Sub folders as modules needs "main" instead of "exports" in package.json

[kwasimensah]

Version

v18.9.1

Platform

Darwin 1.6.0 Darwin Kernel Version 21.6.0: Mon Aug 22 20:17:10 PDT 2022; root:xnu-8020.140.49~2/RELEASE_X86_64 x86_64

Subsystem

No response

What steps will reproduce the bug?

in https://github.com/kwasimensah/exports-not-loaded

1. run node test.js - fails with module not found error
2. Edit internal/foo/package.json to use "main" instead of "main_ignore"
3. node test.js now prints "Hello world"

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

Always

What is the expected behavior?

requiring internal/foo should work without specifying main in the package.json per the legacy banner at https://nodejs.org/docs/latest/api/modules.html#folders-as-modules

What do you see instead?

rror: Cannot find module 'internal/foo'
Require stack:
- /Users/kwasimensah/Documents/GitHub/exports-not-loaded/test.js
    at Module._resolveFilename (node:internal/modules/cjs/loader:955:15)
    at Module._load (node:internal/modules/cjs/loader:803:27)
    at Module.require (node:internal/modules/cjs/loader:1021:19)
    at require (node:internal/modules/cjs/helpers:103:18)
    at Object.<anonymous> (/Users/kwasimensah/Documents/GitHub/exports-not-loaded/test.js:1:13)
    at Module._compile (node:internal/modules/cjs/loader:1119:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1173:10)
    at Module.load (node:internal/modules/cjs/loader:997:32)
    at Module._load (node:internal/modules/cjs/loader:838:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12) {
  code: 'MODULE_NOT_FOUND',
  requireStack: [ '/Users/kwasimensah/Documents/GitHub/exports-not-loaded/test.js' ]
}

Additional information

The regex at

node/lib/internal/modules/cjs/loader.js

Line 538 in 73c0564

const EXPORTS_PATTERN = /^((?:@[^/\\%]+\/)?[^./\\%][^/\\%]*)(\/.*)?$/;

doesn't deal with subpaths. It's not directly clear why the request needs to be parsed and can't use use path.resolve/path.join

[Abhijrathod]

It seems that you are encountering an issue with the way Node.js is handling the "internal" modules when requiring a folder in your application. The error message "Cannot find module 'internal/foo'" indicates that Node.js is unable to locate the "internal/foo" folder when you try to require it in your test.js file.

It appears that the issue is related to the regular expression (EXPORTS_PATTERN) that is used to handle the "internal" modules in the Node.js CJS (CommonJS) loader. The regular expression is not able to handle subpaths, which is causing the issue.

It seems that you have found a workaround for this issue, which is to specify "main" in the package.json file of the "internal/foo" folder. This is allowing Node.js to locate the "internal/foo" folder and import it correctly.

However, as per the legacy banner at https://nodejs.org/docs/latest/api/modules.html#folders-as-modules, the requirement of specifying main in the package.json for internal modules is not expected.

It might be possible that this issue is fixed in a later version of Node.js. So, you can try updating your Node.js version and see if it resolves the issue. Additionally, you can try to file an issue on Node.js repository, so that the developers can investigate this issue.