`--experimental-vm-modules` on Node 12 results in confusing dynamic callback error

[SimenB]

• Version: v12.16.3
• Platform: macOS
• Subsystem: ESM

What steps will reproduce the bug?

// file.js
import('fs')
  .then(() => {
    console.log('yay!');
  })
  .catch(error => {
    console.error('aww', error);
    process.exitCode = 1;
  });

Node 12 still has flagged ESM, so running this file results in the following:

$ node file.js
aww Error: Not supported
    at Object.<anonymous> (/Users/simen/oops/file.js:1:1)
    at Module._compile (internal/modules/cjs/loader.js:1133:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1153:10)
    at Module.load (internal/modules/cjs/loader.js:977:32)
    at Function.Module._load (internal/modules/cjs/loader.js:877:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)
    at internal/main/run_main_module.js:18:47

However, if you add --experimental-vm-modules, the error gets very confusing.

$ node --experimental-vm-modules file.js
aww TypeError [ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING]: A dynamic import callback was not specified.
    at exports.importModuleDynamicallyCallback (internal/process/esm_loader.js:35:9)
    at Object.<anonymous> (/Users/simen/oops/file.js:1:1)
    at Module._compile (internal/modules/cjs/loader.js:1133:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1153:10)
    at Module.load (internal/modules/cjs/loader.js:977:32)
    at Function.Module._load (internal/modules/cjs/loader.js:877:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)
    at internal/main/run_main_module.js:18:47 {
  code: 'ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING'
}

How often does it reproduce? Is there a required condition?

It always reproduces

What is the expected behavior?

Node should give the same warning as if the flag wasn't passed.

What do you see instead?

Node throws ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING instead.

Additional information

N/A

[himself65]

Related

node/lib/internal/bootstrap/pre_execution.js

Lines 407 to 429 in 90d35ad

	function initializeESMLoader() {
	// Create this WeakMap in js-land because V8 has no C++ API for WeakMap.
	internalBinding('module_wrap').callbackMap = new SafeWeakMap();
	const experimentalModules = getOptionValue('--experimental-modules');
	const experimentalVMModules = getOptionValue('--experimental-vm-modules');
	if (experimentalModules || experimentalVMModules) {
	if (experimentalModules) {
	process.emitWarning(
	'The ESM module loader is experimental.',
	'ExperimentalWarning', undefined);
	}
	const {
	setImportModuleDynamicallyCallback,
	setInitializeImportMetaObjectCallback
	} = internalBinding('module_wrap');
	const esm = require('internal/process/esm_loader');
	// Setup per-isolate callbacks that locate data or callbacks that we keep
	// track of for different ESM modules.
	setInitializeImportMetaObjectCallback(esm.initializeImportMetaObject);
	setImportModuleDynamicallyCallback(esm.importModuleDynamicallyCallback);
	}
	}

[targos]

Closed by #33055