esm: remove globalPreload hook (superseded by initialize)

PR-URL: nodejs#49144 Reviewed-By: Geoffrey Booth <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]>
alexfernandez · Nov 1, 2023 · 7d3c468 · 7d3c468
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diff --git a/doc/api/module.md b/doc/api/module.md
@@ -149,6 +149,9 @@ import('node:fs').then((esmFS) => {
 <!-- YAML
 added: v8.8.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/49144
+    description: Removed `globalPreload`.
   - version: v20.6.0
     pr-url: https://github.com/nodejs/node/pull/48842
     description: Added `initialize` hook to replace `globalPreload`.
@@ -674,79 +677,6 @@ export async function load(url, context, nextLoad) {
 In a more advanced scenario, this can also be used to transform an unsupported
 source to a supported one (see [Examples](#examples) below).
 
-#### `globalPreload()`
-
-<!-- YAML
-changes:
-  - version:
-    - v18.6.0
-    - v16.17.0
-    pr-url: https://github.com/nodejs/node/pull/42623
-    description: Add support for chaining globalPreload hooks.
--->
-
-> Stability: 1.0 - Early development
-
-> **Warning:** This hook will be removed in a future version. Use
-> [`initialize`][] instead. When a hooks module has an `initialize` export,
-> `globalPreload` will be ignored.
-
-* `context` {Object} Information to assist the preload code
-  * `port` {MessagePort}
-* Returns: {string} Code to run before application startup
-
-Sometimes it might be necessary to run some code inside of the same global
-scope that the application runs in. This hook allows the return of a string
-that is run as a sloppy-mode script on startup.
-
-Similar to how CommonJS wrappers work, the code runs in an implicit function
-scope. The only argument is a `require`-like function that can be used to load
-builtins like "fs": `getBuiltin(request: string)`.
-
-If the code needs more advanced `require` features, it has to construct
-its own `require` using  `module.createRequire()`.
-
-```mjs
-export function globalPreload(context) {
-  return `\
-globalThis.someInjectedProperty = 42;
-console.log('I just set some globals!');
-
-const { createRequire } = getBuiltin('module');
-const { cwd } = getBuiltin('process');
-
-const require = createRequire(cwd() + '/<preload>');
-// [...]
-`;
-}
-```
-
-Another argument is provided to the preload code: `port`. This is available as a
-parameter to the hook and inside of the source text returned by the hook. This
-functionality has been moved to the `initialize` hook.
-
-Care must be taken in order to properly call [`port.ref()`][] and
-[`port.unref()`][] to prevent a process from being in a state where it won't
-close normally.
-
-```mjs
-/**
- * This example has the application context send a message to the hook
- * and sends the message back to the application context
- */
-export function globalPreload({ port }) {
-  port.onmessage = (evt) => {
-    port.postMessage(evt.data);
-  };
-  return `\
-    port.postMessage('console.log("I went to the hook and back");');
-    port.onmessage = (evt) => {
-      eval(evt.data);
-    };
-  `;
-}
-```
-
 ### Examples
 
 The various module customization hooks can be used together to accomplish
@@ -1105,8 +1035,6 @@ returned object contains the following keys:
 [`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
 [`initialize`]: #initialize
 [`module`]: modules.md#the-module-object
-[`port.ref()`]: worker_threads.md#portref
-[`port.unref()`]: worker_threads.md#portunref
 [`register`]: #moduleregisterspecifier-parenturl-options
 [`string`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String
 [`util.TextDecoder`]: util.md#class-utiltextdecoder

diff --git a/lib/internal/modules/esm/hooks.js b/lib/internal/modules/esm/hooks.js
@@ -3,15 +3,13 @@
 const {
   ArrayPrototypePush,
   ArrayPrototypePushApply,
-  FunctionPrototypeCall,
   Int32Array,
   ObjectAssign,
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
   Promise,
   SafeSet,
   StringPrototypeSlice,
-  StringPrototypeStartsWith,
   StringPrototypeToUpperCase,
   globalThis,
 } = primordials;
@@ -33,7 +31,6 @@ const {
   ERR_INVALID_RETURN_VALUE,
   ERR_LOADER_CHAIN_INCOMPLETE,
   ERR_METHOD_NOT_IMPLEMENTED,
-  ERR_UNKNOWN_BUILTIN_MODULE,
   ERR_WORKER_UNSERIALIZABLE_ERROR,
 } = require('internal/errors').codes;
 const { exitCodes: { kUnfinishedTopLevelAwait } } = internalBinding('errors');
@@ -49,7 +46,6 @@ const {
   validateString,
 } = require('internal/validators');
 const {
-  emitExperimentalWarning,
   kEmptyObject,
 } = require('internal/util');
 
@@ -73,8 +69,6 @@ let importMetaInitializer;
 
 /**
  * @typedef {object} ExportedHooks
- * @property {Function} initialize Customizations setup hook.
- * @property {Function} globalPreload Global preload hook.
  * @property {Function} resolve Resolve hook.
  * @property {Function} load Load hook.
  */
@@ -89,13 +83,6 @@ let importMetaInitializer;
 
 class Hooks {
   #chains = {
-    /**
-     * Prior to ESM loading. These are called once before any modules are started.
-     * @private
-     * @property {KeyedHook[]} globalPreload Last-in-first-out list of preload hooks.
-     */
-    globalPreload: [],
-
     /**
      * Phase 1 of 2 in ESM loading.
      * The output of the `resolve` chain of hooks is passed into the `load` chain of hooks.
@@ -146,7 +133,6 @@ class Hooks {
 
   /**
    * Collect custom/user-defined module loader hook(s).
-   * After all hooks have been collected, the global preload hook(s) must be initialized.
    * @param {string} url Custom loader specifier
    * @param {Record<string, unknown>} exports
    * @param {any} [data] Arbitrary data to be passed from the custom loader (user-land)
@@ -155,18 +141,11 @@ class Hooks {
    */
   addCustomLoader(url, exports, data) {
     const {
-      globalPreload,
       initialize,
       resolve,
       load,
     } = pluckHooks(exports);
 
-    if (globalPreload && !initialize) {
-      emitExperimentalWarning(
-        '`globalPreload` is planned for removal in favor of `initialize`. `globalPreload`',
-      );
-      ArrayPrototypePush(this.#chains.globalPreload, { __proto__: null, fn: globalPreload, url });
-    }
     if (resolve) {
       const next = this.#chains.resolve[this.#chains.resolve.length - 1];
       ArrayPrototypePush(this.#chains.resolve, { __proto__: null, fn: resolve, url, next });
@@ -178,49 +157,6 @@ class Hooks {
     return initialize?.(data);
   }
 
-  /**
-   * Initialize `globalPreload` hooks.
-   */
-  initializeGlobalPreload() {
-    const preloadScripts = [];
-    for (let i = this.#chains.globalPreload.length - 1; i >= 0; i--) {
-      const { MessageChannel } = require('internal/worker/io');
-      const channel = new MessageChannel();
-      const {
-        port1: insidePreload,
-        port2: insideLoader,
-      } = channel;
-
-      insidePreload.unref();
-      insideLoader.unref();
-
-      const {
-        fn: preload,
-        url: specifier,
-      } = this.#chains.globalPreload[i];
-
-      const preloaded = preload({
-        port: insideLoader,
-      });
-
-      if (preloaded == null) { continue; }
-
-      if (typeof preloaded !== 'string') { // [2]
-        throw new ERR_INVALID_RETURN_VALUE(
-          'a string',
-          `${specifier} globalPreload`,
-          preload,
-        );
-      }
-
-      ArrayPrototypePush(preloadScripts, {
-        code: preloaded,
-        port: insidePreload,
-      });
-    }
-    return preloadScripts;
-  }
-
   /**
    * Resolve the location of the module.
    *
@@ -559,8 +495,9 @@ class HooksProxy {
         AtomicsWait(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 0);
         const response = this.#worker.receiveMessageSync();
         if (response == null || response.message.status === 'exit') { return; }
-        const { preloadScripts } = this.#unwrapMessage(response);
-        this.#executePreloadScripts(preloadScripts);
+
+        // ! This line catches initialization errors in the worker thread.
+        this.#unwrapMessage(response);
       }
 
       this.#isReady = true;
@@ -677,66 +614,12 @@ class HooksProxy {
   importMetaInitialize(meta, context, loader) {
     this.#importMetaInitializer(meta, context, loader);
   }
-
-  #executePreloadScripts(preloadScripts) {
-    for (let i = 0; i < preloadScripts.length; i++) {
-      const { code, port } = preloadScripts[i];
-      const { compileFunction } = require('vm');
-      const preloadInit = compileFunction(
-        code,
-        ['getBuiltin', 'port', 'setImportMetaCallback'],
-        {
-          filename: '<preload>',
-        },
-      );
-      let finished = false;
-      let replacedImportMetaInitializer = false;
-      let next = this.#importMetaInitializer;
-      const { BuiltinModule } = require('internal/bootstrap/realm');
-      // Calls the compiled preload source text gotten from the hook
-      // Since the parameters are named we use positional parameters
-      // see compileFunction above to cross reference the names
-      try {
-        FunctionPrototypeCall(
-          preloadInit,
-          globalThis,
-          // Param getBuiltin
-          (builtinName) => {
-            if (StringPrototypeStartsWith(builtinName, 'node:')) {
-              builtinName = StringPrototypeSlice(builtinName, 5);
-            } else if (!BuiltinModule.canBeRequiredWithoutScheme(builtinName)) {
-              throw new ERR_UNKNOWN_BUILTIN_MODULE(builtinName);
-            }
-            if (BuiltinModule.canBeRequiredByUsers(builtinName)) {
-              return require(builtinName);
-            }
-            throw new ERR_UNKNOWN_BUILTIN_MODULE(builtinName);
-          },
-          // Param port
-          port,
-          // setImportMetaCallback
-          (fn) => {
-            if (finished || typeof fn !== 'function') {
-              throw new ERR_INVALID_ARG_TYPE('fn', fn);
-            }
-            replacedImportMetaInitializer = true;
-            const parent = next;
-            next = (meta, context) => {
-              return fn(meta, context, parent);
-            };
-          },
-        );
-      } finally {
-        finished = true;
-        if (replacedImportMetaInitializer) {
-          this.#importMetaInitializer = next;
-        }
-      }
-    }
-  }
 }
 ObjectSetPrototypeOf(HooksProxy.prototype, null);
 
+// TODO(JakobJingleheimer): Remove this when loaders go "stable".
+let globalPreloadWarningWasEmitted = false;
+
 /**
  * A utility function to pluck the hooks from a user-defined loader.
  * @param {import('./loader.js).ModuleExports} exports
@@ -750,9 +633,6 @@ function pluckHooks({
 }) {
   const acceptedHooks = { __proto__: null };
 
-  if (globalPreload) {
-    acceptedHooks.globalPreload = globalPreload;
-  }
   if (resolve) {
     acceptedHooks.resolve = resolve;
   }
@@ -762,6 +642,12 @@ function pluckHooks({
 
   if (initialize) {
     acceptedHooks.initialize = initialize;
+  } else if (globalPreload && !globalPreloadWarningWasEmitted) {
+    process.emitWarning(
+      '`globalPreload` has been removed; use `initialize` instead.',
+      'UnsupportedWarning',
+    );
+    globalPreloadWarningWasEmitted = true;
   }
 
   return acceptedHooks;

diff --git a/lib/internal/modules/esm/utils.js b/lib/internal/modules/esm/utils.js
@@ -145,9 +145,7 @@ async function initializeHooks() {
     );
   }
 
-  const preloadScripts = hooks.initializeGlobalPreload();
-
-  return { __proto__: null, hooks, preloadScripts };
+  return hooks;
 }
 
 module.exports = {

diff --git a/lib/internal/modules/esm/worker.js b/lib/internal/modules/esm/worker.js
@@ -74,7 +74,8 @@ function wrapMessage(status, body) {
 }
 
 async function customizedModuleWorker(lock, syncCommPort, errorHandler) {
-  let hooks, preloadScripts, initializationError;
+  let hooks;
+  let initializationError;
   let hasInitializationError = false;
 
   {
@@ -91,9 +92,7 @@ async function customizedModuleWorker(lock, syncCommPort, errorHandler) {
 
 
   try {
-    const initResult = await initializeHooks();
-    hooks = initResult.hooks;
-    preloadScripts = initResult.preloadScripts;
+    hooks = await initializeHooks();
   } catch (exception) {
     // If there was an error while parsing and executing a user loader, for example if because a
     // loader contained a syntax error, then we need to send the error to the main thread so it can
@@ -107,7 +106,7 @@ async function customizedModuleWorker(lock, syncCommPort, errorHandler) {
   if (hasInitializationError) {
     syncCommPort.postMessage(wrapMessage('error', initializationError));
   } else {
-    syncCommPort.postMessage(wrapMessage('success', { preloadScripts }), preloadScripts.map(({ port }) => port));
+    syncCommPort.postMessage(wrapMessage('success'));
   }
 
   // We're ready, so unlock the main thread.