vfs: fix package lookup on Windows

Author: mcollina

lib/internal/modules/helpers.js

@@ -12,6 +12,7 @@ const {
   ReflectApply,
   SafeMap,
   SafeSet,
+  Symbol,
   StringPrototypeCharCodeAt,
   StringPrototypeIncludes,
   StringPrototypeSlice,
@@ -93,6 +94,10 @@ const nativeLoaderMethods = {
   getResolutionRoot: () => undefined,
 };
 const loaderMethodKeys = ObjectKeys(nativeLoaderMethods);
+// Overrides use this sentinel when they handled a request but their method's
+// meaningful result is `undefined`. A plain `undefined` means fall through to
+// the native implementation.
+const kLoaderOverrideNoResult = Symbol('kLoaderOverrideNoResult');
 const loaderOverrides = new SafeMap();
 let hasLoaderOverrides = false;
 
@@ -109,6 +114,7 @@ function wrapLoaderMethod(key, originalFn) {
       const override = MapPrototypeGet(loaderOverrides, key);
       if (override !== undefined) {
         const result = ReflectApply(override, undefined, args);
+        if (result === kLoaderOverrideNoResult) return undefined;
         if (result !== undefined) { return result; }
       }
     }
@@ -688,6 +694,7 @@ module.exports = {
   initializeCjsConditions,
   legacyMainResolveExtensions,
   legacyMainResolveExtensionsIndexes,
+  kLoaderOverrideNoResult,
   loaderMethods,
   loadBuiltinModuleForEmbedder,
   loadBuiltinModule,

lib/internal/vfs/setup.js

@@ -784,6 +784,7 @@ function installModuleLoaderOverrides() {
   const {
     legacyMainResolveExtensions,
     legacyMainResolveExtensionsIndexes,
+    kLoaderOverrideNoResult,
     setLoaderOverrides,
   } = require('internal/modules/helpers');
   const { kResolvedByMainIndexNode } = legacyMainResolveExtensionsIndexes;
@@ -854,12 +855,12 @@ function installModuleLoaderOverrides() {
       const r = findVFS(jsonPath);
       if (r === null) return undefined;
       const { vfs } = r;
-      if (vfsStat(vfs, jsonPath) !== 0) return undefined;
+      if (vfsStat(vfs, jsonPath) !== 0) return kLoaderOverrideNoResult;
       let content;
       try {
         content = vfs.readFileSync(jsonPath);
       } catch {
-        return undefined;
+        return kLoaderOverrideNoResult;
       }
       // Both CJS and ESM raise ERR_INVALID_PACKAGE_CONFIG since
       // nodejs/node#48606.
@@ -870,7 +871,7 @@ function installModuleLoaderOverrides() {
       const r = findVFS(checkPath);
       if (r === null) return undefined;
       const found = findVFSPackageJSON(r.vfs, checkPath, r.normalized);
-      return found.tuple;
+      return found.tuple ?? kLoaderOverrideNoResult;
     },
     getPackageScopeConfig(resolved) {
       let filePath;
@@ -908,7 +909,7 @@ function installModuleLoaderOverrides() {
         const type = found.tuple[2];
         if (type === 'module' || type === 'commonjs') return type;
       }
-      return undefined;
+      return kLoaderOverrideNoResult;
     },
   });
 }

test/parallel/test-vfs-invalid-package-json.js

@@ -65,10 +65,12 @@ const vfs = require('node:vfs');
   myVfs.mkdirSync('/outer2/inner', { recursive: true });
   myVfs.writeFileSync('/outer2/package.json', '{ bad }');
   myVfs.writeFileSync('/outer2/inner/mod.js', 'export const x = 1;');
-  const mountPoint = myVfs.mount();
+  myVfs.mount();
 
-  await assert.rejects(() => import(`${mountPoint}/outer2/inner/mod.js`),
-                       { code: 'ERR_INVALID_PACKAGE_CONFIG' });
+  await assert.rejects(
+    () => import(`${myVfs.mountPointURL}/outer2/inner/mod.js`),
+    { code: 'ERR_INVALID_PACKAGE_CONFIG' },
+  );
 
   myVfs.unmount();
 })().then(common.mustCall());