no-pageconfig-base-url

Disallow calling PageConfig.getBaseUrl() outside of makeSettings().

Why

JupyterLab supports swapping the backend URL at runtime via a custom ServiceManagerPlugin<ServerConnection.ISettings>. This only works when code retrieves baseUrl fresh from a stored ServerConnection.ISettings object each time it is needed, rather than capturing it once at construction time.

Calling PageConfig.getBaseUrl() directly bypasses ServerConnection.ISettings entirely, making the backend URL effectively immutable for the lifetime of the object, especially when memoizing the URL in a field.

Rule details

The rule reports every call expression of the form PageConfig.getBaseUrl(). The only legitimate call site is inside the ServerConnection.makeSettings() implementation itself, and in tests or examples.

Incorrect

// Stored on instance — URL can never change after construction
constructor(options: IOptions) {
  this._baseUrl = PageConfig.getBaseUrl();
}

// Captured in a closure at activation time
activate: (app: JupyterFrontEnd, paths: JupyterFrontEnd.IPaths) => {
  const url = URLExt.join(PageConfig.getBaseUrl(), paths.urls.themes);
  return new ThemeManager({ url });
};

Correct

// Access baseUrl from stored settings each time it is needed
private async _requestAPI<T>(): Promise<T> {
  const settings = this._serverSettings;
  const requestUrl = URLExt.join(settings.baseUrl, API_PATH);
  const response = await ServerConnection.makeRequest(requestUrl, {}, settings);
  ...
}

// Pass serverSettings through and read baseUrl when needed
activate: (app: JupyterFrontEnd) => {
  const serverSettings = app.serviceManager.serverSettings;
  return new MyManager({ serverSettings });
};

Options

This rule has no options.