This PR fixes an issue where memfs throws ENOENT instead of the more semantically correct ENOTDIR when attempting to use a file as a directory on non-Windows platforms.

Problem

When trying to access a path that traverses through a file (e.g., /foo/bar where /foo is a file), memfs was throwing ENOENT: no such file or directory instead of ENOTDIR: not a directory. This behavior didn't match Node.js's platform-specific behavior:

// Before this fix
const { fs } = require('memfs');
fs.writeFileSync('/foo', 'hello');
fs.readFileSync('/foo/bar'); // throws ENOENT on all platforms

// Node.js behavior (what we should match)
const fs = require('node:fs');
fs.writeFileSync('/foo', 'hello');
fs.readFileSync('/foo/bar'); // throws ENOTDIR on Linux, ENOENT on Windows

Root Cause

The issue was in the walk method in src/core/Superblock.ts. When attempting to traverse through a non-directory, the error check was happening at the wrong time and wasn't accounting for symlink resolution.

Solution

1. Fixed the traversal logic: Added a check after symlink resolution to detect when attempting to traverse through a non-directory.

2. Added platform-specific behavior: Implemented platform-aware error codes to match Node.js behavior:

   • Non-Windows platforms: Throws ENOTDIR (more semantically correct)
   • Windows platform: Throws ENOENT (matches Node.js Windows behavior)

3. Preserved compatibility: The check only applies to filesystem operations (when checkExistence=true), ensuring internal APIs and symlink traversals continue to work correctly.

Changes

• src/core/Superblock.ts: Added platform-specific error handling after symlink resolution in the walk method
• src/node/__tests__/volume/readFileSync-enotdir.test.ts: Added comprehensive tests for both platform behaviors

The fix ensures that all file operations (readFileSync, writeFileSync, statSync, etc.) correctly handle file-as-directory scenarios while maintaining backward compatibility for valid operations and symlink traversals.

Fixes #1050.

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