Subpath extension patterns and wildcard expansions

[guybedford]

With package exports, it is ambiguous whether users should use extensions, as the author can define whatever they like:

{
  "exports": {
    "./feature.js": "./dist/feature.js",
    "./feature": "./dist/feature.js"
  }
}

as a result it seems likely that packages will have their own preferences here and we might see mixed patterns, unless we want to try and create some wider guidance.

Question: Should we encourage package authors to use extensions or not in subpaths for exports?

Furthermore, when using path exports it means that packages absolutely have to use extensions since:

{
  "exports": {
    "./features/": "./dist/features/"
  }
}

requires each pkg/features/x.js subpath to have an explicit extension.

One might argue that explicitly listing the exports could be an alternative here, but for example I recently provided an exports PR to a package with hundreds of individual components here - carbon-design-system/carbon-web-components#443.

In this case, the package absolutely must require its users to use extensions, and that is the only option practically.

Question: Are we ok with packages therefore having reason to sometimes have users use extensions in subpaths and sometimes not?

One thought here is that if a package wanted to maintain an extensionless interface, we could support this via a wildcard expansion of exports:

{
  "exports": {
    "./features/": "./dist/features/*.js"
  }
}

This would effectively be a sugar for globbing the RHS and treating it as if each entry were a separate entry in exports, but helps when there are hundreds that would be impractical to manually maintain.

When it comes to interop with import maps, the pattern would be that the import map only needs to include those mappings actually in use by the app - just because a component lib has 100s of components, doesn't mean you necessarily need every single one.

The risk is the complexity of users not necessarily knowing the difference beteween path exports and wildcard expansions when it comes to the import map implications.

Question: Would wildcard expansions be a useful feature for encouraging extensionless subpath patterns?

[ljharb]

I don't think we want to encourage directory exports at all, because that drastically expands the API surface for CJS.

For reference, all of my packages omit the extension in "exports" (or will omit it, once they add "exports"), and won't allow any use of extensions to access their internals.

I'm super on board with some way to statically convey "always extensions" or "never extensions" to make import maps, and "exports" boilerplate, smaller - but I would hope whatever we come up with doesn't involve directory exports.

[guybedford]

@ljharb did you see the example PR I linked there? SVG icon and component libraries absolutely have to rely on path exports, which is exactly the main issue at hand for having extension imports.

[guybedford]

Specifically, see for example the icons folder here - https://unpkg.com/browse/carbon-custom-elements@1.1.2/es/icons/, where each folder is explicitly exported separately.

[ljharb]

Sorry, I hadn't clicked through yet. I don't mean to suggest such a setting would be broader than "package level".

Re that specific PR/package, we don't have a better solution than "list every single one explicitly", since the tradeoff for the directory export is pretty large. It seems worth spending time on trying to find a better solution for it than a directory export, and all that entails.

[guybedford]

No problem, just want to be sure we're on the same page with the use case. So the proposal I'm making in this issue is for wildcard expansions:

{
  "exports": {
    "./features/": "./features/*.js"
  }
}

where the * wildcard is like a globbed expansion into separate exports entries internally so that pkg/features/x resolves to features/x.js.

[guybedford]

To give some more examples of the expansion and replacement syntax:

{
  "exports": {
    "./icons/": "./icons/*/index.js",
    "./features/": "./features/*/*.js"
  }
}

would support pkg/icons/x resolving into ./icons/x/index.js and pkg/features/y resolving into ./features/y/y.js.

[bmeck]

I'm very intrigued by templating in these positions. I would need more time to think on it though.

[guybedford]

I've created a PR for this feature in nodejs/node#34718 for further discussion.