🐛 BUG: Cannot use ESM only modules as plugin dependencies

Quick checklist

[X] I am using the latest version of Snowpack and all plugins.

What package manager are you using?

pnpm

What operating system are you using?

Linux (Ubuntu)

Describe the bug

For context, the task I am undertaking is building snowpack-plugin-purescript, a plugin for using Purescript out of the box.

I am unable to use execa@^6 because it the module system built is esm and not cjs.

snowpack@plugin-sass works because it uses execa@^5. https://github.com/withastro/snowpack/blob/c44d86f73ac7b74507d4d5554ccb96e8b7dc5294/plugins/plugin-sass/package.json#L15-L16

execa@^5 contains cjs only, as visible on unpkg.

In the meantime, I can downgrade a major version and pray it works.

Possible Problem

The cli entrypoint loads cjs but never the esm version of the package. https://github.com/withastro/snowpack/blob/c44d86f73ac7b74507d4d5554ccb96e8b7dc5294/snowpack/index.bin.js#L12

I checked the file below and the package.json, and the only reference to the value is this. https://github.com/withastro/snowpack/blob/c44d86f73ac7b74507d4d5554ccb96e8b7dc5294/snowpack/package.json#L28-L35

I can confirm that the esm files are available to be read on my system in node_modules.

Possible Solution

I'm unsure of this, but I feel like we need to check if we're using ESM or CJS and import the CLI using the correct method.

-const cli = require('./lib/cjs/index.js'); 
// More pseudocode than real code as I don't know the exact solution.
+const cli = <is_cjs> ? require('./lib/cjs/index.js'): import('./lib/esm/index.js');

I haven't considered how to structure the package.json file with these changes. I assume to add "module": "./lib/esm/index.js" but there may be more.

Steps to reproduce

~~Posting before my browser turn off, back in a sec.~~

git clone https://github.com/waynevanson/snowpack-esm-dependency-plugin-error.git
cd snowpack-esm-dependency-plugin-error
pnpm install
cd example-application
pnpm snowpack build

Error [ERR_REQUIRE_ESM]: require() of ES Module /home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/example-plugin/index.js from /home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/util.js not supported.
Instead change the require of index.js in /home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/util.js to a dynamic import() which is available in all CommonJS modules.
    at loadPluginFromConfig (/home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/config.js:286:34)
    at /home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/config.js:316:24
    at Array.forEach (<anonymous>)
    at loadPlugins (/home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/config.js:313:20)
    at normalizeConfig (/home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/config.js:435:39)
    at createConfiguration (/home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/config.js:657:30)
    at Object.loadConfiguration (/home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/config.js:735:16)
    at async cli (/home/waynevanson/Documents/code/snowpack-esm-dependency-plugin-error/node_modules/.pnpm/snowpack@3.8.8/node_modules/snowpack/lib/cjs/index.js:145:20)

Link to minimal reproducible example (optional)

https://github.com/waynevanson/snowpack-esm-dependency-plugin-error

Additional Information

I just want to say that I really like how snowpack is unbundled first. It feels very good when mounting directories and it just works.

I have some questions regarding the architecture the plugin API for my use case, but I'll find somewhere else to put that. Thanks again!

FredKSchott / snowpack