total rewrite to interface handling; not complete but it compiles

generate/testdata/QueryWithAlias.graphql.go

@@ -1,5 +1,29 @@
-type Response struct {
-	User *struct {
-		ID string
+package test
+
+// Code generated by github.com/Khan/genql, DO NOT EDIT.
+
+import (
+	"context"
+
+	"github.com/Khan/genql/graphql"
+)
+
+type QueryWithAliasResponse struct {
+	User *User
+}
+
+type User struct {
+	ID string
+}
+
+func QueryWithAlias(client *graphql.Client) (*QueryWithAliasResponse, error) {
+	var retval QueryWithAliasResponse
+	err := client.MakeRequest(context.Background(), `
+query QueryWithAlias {
+	User: user {
+		ID: id
 	}
 }
+`, &retval, nil)
+	return &retval, err
+}