--preserve-symlinks-main doesn't work

[pauldraper]

Version

v17.0.1

Platform

Linux paul 5.4.0-90-generic #101-Ubuntu SMP Fri Oct 15 20:00:55 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

Create a package with a file and a symlink to a file in a different directory.

echo 'require("./lib.js")' > file.js
mkdir package
> package/lib.js
ln -rs file.js package/index.js

Run Node.js with the package as the entrypoint.

node --preserve-symlinks --preserve-symlinks-main ./package

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

The feature --preserve-symlinks-main works with some file structures and doesn't work with others (like the example). I haven't yet figured out the general rule.

What is the expected behavior?

Node.js runs without error.

Namely, the entry point /home/paul/example/package/index.js resolves ./lib.js to /home/paul/example/package/lib.js

What do you see instead?

Node.js errs:

node:internal/modules/cjs/loader:936
  throw err;
  ^

Error: Cannot find module './lib.js'
Require stack:
- /home/paul/example/file.js
    at Function.Module._resolveFilename (node:internal/modules/cjs/loader:933:15)
    at Function.Module._load (node:internal/modules/cjs/loader:778:27)
    at Module.require (node:internal/modules/cjs/loader:999:19)
    at require (node:internal/modules/cjs/helpers:102:18)
    at Object.<anonymous> (/home/paul/dev/example/file.js:1:1)
    at Module._compile (node:internal/modules/cjs/loader:1095:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1147:10)
    at Module.load (node:internal/modules/cjs/loader:975:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12) {
  code: 'MODULE_NOT_FOUND',
  requireStack: [ '/home/paul/example/file.js' ]
}

Notice that Node.js has resolved /home/paul/example/package/index.js to its realpath (/home/paul/example/file.js), causing module resolution to fail.

Additional information

The validity of the example can be confirmed by replacing the symlink with a hardlink (ln file.js package/index.js), after which module resolution works.

[dgoldstein0]

hm, the one thing that comes to mind is that I've only ever used --preserve-symlinks-main with full file paths. Does it repro with

node --preserve-symlinks --preserve-symlinks-main ./package/index.js

Also it was implemented before ESM was supported by default in node, so could be a commonjs vs ESM module loading issue.

[mrgrain]

I can easily reproduce this with npm:

$ node --preserve-symlinks --preserve-symlinks-main ./path/to/global/installs/node_modules/bin/npm --version

node:internal/modules/cjs/loader:1078
  throw err;
  ^

Error: Cannot find module '../lib/cli.js'

[dgoldstein0]

not sure I entirely understand your npm example but in general I would not expect --preserve-symlinks-main to be usable with a node_modules/.bin/thing main argument - thing there would be a symlink into an entirely different folder, probably node_modules/thing/cli.js or similar, and then require()s or imports in cli.js should be resolved relative to node_modules/thing/cli.js, not the node_modules/.bin/thing. So I don't think your npm example is a valid reproduction.