vfs: address aduh95 code review comments

- Use kEmptyObject, optional chaining, primordials in memory.js
- Simplify openSync try/catch and readdir iteration
- Use parentPath instead of recomputing in ensureParent
- Explain readFileSync wrapper purpose in helpers.js
- Revert opts→options JSDoc rename in package_json_reader.js
- Restore internalFsBinding to module level in package_json_reader.js
- Add POSIX separator comment in embedding.js

Author: mcollina

lib/internal/main/embedding.js

@@ -93,6 +93,7 @@ function embedderRunCjs(content, filename) {
   // and use createRequire for a fully-featured require function.
   let requireFn;
   if (seaVfsActive && seaVfsMountPoint) {
+    // VFS paths always use POSIX separators regardless of platform.
     customModule.filename = seaVfsMountPoint + '/' + path.basename(filename);
     customModule.paths = Module._nodeModulePaths(
       path.dirname(customModule.filename));

lib/internal/modules/helpers.js

@@ -68,7 +68,8 @@ function toRealPath(requestPath) {
 }
 
 /**
- * Reads a file from disk.
+ * Reads a file from disk via the `fs` module reference, which may be
+ * monkey-patched by VFS to intercept reads for virtual paths.
  * @param {string} path The file path
  * @param {string|object} options Read options
  * @returns {string|Buffer}

lib/internal/modules/package_json_reader.js

@@ -25,6 +25,7 @@ const {
 } = require('internal/errors');
 const { kEmptyObject } = require('internal/util');
 const modulesBinding = internalBinding('modules');
+const internalFsBinding = internalBinding('fs');
 const path = require('path');
 const { validateString } = require('internal/validators');
 
@@ -115,7 +116,7 @@ const requiresJSONParse = (value) => (value !== undefined && (value[0] === '[' |
  *   base?: URL | string,
  *   specifier?: URL | string,
  *   isESM?: boolean,
- * }} opts
+ * }} options
  * @returns {PackageConfig}
  */
 function read(jsonPath, { base, specifier, isESM } = kEmptyObject) {
@@ -275,7 +276,6 @@ function getPackageJSONURL(specifier, base) {
     }
   }
 
-  const internalFsBinding = internalBinding('fs');
   let packageJSONUrl = new URL(`./node_modules/${packageName}/package.json`, base);
   let packageJSONPath = fileURLToPath(packageJSONUrl);
   let lastPath;

lib/internal/vfs/providers/memory.js

@@ -1,9 +1,11 @@
 'use strict';
 
 const {
+  ArrayFrom,
   ArrayPrototypePush,
   DateNow,
   SafeMap,
+  StringPrototypeReplaceAll,
   Symbol,
 } = primordials;
 
@@ -37,6 +39,7 @@ const {
   createSymlinkStats,
 } = require('internal/vfs/stats');
 const { Dirent } = require('internal/fs/utils');
+const { kEmptyObject } = require('internal/util');
 const {
   fs: {
     UV_DIRENT_FILE,
@@ -62,7 +65,7 @@ const kMaxSymlinkDepth = 40;
  * Internal entry representation for MemoryProvider.
  */
 class MemoryEntry {
-  constructor(type, options = {}) {
+  constructor(type, options = kEmptyObject) {
     this.type = type;
     this.mode = options.mode ?? (type === TYPE_DIR ? 0o755 : 0o644);
     this.content = null; // For files - static Buffer content
@@ -85,7 +88,7 @@ class MemoryEntry {
   getContentSync() {
     if (this.contentProvider !== null) {
       const result = this.contentProvider();
-      if (result && typeof result.then === 'function') {
+      if (typeof result?.then === 'function') {
         // It's a Promise - can't use sync API
         throw new ERR_INVALID_STATE('cannot use sync API with async content provider');
       }
@@ -171,9 +174,9 @@ class MemoryProvider extends VirtualProvider {
    */
   #normalizePath(path) {
     // Convert backslashes to forward slashes
-    let normalized = path.replace(/\\/g, '/');
+    let normalized = StringPrototypeReplaceAll(path, '\\', '/');
     // Ensure absolute path
-    if (!normalized.startsWith('/')) {
+    if (normalized[0] !== '/') {
       normalized = '/' + normalized;
     }
     // Use path.posix.normalize to resolve . and ..
@@ -368,8 +371,7 @@ class MemoryProvider extends VirtualProvider {
     }
 
     // Ensure final directory is populated
-    const finalPath = pathPosix.join('/', ...segments);
-    this.#ensurePopulated(current, finalPath);
+    this.#ensurePopulated(current, parentPath);
 
     return current;
   }
@@ -453,16 +455,13 @@ class MemoryProvider extends VirtualProvider {
     try {
       entry = this.#getEntry(normalized, 'open');
     } catch (err) {
-      if (err.code === 'ENOENT' && isCreate) {
-        // Create the file
-        const parent = this.#ensureParent(normalized, true, 'open');
-        const name = this.#getBaseName(normalized);
-        entry = new MemoryEntry(TYPE_FILE, { mode });
-        entry.content = Buffer.alloc(0);
-        parent.children.set(name, entry);
-      } else {
-        throw err;
-      }
+      if (err.code !== 'ENOENT' || !isCreate) throw err;
+      // Create the file
+      const parent = this.#ensureParent(normalized, true, 'open');
+      const name = this.#getBaseName(normalized);
+      entry = new MemoryEntry(TYPE_FILE, { mode });
+      entry.content = Buffer.alloc(0);
+      parent.children.set(name, entry);
     }
 
     if (entry.isDirectory()) {
@@ -509,13 +508,10 @@ class MemoryProvider extends VirtualProvider {
     // Ensure directory is populated (for lazy population)
     this.#ensurePopulated(entry, path);
 
-    const names = [...entry.children.keys()];
-
     if (options?.withFileTypes) {
       const normalized = this.#normalizePath(path);
       const dirents = [];
-      for (const name of names) {
-        const childEntry = entry.children.get(name);
+      for (const { 0: name, 1: childEntry } of entry.children) {
         let type;
         if (childEntry.isSymbolicLink()) {
           type = UV_DIRENT_LINK;
@@ -529,7 +525,7 @@ class MemoryProvider extends VirtualProvider {
       return dirents;
     }
 
-    return names;
+    return ArrayFrom(entry.children.keys());
   }
 
   async readdir(path, options) {