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process: clarify the pre- and post-condition of esm setup
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This patch:

- Clarifies the dependency of the ESM loader initialization
  (`process.cwd()` and the value of `--loader`) in `node.js`.
- Moves the initialization of the per-isolate `importModuleDynamically`
  and `initializeImportMetaObject` callbacks into `node.js`
- Moves the initialization of the ESM loader into
  `prepareUserCodeExecution()` since it potentially involves
  execution of user code (similar to `--require` for CJS modules).

PR-URL: #25530
Reviewed-By: Gus Caplan <[email protected]>
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joyeecheung authored and addaleax committed Jan 23, 2019
1 parent ecd358b commit 647a37f
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Showing 2 changed files with 30 additions and 23 deletions.
35 changes: 24 additions & 11 deletions lib/internal/bootstrap/node.js
Original file line number Diff line number Diff line change
Expand Up @@ -210,17 +210,6 @@ function startup() {
'DeprecationWarning', 'DEP0062', startup, true);
}

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);
}
NativeModule.require('internal/process/esm_loader').setup();
}

const { deprecate } = NativeModule.require('internal/util');
{
// Install legacy getters on the `util` binding for typechecking.
Expand Down Expand Up @@ -451,6 +440,30 @@ function prepareUserCodeExecution() {
delete process.env.NODE_UNIQUE_ID;
}

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 = NativeModule.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);
const userLoader = getOptionValue('--loader');
// If --loader is specified, create a loader with user hooks. Otherwise
// create the default loader.
esm.initializeLoader(process.cwd(), userLoader);
}

// For user code, we preload modules if `-r` is passed
const preloadModules = getOptionValue('--require');
if (preloadModules) {
Expand Down
18 changes: 6 additions & 12 deletions lib/internal/process/esm_loader.js
Original file line number Diff line number Diff line change
@@ -1,8 +1,6 @@
'use strict';

const {
setImportModuleDynamicallyCallback,
setInitializeImportMetaObjectCallback,
callbackMap,
} = internalBinding('module_wrap');

Expand All @@ -15,16 +13,16 @@ const {
ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
} = require('internal/errors').codes;

function initializeImportMetaObject(wrap, meta) {
exports.initializeImportMetaObject = function(wrap, meta) {
if (callbackMap.has(wrap)) {
const { initializeImportMeta } = callbackMap.get(wrap);
if (initializeImportMeta !== undefined) {
initializeImportMeta(meta, wrapToModuleMap.get(wrap) || wrap);
}
}
}
};

async function importModuleDynamicallyCallback(wrap, specifier) {
exports.importModuleDynamicallyCallback = async function(wrap, specifier) {
if (callbackMap.has(wrap)) {
const { importModuleDynamically } = callbackMap.get(wrap);
if (importModuleDynamically !== undefined) {
Expand All @@ -33,10 +31,7 @@ async function importModuleDynamicallyCallback(wrap, specifier) {
}
}
throw new ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING();
}

setInitializeImportMetaObjectCallback(initializeImportMetaObject);
setImportModuleDynamicallyCallback(importModuleDynamicallyCallback);
};

let loaderResolve;
exports.loaderPromise = new Promise((resolve, reject) => {
Expand All @@ -45,13 +40,12 @@ exports.loaderPromise = new Promise((resolve, reject) => {

exports.ESMLoader = undefined;

exports.setup = function() {
exports.initializeLoader = function(cwd, userLoader) {
let ESMLoader = new Loader();
const loaderPromise = (async () => {
const userLoader = require('internal/options').getOptionValue('--loader');
if (userLoader) {
const hooks = await ESMLoader.import(
userLoader, pathToFileURL(`${process.cwd()}/`).href);
userLoader, pathToFileURL(`${cwd}/`).href);
ESMLoader = new Loader();
ESMLoader.hook(hooks);
exports.ESMLoader = ESMLoader;
Expand Down

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