`DefaultResolveFn` does not work as expected with `map[K]V` for `K` that has string as the underlying type

[bkrukowski]

Issue

DefaultResolveFn works properly for the following maps:

type MyMap map[string]any

but when we change the map key:

type MyKey string

type MyMap map[MyKey]any

it returns the following errors:

reflect.Value.MapIndex: value of type string is not assignable to type .*

Example:

Error

2009/11/10 23:00:00 failed to execute graphql operation, errors: [reflect.Value.MapIndex: value of type string is not assignable to type main.TranslationKey reflect.Value.MapIndex: value of type string is not assignable to type main.TranslationKey]

Code

package main

import (
	"encoding/json"
	"fmt"
	"log"

	"github.com/graphql-go/graphql"
)

type TranslationKey string

type Translation map[TranslationKey]string

func main() {
	// Schema
	fields := graphql.Fields{
		"hello": &graphql.Field{
			Type: graphql.NewObject(graphql.ObjectConfig{
				Name: "Translation",
				Fields: graphql.Fields{
					"en": &graphql.Field{
						Type: graphql.String,
					},
					"fr": &graphql.Field{
						Type: graphql.String,
					},
				},
			}),
			Resolve: func(p graphql.ResolveParams) (interface{}, error) {
				return Translation{
					"en": "hello",
					"fr": "bonjour",
				}, nil
			},
		},
	}
	rootQuery := graphql.ObjectConfig{Name: "RootQuery", Fields: fields}
	schemaConfig := graphql.SchemaConfig{Query: graphql.NewObject(rootQuery)}
	schema, err := graphql.NewSchema(schemaConfig)
	if err != nil {
		log.Fatalf("failed to create new schema, error: %v", err)
	}

	// Query
	query := `
		{
			hello {
				en
				fr
			}
		}
	`
	params := graphql.Params{Schema: schema, RequestString: query}
	r := graphql.Do(params)
	if len(r.Errors) > 0 {
		log.Fatalf("failed to execute graphql operation, errors: %+v", r.Errors)
	}
	rJSON, _ := json.Marshal(r)
	fmt.Printf("%s \n", rJSON)
}

https://go.dev/play/p/giPGGUxKht8

Solution

The following PR solves that problem, but I believe it's been wrongly closed.

#697

Please take a look at the deeper explanation in the comment #697 (comment)

[bkrukowski]

@chris-ramon I hope this description clarifies your doubts

[chris-ramon]

ok thanks for the details, I'll give it a look.

[git-hulk]

@chris-ramon Would you mind having a look at PR #704