Generated code doesn't compile due to missing type conversions

[jonstaryuk]

I'm getting a compiler error when gqlgen creates resolvers based on a field that has a wrapped builtin type. For example:

schema.graphql

schema {
    query: Query
}

type Query {
    foo: Foo
}

type Foo {
    id: String!
}

model.go

package tmp

type Identifier string

type Foo struct {
	ID Identifier
}

types.json

{
    "Foo": "tmp.Foo"
}

$ gqlgen -out gen.go
$ go build
# tmp
./gen.go:84:41: cannot use res (type Identifier) as type string in argument to graphql.MarshalString

Because the generated function uses MarshalString(res) instead of MarshalString(string(res)):

// nolint: gocyclo, errcheck, gas, goconst
func (ec *executionContext) _foo(sel []query.Selection, it *Foo) graphql.Marshaler {
	fields := graphql.CollectFields(ec.doc, sel, fooImplementors, ec.variables)
	out := graphql.NewOrderedMap(len(fields))
	for i, field := range fields {
		out.Keys[i] = field.Alias
		out.Values[i] = graphql.Null

		switch field.Name {
		case "__typename":
			out.Values[i] = graphql.MarshalString("Foo")
		case "id":
			badArgs := false
			if badArgs {
				continue
			}
			res := it.ID

			out.Values[i] = graphql.MarshalString(res) // <-- invalid call
		default:
			panic("unknown field " + strconv.Quote(field.Name))
		}
	}

	return out
}

[vektah]

Interesting, I wasn't expecting it to be used quite like that. It probably should work like that, I'll take a look this afternoon.

In the mean time, you can add the (un)marshalGQL methods to your user type.

eg: https://github.com/vektah/gqlgen/blob/master/example/scalars/model.go#L21-L52

[jonstaryuk]

Ah, I hadn't noticed that workaround before, thanks!