module: refactor loader

PR-URL: #16874
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Bradley Farias <bradley.meck@gmail.com>

lib/internal/loader/ModuleWrap.js → lib/internal/loader/CreateDynamicModule.js

@@ -1,9 +1,6 @@
 'use strict';
 
-const {
-  ModuleWrap,
-  setImportModuleDynamicallyCallback
-} = internalBinding('module_wrap');
+const { ModuleWrap } = internalBinding('module_wrap');
 const debug = require('util').debuglog('esm');
 const ArrayJoin = Function.call.bind(Array.prototype.join);
 const ArrayMap = Function.call.bind(Array.prototype.map);
@@ -60,8 +57,4 @@ const createDynamicModule = (exports, url = '', evaluate) => {
   };
 };
 
-module.exports = {
-  createDynamicModule,
-  setImportModuleDynamicallyCallback,
-  ModuleWrap
-};
+module.exports = createDynamicModule;

lib/internal/loader/DefaultResolve.js

@@ -0,0 +1,84 @@
+'use strict';
+
+const { URL } = require('url');
+const CJSmodule = require('module');
+const internalURLModule = require('internal/url');
+const internalFS = require('internal/fs');
+const NativeModule = require('native_module');
+const { extname } = require('path');
+const { realpathSync } = require('fs');
+const preserveSymlinks = !!process.binding('config').preserveSymlinks;
+const errors = require('internal/errors');
+const { resolve: moduleWrapResolve } = internalBinding('module_wrap');
+const StringStartsWith = Function.call.bind(String.prototype.startsWith);
+
+const realpathCache = new Map();
+
+function search(target, base) {
+  if (base === undefined) {
+    // We cannot search without a base.
+    throw new errors.Error('ERR_MISSING_MODULE', target);
+  }
+  try {
+    return moduleWrapResolve(target, base);
+  } catch (e) {
+    e.stack; // cause V8 to generate stack before rethrow
+    let error = e;
+    try {
+      const questionedBase = new URL(base);
+      const tmpMod = new CJSmodule(questionedBase.pathname, null);
+      tmpMod.paths = CJSmodule._nodeModulePaths(
+        new URL('./', questionedBase).pathname);
+      const found = CJSmodule._resolveFilename(target, tmpMod);
+      error = new errors.Error('ERR_MODULE_RESOLUTION_LEGACY', target,
+                               base, found);
+    } catch (problemChecking) {
+      // ignore
+    }
+    throw error;
+  }
+}
+
+const extensionFormatMap = {
+  __proto__: null,
+  '.mjs': 'esm',
+  '.json': 'json',
+  '.node': 'addon',
+  '.js': 'commonjs'
+};
+
+function resolve(specifier, parentURL) {
+  if (NativeModule.nonInternalExists(specifier)) {
+    return {
+      url: specifier,
+      format: 'builtin'
+    };
+  }
+
+  let url;
+  try {
+    url = search(specifier, parentURL);
+  } catch (e) {
+    if (typeof e.message === 'string' &&
+        StringStartsWith(e.message, 'Cannot find module'))
+      e.code = 'MODULE_NOT_FOUND';
+    throw e;
+  }
+
+  if (!preserveSymlinks) {
+    const real = realpathSync(internalURLModule.getPathFromURL(url), {
+      [internalFS.realpathCacheKey]: realpathCache
+    });
+    const old = url;
+    url = internalURLModule.getURLFromFilePath(real);
+    url.search = old.search;
+    url.hash = old.hash;
+  }
+
+  const ext = extname(url.pathname);
+  return { url: `${url}`, format: extensionFormatMap[ext] || ext };
+}
+
+module.exports = resolve;
+// exported for tests
+module.exports.search = search;

lib/internal/loader/Loader.js

@@ -2,16 +2,16 @@
 
 const path = require('path');
 const { getURLFromFilePath, URL } = require('internal/url');
-
-const {
-  createDynamicModule,
-  setImportModuleDynamicallyCallback
-} = require('internal/loader/ModuleWrap');
+const errors = require('internal/errors');
 
 const ModuleMap = require('internal/loader/ModuleMap');
 const ModuleJob = require('internal/loader/ModuleJob');
-const ModuleRequest = require('internal/loader/ModuleRequest');
-const errors = require('internal/errors');
+const defaultResolve = require('internal/loader/DefaultResolve');
+const createDynamicModule = require('internal/loader/CreateDynamicModule');
+const translators = require('internal/loader/Translators');
+const { setImportModuleDynamicallyCallback } = internalBinding('module_wrap');
+const FunctionBind = Function.call.bind(Function.prototype.bind);
+
 const debug = require('util').debuglog('esm');
 
 // Returns a file URL for the current working directory.
@@ -40,105 +40,101 @@ function normalizeReferrerURL(referrer) {
  * the main module and everything in its dependency graph. */
 class Loader {
   constructor(base = getURLStringForCwd()) {
-    if (typeof base !== 'string') {
+    if (typeof base !== 'string')
       throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'base', 'string');
-    }
 
-    this.moduleMap = new ModuleMap();
     this.base = base;
+
+    // methods which translate input code or other information
+    // into es modules
+    this.translators = translators;
+
+    // registry of loaded modules, akin to `require.cache`
+    this.moduleMap = new ModuleMap();
+
     // The resolver has the signature
     //   (specifier : string, parentURL : string, defaultResolve)
-    //       -> Promise<{ url : string,
-    //                    format: anything in Loader.validFormats }>
+    //       -> Promise<{ url : string, format: string }>
     // where defaultResolve is ModuleRequest.resolve (having the same
     // signature itself).
     // If `.format` on the returned value is 'dynamic', .dynamicInstantiate
     // will be used as described below.
-    this.resolver = ModuleRequest.resolve;
-    // This hook is only called when resolve(...).format is 'dynamic' and has
-    // the signature
+    this._resolve = defaultResolve;
+    // This hook is only called when resolve(...).format is 'dynamic' and
+    // has the signature
     //   (url : string) -> Promise<{ exports: { ... }, execute: function }>
     // Where `exports` is an object whose property names define the exported
     // names of the generated module. `execute` is a function that receives
     // an object with the same keys as `exports`, whose values are get/set
     // functions for the actual exported values.
-    this.dynamicInstantiate = undefined;
-  }
-
-  hook({ resolve = ModuleRequest.resolve, dynamicInstantiate }) {
-    // Use .bind() to avoid giving access to the Loader instance when it is
-    // called as this.resolver(...);
-    this.resolver = resolve.bind(null);
-    this.dynamicInstantiate = dynamicInstantiate;
+    this._dynamicInstantiate = undefined;
   }
 
-  // Typechecking wrapper around .resolver().
   async resolve(specifier, parentURL = this.base) {
-    if (typeof parentURL !== 'string') {
-      throw new errors.TypeError('ERR_INVALID_ARG_TYPE',
-                                 'parentURL', 'string');
-    }
-
-    const { url, format } = await this.resolver(specifier, parentURL,
-                                                ModuleRequest.resolve);
+    if (typeof parentURL !== 'string')
+      throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'parentURL', 'string');
 
-    if (!Loader.validFormats.includes(format)) {
-      throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'format',
-                                 Loader.validFormats);
-    }
+    const { url, format } =
+      await this._resolve(specifier, parentURL, defaultResolve);
 
-    if (typeof url !== 'string') {
+    if (typeof url !== 'string')
       throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'url', 'string');
-    }
 
-    if (format === 'builtin') {
+    if (typeof format !== 'string')
+      throw new errors.TypeError('ERR_INVALID_ARG_TYPE', 'format', 'string');
+
+    if (format === 'builtin')
       return { url: `node:${url}`, format };
-    }
 
-    if (format !== 'dynamic') {
-      if (!ModuleRequest.loaders.has(format)) {
-        throw new errors.Error('ERR_UNKNOWN_MODULE_FORMAT', format);
-      }
-      if (!url.startsWith('file:')) {
-        throw new errors.Error('ERR_INVALID_PROTOCOL', url, 'file:');
-      }
-    }
+    if (format !== 'dynamic' && !url.startsWith('file:'))
+      throw new errors.Error('ERR_INVALID_PROTOCOL', url, 'file:');
 
     return { url, format };
   }
 
-  // May create a new ModuleJob instance if one did not already exist.
+  async import(specifier, parent = this.base) {
+    const job = await this.getModuleJob(specifier, parent);
+    const module = await job.run();
+    return module.namespace();
+  }
+
+  hook({ resolve, dynamicInstantiate }) {
+    // Use .bind() to avoid giving access to the Loader instance when called.
+    if (resolve !== undefined)
+      this._resolve = FunctionBind(resolve, null);
+    if (dynamicInstantiate !== undefined)
+      this._dynamicInstantiate = FunctionBind(dynamicInstantiate, null);
+  }
+
   async getModuleJob(specifier, parentURL = this.base) {
     const { url, format } = await this.resolve(specifier, parentURL);
     let job = this.moduleMap.get(url);
-    if (job === undefined) {
-      let loaderInstance;
-      if (format === 'dynamic') {
-        const { dynamicInstantiate } = this;
-        if (typeof dynamicInstantiate !== 'function') {
-          throw new errors.Error('ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK');
-        }
-
-        loaderInstance = async (url) => {
-          const { exports, execute } = await dynamicInstantiate(url);
-          return createDynamicModule(exports, url, (reflect) => {
-            debug(`Loading custom loader ${url}`);
-            execute(reflect.exports);
-          });
-        };
-      } else {
-        loaderInstance = ModuleRequest.loaders.get(format);
-      }
-      job = new ModuleJob(this, url, loaderInstance);
-      this.moduleMap.set(url, job);
+    if (job !== undefined)
+      return job;
+
+    let loaderInstance;
+    if (format === 'dynamic') {
+      if (typeof this._dynamicInstantiate !== 'function')
+        throw new errors.Error('ERR_MISSING_DYNAMIC_INTSTANTIATE_HOOK');
+
+      loaderInstance = async (url) => {
+        debug(`Translating dynamic ${url}`);
+        const { exports, execute } = await this._dynamicInstantiate(url);
+        return createDynamicModule(exports, url, (reflect) => {
+          debug(`Loading dynamic ${url}`);
+          execute(reflect.exports);
+        });
+      };
+    } else {
+      if (!translators.has(format))
+        throw new errors.RangeError('ERR_UNKNOWN_MODULE_FORMAT', format);
+
+      loaderInstance = translators.get(format);
     }
-    return job;
-  }
 
-  async import(specifier, parentURL = this.base) {
-    const job = await this.getModuleJob(specifier, parentURL);
-    const module = await job.run();
-    return module.namespace();
+    job = new ModuleJob(this, url, loaderInstance);
+    this.moduleMap.set(url, job);
+    return job;
   }
 
   static registerImportDynamicallyCallback(loader) {
@@ -147,6 +143,6 @@ class Loader {
     });
   }
 }
-Loader.validFormats = ['esm', 'cjs', 'builtin', 'addon', 'json', 'dynamic'];
+
 Object.setPrototypeOf(Loader.prototype, null);
 module.exports = Loader;