codegen: executableSchema schema configurable

codegen/generated!.gotpl

@@ -18,13 +18,15 @@
 	// NewExecutableSchema creates an ExecutableSchema from the ResolverRoot interface.
 	func NewExecutableSchema(cfg Config) graphql.ExecutableSchema {
 		return &executableSchema{
+		 	schema: cfg.Schema,
 			resolvers: cfg.Resolvers,
 			directives: cfg.Directives,
 			complexity: cfg.Complexity,
 		}
 	}
 
 	type Config struct {
+		Schema    *ast.Schema
 		Resolvers  ResolverRoot
 		Directives DirectiveRoot
 		Complexity ComplexityRoot
@@ -93,12 +95,16 @@
 
 {{ if eq .Config.Exec.Layout "single-file" }}
 	type executableSchema struct {
+		schema    *ast.Schema
 		resolvers  ResolverRoot
 		directives DirectiveRoot
 		complexity ComplexityRoot
 	}
 
 	func (e *executableSchema) Schema() *ast.Schema {
+		if e.schema != nil {
+        		return e.schema
+		}
 		return parsedSchema
 	}