vfs: resolve inherited worker entry after --import

lib/internal/modules/run_main.js

@@ -171,9 +171,14 @@ function executeUserEntryPoint(main = process.argv[1]) {
     wrapModuleLoad(main, null, true);
   } else {
     const mainPath = resolvedMain || main;
-    const mainURL = getOptionValue('--entry-url') ? new URL(mainPath, getCWDURL()) : pathToFileURL(mainPath);
+    let mainURL = getOptionValue('--entry-url') ? new URL(mainPath, getCWDURL()) : pathToFileURL(mainPath);
 
     runEntryPointWithESMLoader((cascadedLoader) => {
+      // A worker's inherited --vfs-load source is only mounted once --import
+      // has run, so an entry point inside it can only be resolved now.
+      if (resolvedMain === undefined && getOptionValue('--vfs-load') !== '' && !getOptionValue('--entry-url')) {
+        mainURL = pathToFileURL(resolveMainPath(main) || main);
+      }
       // Note that if the graph contains unsettled TLA, this may never resolve
       // even after the event loop stops running.
       return cascadedLoader.import(mainURL, undefined, { __proto__: null }, undefined, true);

test/parallel/test-vfs-load.js

@@ -158,6 +158,31 @@ require('worker_threads').parentPort.postMessage('hello from worker in mount');
   assert.match(res.stdout, /hello from worker in mount/);
 }
 
+// The same with an --import preload, which defers the worker's mount until the
+// preload has run: its entry point is still resolved inside the mount, with the
+// extension search a file entry point gets.
+{
+  const dir = fixture('worker-import-app');
+  fs.mkdirSync(dir, { recursive: true });
+  fs.writeFileSync(path.join(dir, 'index.js'), `
+'use strict';
+const path = require('path');
+const { Worker } = require('worker_threads');
+const w = new Worker(path.join(__dirname, 'worker'));
+w.on('message', (m) => { console.log(m); process.exit(0); });
+w.on('error', (e) => { console.error(e); process.exit(1); });
+`);
+  fs.writeFileSync(path.join(dir, 'worker.js'), `
+'use strict';
+require('worker_threads').parentPort.postMessage('hello from worker in mount');
+`);
+  const preload = fixture('empty-preload.mjs');
+  fs.writeFileSync(preload, '');
+  const res = run(['--import', pathToFileURL(preload).href, `--vfs-load=${dir}`]);
+  assert.strictEqual(res.status, 0, res.stderr);
+  assert.match(res.stdout, /hello from worker in mount/);
+}
+
 // The same, for a worker whose nearest package.json inside the mount says
 // "module": the entry point's type is read from the mount rather than from
 // the real file system above the reserved mount point.