ESM importing a CommonJS calls getters

[avaly]

• Version: 14.13.0
• Platform: Linux 5.4.0-52-generic Fix for path.resolve containing relative path to another drive in windows #57~18.04.1-Ubuntu SMP Thu Oct 15 14:04:49 UTC 2020 x86_64 GNU/Linux

What steps will reproduce the bug?

Install pg npm dependency

Run the following module:

import pg from 'pg';

console.log(!!pg);

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

It always reproduces. The imported module needs to be a CommonJS module with getters.

In this case pg exports a getter that lazily tries to load another npm package: https://github.com/brianc/node-postgres/blob/master/packages/pg/lib/index.js#L32-L55

What is the expected behavior?

$ node -v
v14.12.0

$ node pg.mjs 
true

What do you see instead?

$ node -v
v14.13.0

$ node pg.mjs 
Cannot find module 'pg-native'
Require stack:
- /dev/temp/node-bugs/node_modules/pg/lib/native/client.js
- /dev/temp/node-bugs/node_modules/pg/lib/native/index.js
- /dev/temp/node-bugs/node_modules/pg/lib/index.js
true

Additional information

This change was introduced in #35249

[targos]

/cc @guybedford

[guybedford]

So this is by design of the implementation of ES modules in that all named export bindings must be populated upfront and can't be getters themselves. So we do call getters when populating these for the CJS module representation.

On the other hand one option might be to not detect Object.defineProperty cases to make the exports detection less accurate but also less likely to hit cases like this.

In most cases, though surely you would want this to be a named export? Is npm install pg-native to fix really that bad?

I'm also not sure we should be making breaking changes to the named exports algorithm at this stage of the game too.

So I'm somewhat on the fence if we should support this case, but it's worth considering the options.

[avaly]

Is npm install pg-native to fix really that bad?

If it were any other dependency, that wouldn't be an issue. But in this case, this dependency requires build tools to be installed to build a native binary (https://www.npmjs.com/package/pg-native). It's not something one should be forced to do, if we don't plan on using that part of the library.

TBH I would also like to see a change in how the pg library is exporting its native part. So maybe it's not actionable from node.js itself.

But what about other packages that may be using a similar pattern?

[guybedford]

I've posted a fix PR in #35871 for this. I think it does make sense to ignore these exports.

[aduh95]

@avaly Can we close this now? Can you confirm the merged PR fixed your issue?

[avaly]

I've tried just now node-v16.0.0-nightly2020110209af8c822c and it shows the same behavior as 14.13.0

[guybedford]

Thanks for checking this again, created a new PR at #35928.

[guybedford]

Fixed in #35928. Thanks again for the quick reports.