Post MVP: Specifying import policy for new contexts

[zenparsing]

Users should be able to specify an import policy for newly created contexts. By default, importing should not be allowed.

The previous implementation in vm.js allowed an importPolicy option to vm.createContext:

const ModuleLoader = require('internal/modules/esm/module_loader');
const { setModuleLoaderForContext } = internalBinding('module_wrap');

function validateImportPolicy(prop, propName) {
  if (prop === undefined)
    return;
  if (typeof prop.resolve !== 'function')
    throw new ERR_INVALID_ARG_TYPE(`${propName}.resolve`, 'Function', prop.resolve);
  if (typeof prop.load !== 'function')
    throw new ERR_INVALID_ARG_TYPE(`${propName}.resolve`, 'Function', prop.resolve);
}

function createContext(sandbox = {}, options = {}) {
  // ...

  validateImportPolicy(importPolicy, 'options.importPolicy');

  makeContext(sandbox, name, origin, strings, wasm);

  if (importPolicy) {
    setModuleLoaderForContext(sandbox, new ModuleLoader({
      context: sandbox,
      resolve: importPolicy.resolve,
      load: importPolicy.load
    }));
  }

  return sandbox;
}