[Discuss] Standardize alias support

[FredKSchott]

Background

Currently, we support two kinds of import aliases:

• Package: {"react": "preact/compat"}
• Directory: {"@app": "./src"}

We have had requests for several improvements to this system:

• Inner-Package Files/Assets: support to alias assets in node_modules #801 {"fasvgs": "@fortawesome/fontawesome-free/svgs"}
• File: Using flow with snowpack #877 {"confetti": ./local/confetti.js"}
• URL: `alias` does not support URLs #878 {"confetti": "https://cdn.skypack.dev/canvas-confetti"}

Todo

What do we support? What do we not support? Let's come up with an answer, document it, and get proper error messages.

[FredKSchott]

Here's where I land:

🟥 Inner-Package Files/Assets: This feels like the least useful to me, considering we already support aliasing to the package itself. In the example above, you're only saving a few characters vs. the already supported {"fasvgs": "@fortawesome/fontawesome-free"}

✅ File: If we already support aliasing to a directory, this feels like something that we should also support and it feels like a strange line to draw that you can import directories but not files. I also hope that It wouldn't be too difficult to implement.

🟨 URL: This is one that I literally cannot wait to support conceptually (import 'foo', and it actually imports from our CDN) but I just don't think that this config is the right place for it. We experimented with support for a top-level Snowpack import map earlier this year, I'd rather bring that back and offer this support via import map.

[thezimmee]

Related question... I'm trying to install a package with snowpack that lives outside/"above" the main directory. Is this currently possible? This would be especially useful in a monorepo. For example, say I have a monorepo at monorepo/root and a child package which uses snowpack at monorepo/root/packages/snowpackPackage. Can I do something this:

module.exports = {
  alias: {
    'my-other-package': '../my-other-package'
  }
}

or some variation to get access to my-other-package in monorepo/root/packages/my-otherpackage?

I appreciate your help. And I absolutely love Snowpack.

[FredKSchott]

I think that it is possible, actually. Right now we do: path.resolve(cwd, replacement) which should support a replacement value that starts with ../

[thezimmee]

That would be wonderful. I feel like I tried that already, but I will double check when I transition back to snowpack and raise again if it didn't work. Thank you!

[donmccurdy]

I'm not sure which case this falls under, if any, but in trying to use Snowpack for local demos in the directory for a library (not an application) I'd like to be able to alias my own library, so the demo uses the same imports that my users would need. For example:

Project structure:

• build/my-library.min.js
• src/my-library.js
• packages/subpackage.js
• package.json (defines module: 'build/my-library.min.js')

<!-- demo.html -->
<script type="module">
  import { MyLibrary } from 'my-library';
  import { MySubpackage } from 'my-library/packages/subpackage.js';
</script>

Using this alias...

{
  "alias": {
  	"my-library": "./"
  }
}

... correctly loads subpackage.js, but doesn't resolve the bare identifier's path from package.json. Instead, it tries to look up /my-library.js, which doesn't exist. Do you think this would be covered under any of the ideas here?

[donmccurdy]

As a more concrete suggestion, having "alias" support syntax compatible with the import map specification might be a good goal. I think the "Packages" via trailing slashes section there would solve the case I mentioned above.

[kylecombes]

It might also be nice to support an aliasing config option similar compilerOptions.baseUrl in TypeScript. If compilerOptions.baseUrl == "src" in tsconfig.json, you can import src/module_a/utils.ts using import * as utils from 'module_a/utils'.