module: ensure successful dynamic import returns the same result

Author: aduh95

lib/internal/modules/cjs/loader.js

@@ -1147,8 +1147,8 @@ function wrapSafe(filename, content, cjsModuleInstance) {
       lineOffset: 0,
       importModuleDynamically: async (specifier, _, importAssertions) => {
         const cascadedLoader = getCascadedLoader();
-        return cascadedLoader.import(specifier, normalizeReferrerURL(filename),
-                                     importAssertions);
+        return cascadedLoader.dynamicImport(specifier, normalizeReferrerURL(filename),
+                                            importAssertions);
       },
     });
 
@@ -1173,8 +1173,8 @@ function wrapSafe(filename, content, cjsModuleInstance) {
       filename,
       importModuleDynamically(specifier, _, importAssertions) {
         const cascadedLoader = getCascadedLoader();
-        return cascadedLoader.import(specifier, normalizeReferrerURL(filename),
-                                     importAssertions);
+        return cascadedLoader.dynamicImport(specifier, normalizeReferrerURL(filename),
+                                            importAssertions);
       },
     });
 

lib/internal/modules/esm/loader.js

@@ -7,7 +7,10 @@ const {
   Array,
   ArrayIsArray,
   FunctionPrototypeCall,
+  JSONStringify,
   ObjectSetPrototypeOf,
+  PromisePrototypeThen,
+  SafeMap,
   SafePromiseAllReturnArrayLike,
   SafeWeakMap,
 } = primordials;
@@ -71,6 +74,8 @@ class ESMLoader {
   #defaultLoad;
   #importMetaInitializer;
 
+  #dynamicImportCache = new SafeMap();
+
   /**
    * The conditions for resolving packages if `--conditions` is not used.
    */
@@ -124,7 +129,7 @@ class ESMLoader {
       const module = new ModuleWrap(url, undefined, source, 0, 0);
       setCallbackForWrap(module, {
         importModuleDynamically: (specifier, { url }, importAssertions) => {
-          return this.import(specifier, url, importAssertions);
+          return this.dynamicImport(specifier, url, importAssertions);
         }
       });
 
@@ -242,6 +247,41 @@ class ESMLoader {
     return job;
   }
 
+  async dynamicImport(specifier, parentURL, importAssertions) {
+    let cache = this.#dynamicImportCache.get(parentURL);
+    let specifierCache;
+    if (cache == null) {
+      this.#dynamicImportCache.set(parentURL, cache = new SafeMap());
+    } else {
+      specifierCache = cache.get(specifier);
+    }
+
+    if (specifierCache == null) {
+      cache.set(specifier, specifierCache = { __proto__: null });
+    }
+
+    const assertions = JSONStringify(importAssertions);
+    const removeCache = () => {
+      delete specifierCache[assertions];
+    };
+    if (specifierCache[assertions] != null) {
+      const fallback = () => {
+        if (specifierCache[assertions] != null) {
+          return PromisePrototypeThen(specifierCache[assertions], undefined, fallback);
+        }
+        const result = this.import(specifier, parentURL, importAssertions);
+        specifierCache[assertions] = result;
+        PromisePrototypeThen(result, undefined, removeCache);
+        return result;
+      };
+      return PromisePrototypeThen(specifierCache[assertions], undefined, fallback);
+    }
+    const result = this.import(specifier, parentURL, importAssertions);
+    specifierCache[assertions] = result;
+    PromisePrototypeThen(result, undefined, removeCache);
+    return result;
+  }
+
   /**
    * This method is usually called indirectly as part of the loading processes.
    * Internally, it is used directly to add loaders. Use directly with caution.
@@ -267,7 +307,9 @@ class ESMLoader {
     // create redundant work for the caller, so it is later popped off the
     // internal list.
     const wasArr = ArrayIsArray(specifiers);
-    if (!wasArr) { specifiers = [specifiers]; }
+    if (!wasArr) {
+      specifiers = [specifiers];
+    }
 
     const count = specifiers.length;
     const jobs = new Array(count);

lib/internal/modules/esm/translators.js

@@ -105,7 +105,7 @@ function errPath(url) {
 }
 
 async function importModuleDynamically(specifier, { url }, assertions) {
-  return asyncESM.esmLoader.import(specifier, url, assertions);
+  return asyncESM.esmLoader.dynamicImport(specifier, url, assertions);
 }
 
 // Strategy for loading a standard JavaScript module.

lib/internal/process/execution.js

@@ -86,7 +86,7 @@ function evalScript(name, body, breakFirstLine, print, shouldLoadESM = false) {
         [kVmBreakFirstLineSymbol]: !!breakFirstLine,
         importModuleDynamically(specifier, _, importAssertions) {
           const loader = asyncESM.esmLoader;
-          return loader.import(specifier, baseUrl, importAssertions);
+          return loader.dynamicImport(specifier, baseUrl, importAssertions);
         }
       }));
     if (print) {

lib/repl.js

@@ -73,9 +73,11 @@ const {
   ObjectKeys,
   ObjectSetPrototypeOf,
   Promise,
+  PromisePrototypeThen,
   ReflectApply,
   RegExp,
   RegExpPrototypeExec,
+  SafeMap,
   SafePromiseRace,
   SafeSet,
   SafeWeakSet,
@@ -455,12 +457,13 @@ function REPLServer(prompt,
           // Remove all "await"s and attempt running the script
           // in order to detect if error is truly non recoverable
           const fallbackCode = SideEffectFreeRegExpPrototypeSymbolReplace(/\bawait\b/g, code, '');
+          const dynamicImportCache = new SafeMap();
           try {
             vm.createScript(fallbackCode, {
               filename: file,
               displayErrors: true,
               importModuleDynamically: (specifier, _, importAssertions) => {
-                return asyncESM.esmLoader.import(specifier, parentURL,
+                return asyncESM.esmLoader.dynamicImport(specifier, parentURL,
                                                  importAssertions);
               }
             });
@@ -504,7 +507,7 @@ function REPLServer(prompt,
             filename: file,
             displayErrors: true,
             importModuleDynamically: (specifier, _, importAssertions) => {
-              return asyncESM.esmLoader.import(specifier, parentURL,
+              return asyncESM.esmLoader.dynamicImport(specifier, parentURL,
                                                importAssertions);
             }
           });

test/es-module/test-esm-dynamic-import-mutating-fs.js

@@ -0,0 +1,25 @@
+'use strict';
+const common = require('../common');
+const tmpdir = require('../common/tmpdir');
+
+const assert = require('node:assert');
+const fs = require('node:fs/promises');
+const { pathToFileURL } = require('node:url');
+
+tmpdir.refresh();
+const tmpDir = pathToFileURL(tmpdir.path);
+
+const target = new URL('./target.mjs', tmpDir);
+
+(async () => {
+
+  await assert.rejects(import(target), { code: 'ERR_MODULE_NOT_FOUND' });
+
+  await fs.writeFile(target, 'export default "actual target"\n');
+
+  const moduleRecord = await import(target);
+
+  await fs.rm(target);
+
+  assert.strictEqual(await import(target), moduleRecord);
+})().then(common.mustCall());

test/es-module/test-esm-dynamic-import-mutating-fs.mjs

@@ -0,0 +1,21 @@
+import '../common/index.mjs';
+import tmpdir from '../common/tmpdir.js';
+
+import assert from 'node:assert';
+import fs from 'node:fs/promises';
+import { pathToFileURL } from 'node:url';
+
+tmpdir.refresh();
+const tmpDir = pathToFileURL(tmpdir.path);
+
+const target = new URL('./target.mjs', tmpDir);
+
+await assert.rejects(import(target), { code: 'ERR_MODULE_NOT_FOUND' });
+
+await fs.writeFile(target, 'export default "actual target"\n');
+
+const moduleRecord = await import(target);
+
+await fs.rm(target);
+
+assert.strictEqual(await import(target), moduleRecord);