Accepting value Json in parameter of request's body in custom Scalar

example/scalar_map/server.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	graphql "github.com/graph-gophers/graphql-go"
+	"github.com/graph-gophers/graphql-go/example/scalar_map/types"
+	"github.com/graph-gophers/graphql-go/relay"
+)
+
+
+type Args struct {
+	Name string
+	Data types.Map
+}
+
+
+type mutation struct{}
+
+func (_ *mutation) Hello(args Args) string { 
+
+	fmt.Println(args)
+
+	return "Args accept!"
+}
+
+func main() {
+	s := `
+		scalar Map
+
+		type Query {}
+
+		type Mutation {
+			hello(
+				name: String!
+				data: Map!
+			): String!
+		}
+	`
+	schema := graphql.MustParseSchema(s, &mutation{})
+	http.Handle("/query", &relay.Handler{Schema: schema})
+
+	log.Println("Listen in port :8080")
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

example/scalar_map/types/map.go

@@ -0,0 +1,19 @@
+package types
+
+import "fmt"
+
+type Map map[string]interface {}
+
+func (Map) ImplementsGraphQLType(name string) bool {
+	return name == "Map" 
+}
+
+func (j *Map) UnmarshalGraphQL(input interface{}) error {
+	json, ok := input.(map[string]interface{})
+	if !ok {
+		return fmt.Errorf("wrong type")
+	}
+
+	*j = json
+	return nil
+}

internal/validation/validation.go

@@ -778,7 +778,9 @@ func validateValueType(c *opContext, v types.Value, t types.Type) (bool, string)
 			if validateBasicLit(lit, t) {
 				return true, ""
 			}
+			return false, fmt.Sprintf("Expected type %q, found %s.", t, v)
 		}
+		return true, ""
 
 	case *types.List:
 		list, ok := v.(*types.ListValue)