node:fs: recursive readdir names each entry by its full path with the leading slash dropped #7678

readdirSync(dir, { recursive: true }) returns each entry as its full path minus the leading slash. Node.js returns it relative to dir. With withFileTypes: true, Dirent.name carries the same full path, where Node.js gives the entry's own name; parentPath is already right.

Reproduced on workerd 1.20261009.1 from npm, and the source it comes from is unchanged on main at e3449da.

Repro

repro.wd-test:

using Workerd = import "/workerd/workerd.capnp";

const unitTests :Workerd.Config = (
  services = [
    ( name = "repro",
      worker = (
        modules = [ (name = "worker", esModule = embed "repro.js") ],
        compatibilityDate = "2026-10-01",
      )
    ),
  ],
);

repro.js:

import { mkdirSync, writeFileSync, readdirSync } from 'node:fs';
import { deepStrictEqual } from 'node:assert';

export const recursiveReaddirNamesAreRelativeToTheDirectory = {
  test() {
    mkdirSync('/tmp/d/sub', { recursive: true });
    writeFileSync('/tmp/d/a.txt', 'a');
    writeFileSync('/tmp/d/sub/b.txt', 'b');

    // Node.js: ['a.txt', 'sub', 'sub/b.txt']
    deepStrictEqual(readdirSync('/tmp/d', { recursive: true }).sort(), ['a.txt', 'sub', 'sub/b.txt']);

    // Node.js: name is the entry's own name; parentPath is the directory holding it
    const ents = readdirSync('/tmp/d', { recursive: true, withFileTypes: true })
      .map((e) => [e.name, e.parentPath])
      .sort();
    deepStrictEqual(ents, [['a.txt', '/tmp/d'], ['b.txt', '/tmp/d/sub'], ['sub', '/tmp/d']]);
  },
};

workerd test repro.wd-test fails on the first assertion:

+ actual - expected
+ [ 'tmp/d/a.txt', 'tmp/d/sub', 'tmp/d/sub/b.txt' ]
- [ 'a.txt', 'sub', 'sub/b.txt' ]

The same repro.js passes under Node.js v26.11.0, with each test() called directly against the real /tmp.

Where it comes from

FileSystemModule::readdir starts readdirImpl from the absolute normalizedPath (filesystem.c++#L1279). In recursive mode, readdirImpl then names every entry path.append(entry.key).toString(false) (#L1217), which is that absolute path without its leading slash. A non-recursive read uses entry.key and matches Node.js.

Node.js names a string result by its path relative to the directory passed in, and a Dirent by its own name, with the directory in parentPath. readdirSync builds both from the same handle.name (internal_fs_sync.ts#L550-L573). So the handle would need to carry both the relative path and the bare name, or readdirImpl would need to know which one the caller wants. readdir and fs/promises both go through readdirSync, so they share the bug and the fix.

Why the existing tests pass

fs-dir-test.js only reads recursively from /. From the root, "relative to the directory" and "absolute minus the leading slash" are the same strings, so string results look right. For Dirents, the test asserts today's output: strictEqual(ents[1].name, 'bundle/worker') with parentPath /bundle (#L645, and again at L743 and L820). Node.js gives worker there, so a fix changes those three assertions. I'm not sure whether that needs a compat flag; that's your call.

Impact

Node.js code that walks a tree with readdirSync(dir, { recursive: true }) and joins each entry onto dir builds /tmp/d/tmp/d/a.txt and gets ENOENT. I hit it running a Node.js test suite inside workerd: a test that lists src/pages recursively went looking for /bundle/src/pages/bundle/src/pages/access/index.html.