Thank you for your report.

I wrote minimal code to reproduce the issue.
The input is Optional, but the return value is not. Therefore, it feels like the correct behavior for an error to occur when trying to unmarshal null into a non-Optional field.
https://go.dev/play/p/9WRLb5495cZ

The issue can be resolved by making the return value's field Optional, as shown below.
https://go.dev/play/p/Oc2r0DoiTYU

[rmillet-rs]

Thank you, I will update my code.