loader: fix esm resolve for symlink file

Fix: nodejs#42195

PR-URL: nodejs#42197
Fixes: nodejs#42195
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>

lib/internal/modules/esm/resolve.js

@@ -374,18 +374,24 @@ function finalizeResolution(resolved, base, preserveSymlinks) {
       resolved.pathname, 'must not include encoded "/" or "\\" characters',
       fileURLToPath(base));
 
-  const path = fileURLToPath(resolved);
+  let path = fileURLToPath(resolved);
   if (getOptionValue('--experimental-specifier-resolution') === 'node') {
     let file = resolveExtensionsWithTryExactName(resolved);
-    if (file !== undefined) return file;
-    if (!StringPrototypeEndsWith(path, '/')) {
-      file = resolveDirectoryEntry(new URL(`${resolved}/`));
-      if (file !== undefined) return file;
-    } else {
-      return resolveDirectoryEntry(resolved) || resolved;
+
+    // Directory
+    if (file === undefined) {
+      file = StringPrototypeEndsWith(path, '/') ?
+        (resolveDirectoryEntry(resolved) || resolved) : resolveDirectoryEntry(new URL(`${resolved}/`));
+
+      if (file === resolved) return file;
+
+      if (file === undefined) {
+        throw new ERR_MODULE_NOT_FOUND(
+          resolved.pathname, fileURLToPath(base), 'module');
+      }
     }
-    throw new ERR_MODULE_NOT_FOUND(
-      resolved.pathname, fileURLToPath(base), 'module');
+
+    path = file;
   }
 
   const stats = tryStatSync(StringPrototypeEndsWith(path, '/') ?

test/es-module/test-esm-specifiers-symlink.mjs

@@ -0,0 +1,40 @@
+import * as common from '../common/index.mjs';
+import path from 'path';
+import fs from 'fs/promises';
+import tmpdir from '../common/tmpdir.js';
+import { spawn } from 'child_process';
+import assert from 'assert';
+
+tmpdir.refresh();
+const tmpDir = tmpdir.path;
+
+// Create the following file structure:
+// ├── index.mjs
+// ├── subfolder
+// │   ├── index.mjs
+// │   └── node_modules
+// │       └── package-a
+// │           └── index.mjs
+// └── symlink.mjs -> ./subfolder/index.mjs
+const entry = path.join(tmpDir, 'index.mjs');
+const symlink = path.join(tmpDir, 'symlink.mjs');
+const real = path.join(tmpDir, 'subfolder', 'index.mjs');
+const packageDir = path.join(tmpDir, 'subfolder', 'node_modules', 'package-a');
+const packageEntry = path.join(packageDir, 'index.mjs');
+try {
+  await fs.symlink(real, symlink);
+} catch (err) {
+  if (err.code !== 'EPERM') throw err;
+  common.skip('insufficient privileges for symlinks');
+}
+await fs.mkdir(packageDir, { recursive: true });
+await Promise.all([
+  fs.writeFile(entry, 'import "./symlink.mjs";'),
+  fs.writeFile(real, 'export { a } from "package-a/index.mjs"'),
+  fs.writeFile(packageEntry, 'export const a = 1;'),
+]);
+
+spawn(process.execPath, ['--experimental-specifier-resolution=node', entry],
+      { stdio: 'inherit' }).on('exit', common.mustCall((code) => {
+  assert.strictEqual(code, 0);
+}));