WIP Make CJS suggestions when file ext is not provided

lib/internal/modules/cjs/loader.js

@@ -879,7 +879,7 @@ function getExportsForCircularRequire(module) {
 // 2. If the module is native: call
 //    `NativeModule.prototype.compileForPublicLoader()` and return the exports.
 // 3. Otherwise, create a new module for the file and save it to the cache.
-//    Then have it load  the file contents before returning its exports
+//    Then have it load the file contents before returning its exports
 //    object.
 Module._load = function(request, parent, isMain) {
   let relResolveCacheIdentifier;

lib/internal/modules/esm/default_resolve.js

@@ -9,6 +9,10 @@ const { NativeModule } = require('internal/bootstrap/loaders');
 const { extname } = require('path');
 const { realpathSync } = require('fs');
 const { getOptionValue } = require('internal/options');
+const {
+  Module: CJSModule
+} = require('internal/modules/cjs/loader');
+
 
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
@@ -93,7 +97,32 @@ function resolve(specifier, parentURL) {
       throw new ERR_INPUT_TYPE_NOT_ALLOWED();
   }
 
-  let url = moduleWrapResolve(specifier, parentURL);
+  let url;
+  try {
+    url = moduleWrapResolve(specifier, parentURL);
+  } catch (error) {
+    try {
+      // By default ES Modules does not support extensionless files.
+      // The idea is make suggestions when file ext is not provided
+      // Example: import pkg from './meow'
+      // Ref: https://github.com/nodejs/node/issues/30603
+
+      // Create a fake CJS Module using parentURL.
+      const currentModule = new CJSModule(parentURL);
+      // Resolve our especifier e.g: 'file'
+      // using as module parent our current module.
+      // So with our fake parent, paths to search in CJS will be provided.
+      const cjsResolved = CJSModule._resolveFilename(specifier,
+                                                     currentModule,
+                                                     false);
+      if (cjsResolved) {
+        error.message += '\nCJS would resolved: ' + cjsResolved;
+      }
+    } catch (cjsError) { // eslint-disable-line no-unused-vars
+      // ignore
+    }
+    throw error;
+  }
 
   if (isMain ? !preserveSymlinksMain : !preserveSymlinks) {
     const real = realpathSync(fileURLToPath(url), {

test/es-module/test-esm-cjs-loader-suggestions.mjs

@@ -0,0 +1,4 @@
+import '../common/index.mjs';
+
+import('../fixtures/es-modules/cjs')
+  .catch(err => console.error(err))

test/message/esm_loader_not_found.out

@@ -1,8 +1,8 @@
 (node:*) ExperimentalWarning: The ESM module loader is experimental.
 (node:*) ExperimentalWarning: --experimental-loader is an experimental feature. This feature could change at any time
 internal/modules/esm/default_resolve.js:*
-  let url = moduleWrapResolve(specifier, parentURL);
-            ^
+    url = moduleWrapResolve(specifier, parentURL);
+          ^
 
 Error: Cannot find package 'i-dont-exist' imported from *
     at Loader.resolve [as _resolve] (internal/modules/esm/default_resolve.js:*:*)