`require('#x')` subpath imports fail with MODULE_NOT_FOUND under `--experimental-package-map`

[christopher-buss]

Version

v26.10.0 (also v26.8.1)

Platform

Microsoft Windows NT 10.0.26100.0 x64
, package maps

Subsystem

module, package maps

What steps will reproduce the bug?

A CommonJS module cannot require() one of its own package's "imports" entries when a package map is active. ESM import of the same specifier works.

pkg/package.json   {"name":"pkg","version":"1.0.0","imports":{"#*":"./src/*"},"main":"./index.cjs"}
pkg/index.cjs      module.exports = require('#util.cjs');
pkg/src/util.cjs   module.exports = 'ok';
app/package.json   {"type":"module"}
app/a.cjs          console.log(require('pkg'));
map.json           {"packages":{"app":{"url":"./app","dependencies":{"pkg":"pkg"}},"pkg":{"url":"./pkg","dependencies":{}}}}

$ node --experimental-package-map=map.json app/a.cjs
Error: Cannot find module '#util.cjs'

How often does it reproduce? Is there a required condition?

Always, when --experimental-package-map is set and a CommonJS module requires a # specifier.

What is the expected behavior? Why is that the expected behavior?

ok is printed, as it is without the flag.

The require() algorithm in modules.md runs LOAD_PACKAGE_IMPORTS (step 4) and LOAD_PACKAGE_SELF (step 5) before LOAD_PACKAGE_MAP (step 6). The ESM resolver also sends # specifiers to packageImportsResolve and asks the map only in packageResolve.

What do you see instead?

Error: Cannot find module '#util.cjs'
  code: 'MODULE_NOT_FOUND'

Additional information

Cause, in lib/internal/modules/cjs/loader.js (main at c89ec29):

• Module._resolveFilename calls tryPackageMapResolveCJS for every request that is not relative and not absolute. # requests are included.
• tryPackageMapResolveCJS throws MODULE_NOT_FOUND when the map has no entry for the request.
• The # imports block is never reached.

Suggested fix: do the map lookup after the # imports step (and after trySelf), as the documented algorithm does, or skip the lookup for requests that start with #.

Published packages that use "imports" from CommonJS fail to load under a package map. For example, dependency-cruiser 18.2.0 has require("#utl/try-require.cjs") in src/extract/transpile/vue-template-wrap.cjs. I found it through pnpm's nodeExperimentalPackageMap setting.

This was triaged using Opus 5.5 but verified by me to the best of my ability and filed by myself.