module: add support for nodeEntryPointConfig.loaders in package.json

doc/api/packages.md

@@ -1315,10 +1315,36 @@ Package imports permit mapping to external packages.
 
 This field defines [subpath imports][] for the current package.
 
+### `nodeEntryPointConfig`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Object}
+
+Additional configuration on how to start the Node.js processes inside a package
+(does not apply if the entry point is using `.mjs` or `.cjs` file extension).
+
+#### `nodeEntryPointConfig.loaders`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {string\[]}
+
+Specify the `module` of a custom experimental [ECMAScript module loader][].
+`module` may be any string accepted as an [`import` specifier][] resolved
+relative to the `package.json` file.
+This field is ignored if the [`--experimental-loader`][] CLI flag is used.
+
+
 [Babel]: https://babeljs.io/
 [CommonJS]: modules.md
 [Conditional exports]: #conditional-exports
 [Corepack]: corepack.md
+[ECMAScript module loader]: esm.md#loaders
 [ES module]: esm.md
 [ES modules]: esm.md
 [Node.js documentation for this section]: https://github.com/nodejs/node/blob/HEAD/doc/api/packages.md#conditions-definitions
@@ -1329,9 +1355,11 @@ This field defines [subpath imports][] for the current package.
 [`"packageManager"`]: #packagemanager
 [`"type"`]: #type
 [`--conditions` / `-C` flag]: #resolving-user-conditions
+[`--experimental-loader`]: cli.md#--experimental-loadermodule
 [`--no-addons` flag]: cli.md#--no-addons
 [`ERR_PACKAGE_PATH_NOT_EXPORTED`]: errors.md#err_package_path_not_exported
 [`esm`]: https://github.com/standard-things/esm#readme
+[`import` specifier]: esm.md#import-specifiers
 [`package.json`]: #nodejs-packagejson-field-definitions
 [entry points]: #package-entry-points
 [folders as modules]: modules.md#folders-as-modules

lib/internal/modules/cjs/loader.js

@@ -314,10 +314,12 @@ function readPackage(requestPath) {
  try {
  const parsed = JSONParse(json);
  const filtered = {
+ __proto__: null,
  name: parsed.name,
  main: parsed.main,
  exports: parsed.exports,
  imports: parsed.imports,
+ nodeEntryPointConfig: parsed.nodeEntryPointConfig,
  type: parsed.type
  };
  packageJsonCache.set(jsonPath, filtered);

lib/internal/modules/esm/resolve.js

@@ -1080,7 +1080,7 @@ function throwIfUnsupportedURLScheme(parsed, experimentalNetworkImports) {
  }
 }
 
-async function defaultResolve(specifier, context = {}) {
+function defaultResolve(specifier, context = {}) {
  let { parentURL, conditions } = context;
  if (parentURL && policy?.manifest) {
  const redirects = policy.manifest.getDependencyMapper(parentURL);
@@ -1226,11 +1226,11 @@ const {
 
 if (policy) {
  const $defaultResolve = defaultResolve;
- module.exports.defaultResolve = async function defaultResolve(
+ module.exports.defaultResolve = function defaultResolve(
  specifier,
  context
  ) {
- const ret = await $defaultResolve(specifier, context);
+ const ret = $defaultResolve(specifier, context);
  // This is a preflight check to avoid data exfiltration by query params etc.
  policy.manifest.mightAllow(ret.url, () =>
  new ERR_MANIFEST_DEPENDENCY_MISSING(

lib/internal/modules/run_main.js

@@ -1,6 +1,8 @@
 'use strict';
 
 const {
+ ArrayPrototypeMap,
+ ArrayPrototypePushApply,
  ObjectCreate,
  StringPrototypeEndsWith,
 } = primordials;
@@ -11,6 +13,7 @@ const path = require('path');
 const {
  handleProcessExit,
 } = require('internal/modules/esm/handle_process_exit');
+const { validateArray } = require('internal/validators');
 
 function resolveMainPath(main) {
  // Note extension resolution for the main entry point can be deprecated in a
@@ -45,6 +48,22 @@ function shouldUseESMLoader(mainPath) {
  if (!mainPath || StringPrototypeEndsWith(mainPath, '.cjs'))
  return false;
  const pkg = readPackageScope(mainPath);
+ if (typeof pkg.data?.nodeEntryPointConfig === 'object') {
+ const { loaders } = pkg.data.nodeEntryPointConfig;
+ if (loaders != null) {
+ const { pathToFileURL } = require('internal/url');
+ const {
+ defaultResolve,
+ DEFAULT_CONDITIONS,
+ } = require('internal/modules/esm/resolve');
+ validateArray(loaders, 'nodeEntryPointConfig.loaders');
+ const context = { parentURL: pathToFileURL(pkg.path).href + '/', conditions: DEFAULT_CONDITIONS };
+ const resolvedLoaders =
+ ArrayPrototypeMap(loaders, (loaderSpecifier) => defaultResolve(loaderSpecifier, context).url);
+ ArrayPrototypePushApply(userLoaders, resolvedLoaders);
+ return true;
+ }
+ }
  return pkg && pkg.data.type === 'module';
 }
 

test/es-module/test-esm-loader-chaining.mjs

@@ -431,3 +431,27 @@ const commonArgs = [
  assert.match(stderr, /'load' hook's nextLoad\(\) context/);
  assert.strictEqual(status, 1);
 }
+
+{
+ const { status } = spawnSync(
+ process.execPath,
+ [
+ fixtures.path('es-module-loaders', 'package.json-loader-relative-url', 'entryPoint'),
+ ],
+ { encoding: 'utf8' },
+ );
+
+ assert.strictEqual(status, 0);
+}
+
+{
+ const { status } = spawnSync(
+ process.execPath,
+ [
+ fixtures.path('es-module-loaders', 'package.json-loader-package-name', 'entryPoint'),
+ ],
+ { encoding: 'utf8' },
+ );
+
+ assert.strictEqual(status, 0);
+}

test/es-module/test-esm-loader-search.js

@@ -10,8 +10,8 @@ const {
  defaultResolve: resolve
 } = require('internal/modules/esm/resolve');
 
-assert.rejects(
- resolve('target'),
+assert.throws(
+() => resolve('target'),
  {
  code: 'ERR_MODULE_NOT_FOUND',
  name: 'Error',

test/fixtures/es-module-loaders/package.json-loader-package-name/entryPoint

@@ -0,0 +1,3 @@
+#!/usr/bin/env node
+
+export {};

test/fixtures/es-module-loaders/package.json-loader-package-name/package.json

@@ -0,0 +1,6 @@
+{
+ "name": "somePackage",
+ "nodeEntryPointConfig": {
+ "loaders": ["extensionless-loader"]
+ }
+}

test/fixtures/es-module-loaders/package.json-loader-relative-url/entryPoint

@@ -0,0 +1,3 @@
+#!/usr/bin/env node
+
+export {};

test/fixtures/es-module-loaders/package.json-loader-relative-url/load-extensionless-as-esm.mjs

@@ -0,0 +1,9 @@
+const extensionlessPath = /\/[^.]+$/;
+
+export async function resolve(specifier, context, next) {
+ const n = await next(specifier.toString(), context);
+ if (n.format == null && extensionlessPath.test(n.url)) {
+ n.format = "module";
+ }
+ return n;
+}

test/fixtures/es-module-loaders/package.json-loader-relative-url/package.json

@@ -0,0 +1,6 @@
+{
+ "name": "package.json-loader-relative-url",
+ "nodeEntryPointConfig": {
+ "loaders": ["./load-extensionless-as-esm.mjs"]
+ }
+}