reject-import-system-module-from-non-system

Rejects static import declaration for system modules (.sys.mjs) from non-system modules.

Using static import for a system module into a non-system module would create a separate instance of the imported object(s) that is not shared with the other system modules and would break the per-process singleton expectation.

The reason for this is that inside system modules, a static import will load the module into the shared global. Inside non-system modules, the static import will load into a different global (e.g. window). This will cause the module to be loaded into different scopes, and hence create separate instances. The fix is to use ChromeUtils.importESModule which will import the object via the system module shared global scope.

Examples of incorrect code for this rule:

Inside a non-system module:

import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";

Examples of correct code for this rule:

Inside a non-system module:

const { AppConstants } = ChromeUtils.importESModule(
  "resource://gre/modules/AppConstants.sys.mjs"
);

Inside a system module:

import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";