Running any script with pnp on node 13.0.1: "TypeError: paths is not iterable"

[sverweij]

Do you want to request a feature or report a bug?
A bug (or I'm doing something stupid...)

What is the current behavior?

• On node 13 running a lifecycle script with yarn (with pnp enabled) errors with TypeError: paths is not iterable (see below).
• With the same files, on node 12 the script runs ok.

/home/runner/work/yarn-on-node-13/yarn-on-node-13/.pnp.js:747
    for (const path of paths) {
                       ^

TypeError: paths is not iterable
    at Function.Module._findPath (/home/runner/work/yarn-on-node-13/yarn-on-node-13/.pnp.js:747:24)
    at resolveMainPath (internal/bootstrap/pre_execution.js:447:28)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1046:24)
    at internal/main/run_main_module.js:16:11

If the current behavior is a bug, please provide the steps to reproduce.

On node 13, with yarn plug'n play enabled, run any javascript through yarn.

I've created a minimum reproduction repo on sverweij/yarn-on-node-13
In there: run yarn cache clean && yarn && yarn test
(You can see what happens in the GitHub actions tab of the repo...

• ...here for yarn 1.19.1 and
• ... here for yarn 2.0.0-rc.6)

What is the expected behavior?

The lifecycle script runs without errors (just like on node 12).

Please mention your node.js, yarn and operating system version.

node.js: 13.0.1
yarn: 1.19.1 (and 2.0.0-rc.6)
OS: macOS 10.14.6

[arcanis]

Can you check whether the same is true for Yarn v2?

[sverweij]

it is - check out this run with the same repo using yarn 2.0.0-rc.6: https://github.com/sverweij/yarn-on-node-13/runs/272305615

[sverweij]

Some research:

• on node 12 (and below) with the MRS above the Module._findPath as patched in .pnp.js is never called
• on node 13 it is, and it gets these arguments passed:

{
  '0': '/Users/sander/path/to/index.js',
  '1': null,
  '2': true
}

• the diff between node 13.x branch and master shows the likely culprit is a new call to _findPath in lib/internal/bootstrap/pre_execution.js, with the values path.resolve(main), null and true -

I patched the line in the local .pnp.js to take that into account, like so:

for (const path of paths || []) {

... and with that the problem seems to be gone.

I could make a PR to change generate-pnp-map-api.tpl.js likewise (and the same in berry, I guess?)

[arcanis]

That would be great! I can't make the fix atm but I can merge it, and you can start using it through yarn set version from sources (v2).

[SimenB]

might be worth considering getting yarn into citgm so these breakages are caught before making it into a node stable release?

[arcanis]

might be worth considering getting yarn into citgm so these breakages are caught before making it into a node stable release?

Yep! I think the v1 is already there but the PnP path isn't covered at the moment. Maybe we could add the v2 and test both versions, since they have significantly different implementations.

On our side we also have our own kind of "Canary in the goldmine" program, but I'm not sure whether Node publishes nightly builds that we could use for this purpose 🤔

[edit] Seems like there is! We should definitely add a test on our side too, then.