vfs: add Symbol.dispose support for automatic unmount

VirtualFileSystem now supports the Explicit Resource Management proposal.
The mount() method returns the VFS instance, allowing use with the
'using' declaration for automatic cleanup when leaving scope.

Author: mcollina

doc/api/vfs.md

@@ -241,6 +241,7 @@ added: REPLACEME
 -->
 
 * `prefix` {string} The path prefix where the VFS will be mounted.
+* Returns: {VirtualFileSystem} The VFS instance (for chaining or `using`).
 
 Mounts the virtual file system at the specified path prefix. After mounting,
 files in the VFS can be accessed via the `fs` module using paths that start
@@ -263,6 +264,24 @@ myVfs.mount('/virtual');
 require('node:fs').readFileSync('/virtual/data.txt', 'utf8'); // 'Hello'
 ```
 
+The VFS supports the [Explicit Resource Management][] proposal. Use the `using`
+declaration to automatically unmount when leaving scope:
+
+```cjs
+const vfs = require('node:vfs');
+const fs = require('node:fs');
+
+{
+  using myVfs = vfs.create();
+  myVfs.writeFileSync('/data.txt', 'Hello');
+  myVfs.mount('/virtual');
+
+  fs.readFileSync('/virtual/data.txt', 'utf8'); // 'Hello'
+} // VFS is automatically unmounted here
+
+fs.existsSync('/virtual/data.txt'); // false - VFS is unmounted
+```
+
 ### `vfs.mounted`
 
 <!-- YAML
@@ -874,5 +893,6 @@ This is particularly dangerous because:
 * **Limit VFS usage**: Only use VFS in controlled environments where you trust
   all loaded modules.
 
+[Explicit Resource Management]: https://github.com/tc39/proposal-explicit-resource-management
 [Security considerations]: #security-considerations
 [Single Executable Applications]: single-executable-applications.md

lib/internal/vfs/file_system.js

@@ -3,6 +3,7 @@
 const {
   ObjectFreeze,
   Symbol,
+  SymbolDispose,
 } = primordials;
 
 const {
@@ -233,6 +234,7 @@ class VirtualFileSystem {
     if (this[kVirtualCwdEnabled]) {
       this._hookProcessCwd();
     }
+    return this;
   }
 
   /**
@@ -249,6 +251,16 @@ class VirtualFileSystem {
     this[kVirtualCwd] = null; // Reset virtual cwd on unmount
   }
 
+  /**
+   * Disposes of the VFS by unmounting it.
+   * Supports the Explicit Resource Management proposal (using declaration).
+   */
+  [SymbolDispose]() {
+    if (this[kMounted]) {
+      this.unmount();
+    }
+  }
+
   /**
    * Hooks process.chdir and process.cwd to support virtual cwd.
    * @private

test/parallel/test-vfs-basic.js

@@ -297,3 +297,55 @@ const vfs = require('node:vfs');
   assert.strictEqual(myVfs.existsSync('/dest.txt'), true);
   assert.strictEqual(myVfs.readFileSync('/dest.txt', 'utf8'), 'copy me');
 }
+
+// Test Symbol.dispose unmounts the VFS
+{
+  const myVfs = vfs.create();
+  myVfs.writeFileSync('/file.txt', 'content');
+  myVfs.mount('/virtual');
+
+  assert.strictEqual(myVfs.mounted, true);
+
+  // Call Symbol.dispose directly
+  myVfs[Symbol.dispose]();
+
+  assert.strictEqual(myVfs.mounted, false);
+}
+
+// Test Symbol.dispose is safe to call when not mounted
+{
+  const myVfs = vfs.create();
+  myVfs.writeFileSync('/file.txt', 'content');
+
+  assert.strictEqual(myVfs.mounted, false);
+
+  // Should not throw
+  myVfs[Symbol.dispose]();
+
+  assert.strictEqual(myVfs.mounted, false);
+}
+
+// Test Symbol.dispose is safe to call multiple times
+{
+  const myVfs = vfs.create();
+  myVfs.writeFileSync('/file.txt', 'content');
+  myVfs.mount('/virtual');
+
+  myVfs[Symbol.dispose]();
+  assert.strictEqual(myVfs.mounted, false);
+
+  // Should not throw when called again
+  myVfs[Symbol.dispose]();
+  assert.strictEqual(myVfs.mounted, false);
+}
+
+// Test mount() returns the VFS instance for chaining
+{
+  const myVfs = vfs.create();
+  myVfs.writeFileSync('/file.txt', 'content');
+
+  const result = myVfs.mount('/virtual');
+  assert.strictEqual(result, myVfs);
+
+  myVfs.unmount();
+}