Schema missing custom directives when using loadSchemaSync

[z-zainuddin]

When using loadSchemaSync to load a schema file, custom directives are missing from loadSchemaSync output schema.

Given the following schema.gql file, default deprecated directive and custom upper are defined in the schema.

directive @upper on FIELD_DEFINITION

type Profile {
  name: String @deprecated
  fullname: String @upper
}

type Query {
  profile: Profile
}

However, the schema output from loadSchemaSync only contain the deprecated directive but missing the upper directive as follows.

directive @upper on FIELD_DEFINITION

type Profile {
  name: String @deprecated
  fullname: String
}

type Query {
  profile: Profile
}

Here is the loadSchemaSync code.

const schema = loadSchemaSync(`${__dirname}/schema.gql`, {
  loaders: [
    new GraphQLFileLoader(),
  ],
});

What could be the issue here?