Workaround for DEP0148: Use of deprecated folder mapping "./" in the "exports" field

[ai]

• Version: 16.0
• Platform: Linux foxbat 5.11.15-200.fc33.x86_64 deps: update openssl to 1.0.1j #1 SMP Fri Apr 16 13:41:20 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

What steps will reproduce the bug?

npm i postcss
echo "let list = require('postcss/lib/list')" > index.js
node index.js

The output:

(node:12793) [DEP0148] DeprecationWarning: Use of deprecated folder mapping "./" in the "exports" field module resolution of the package at /home/ai/test-cjs/node_modules/postcss/package.json.
Update this package.json to use a subpath pattern like "./*".

But replacing exports in PostCSS’s package.json to "./*": "./*.js" will break old Node.js.

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

Always

What is the expected behavior?

1. Not show deprecation warning until we have active Node.js without * support.
2. Suggest a solution to support both syntaxes.

Additional information

postcss/postcss#1561

The warning was disabled in Node.js 15.

[aduh95]

@nodejs/modules

[ljharb]

There is no easy workaround. Your only choices are:

1. make a breaking change for older node versions
2. ignore the warning in order to retain compatibility
3. explicitly enumerate every possible specifier that old node users depend on. https://npmjs.com/ls-exports can help with this (use --json to see details)

[ai]

@ljharb

make a breaking change for older node versions

By the way, what Node.js versions does not support * in exports?

[ljharb]

https://www.npmjs.com/package/has-package-exports is where i keep track of that; which says v14.18+.

[ai]

Should we remove this warning from Node.js for node_modules again until Node.js 12 EOL?

[ljharb]

It was very intentional, as i recall, to include the warning, despite putting module authors in this unfortunate position.

[aduh95]

Support for "exports" patterns is in v12.20.0 and v14.13.0+

node/doc/api/packages.md

Lines 8 to 11 in 8780537

	- v14.13.0
	- v12.20.0
	pr-url: https://github.com/nodejs/node/pull/34718
	description: Add support for `"exports"` patterns.

[ljharb]

@aduh95 ha, thanks, turns out i updated my repo but didn’t publish a new version 🤦

[ai]

I fixed PostCSS by manually listed all exported files.

[MylesBorins]

@ai a work around is to export "./*" first and then "./" after, older versions of node will ignore the "/*" as an invalid path and newer versions of node will match early and never hit the deprecated folder export pattern. So for post-css I believe you should be able to do something like the below instead of explicitly exporting everything and it will work consistently without errors across node.js ESM implementations in 12 / 14 / 15 / 16

  "exports": {
    ".": {
      "require": "./lib/postcss.js",
      "import": "./lib/postcss.mjs",
      "types": "./lib/postcss.d.ts"
    },
    "./package.json": "./package.json",
    "./*": "./*",
    "./": "./"
  },

[ai]

Thanks. We can close if we do not want to improve docs.