module: fix ERR_INTERNAL_ASSERTION in CJS module loading

[vivek958]

Description

Fixes #60401

The loadCJSModule function in lib/internal/modules/esm/translators.js was not validating source content before passing it to the native compileFunctionForCJSLoader function. When source was null or undefined, this caused an internal assertion failure instead of throwing a meaningful error.

Changes

• Added source validation in loadCJSModule to check for null/undefined/empty source
• Throws ERR_INVALID_RETURN_PROPERTY_VALUE with descriptive message instead of internal assertion

Testing

The validation prevents the internal assertion that was occurring with custom loaders returning null source.

• Added test file: test/parallel/test-esm-loader-null-source.js
• Tests verify proper error handling for null/undefined/empty source
• Tests ensure ERR_INTERNAL_ASSERTION is not thrown

Checklist

• make -j4 test (UNIX) or vcbuild test (Windows) passes (will be verified by CI)
• commit message follows commit guidelines

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[aduh95]

The validation prevents the internal assertion that was occurring with custom loaders returning null source. Not yet tested due to my system limitations.

Could you add a test?

[vivek958]

Could you add a test?

done, added test case in second commit to verify the fix works correctly. The test covers null, undefined, and empty string source values to ensure ERR_INVALID_RETURN_PROPERTY_VALUE is thrown instead of ERR_INTERNAL_ASSERTION. @aduh95

[vivek958]

Friendly ping @nodejs/loaders - would appreciate any feedback when you have time!

[aduh95]

Suggested change

	try {
	await import('file:///test-null-source.js');
	console.log('ERROR: Should have thrown');
	process.exit(1);
	} catch (err) {
	// Should throw ERR_INVALID_RETURN_PROPERTY_VALUE, not ERR_INTERNAL_ASSERTION
	if (err.code === 'ERR_INTERNAL_ASSERTION') {
	console.log('FAIL: Got ERR_INTERNAL_ASSERTION');
	process.exit(1);
	}
	if (err.code === 'ERR_INVALID_RETURN_PROPERTY_VALUE') {
	console.log('PASS: Got expected error');
	process.exit(0);
	}
	console.log('ERROR: Got unexpected error:', err.code);
	process.exit(1);
	}
	await assert.rejects(import('file:///test-null-source.js'), { code: 'ERR_INVALID_RETURN_PROPERTY_VALUE' });

[aduh95]

Let's declare the function outside the string so it's easier to read and can be linted

Suggested change

	const result = spawnSync(
	process.execPath,
	[
	'--no-warnings',
	'--input-type=module',
	'--eval',
	`
	import { register } from 'node:module';
	// Register a custom loader that returns null source
	const code = 'export function load(url, context, next) {' +
	' if (url.includes("test-null-source")) {' +
	' return { format: "commonjs", source: null, shortCircuit: true };' +
	' }' +
	' return next(url);' +
	'}';
	register('data:text/javascript,' + encodeURIComponent(code));
	function load(url, context, next) {
	if (url.includes("test-null-source")) {
	return { format: "commonjs", source: null, shortCircuit: true };
	}
	return next(url);
	}
	const result = spawnSync(
	process.execPath,
	[
	'--no-warnings',
	'--input-type=module',
	'--eval',
	`
	import { register } from 'node:module';
	// Register a custom loader that returns null source
	register('data:text/javascript,export ' + encodeURIComponent(${load}));