Add pnpm, yarn & bun support

[andershagbard]

This PR makes the action use the package manager defined by the repository. If the package isn't available for the runner, it will fall back to npm.

@charlespwd comment

• figure out why pnpm doesn't like --no-lockfile (or figure out the proper flag that lets you install without lockfile changes)

Not sure if this was incorrect. Does this action output errors in the job log?

• consider making a global install (?)

Kept it as local install in this PR.

Tested with

• pnpm
• npm
• yarn
• bun

Resolves #37

[charlespwd]

Are we sure this works on Windows runners? Didn't see a comment about it in the README

[charlespwd]

nvm looks like it does:
https://github.com/npm/node-which/blob/main/lib/index.js#L4

[charlespwd]

Not sure if this was incorrect. Does this action output errors in the job log?

I didn't test this, I only saw that in the logs from the report and it looked sus. Haven't played with pnpm yet, never felt the need to upgrade tbh (and every time I see a pnpm related issue, it feels like a waste of time 😅. I see a whole lot more of those than yarn.)

[andershagbard]

I don't think that WARN is an error. Seems to work fine with pnpm.

[andershagbard]

@charlespwd What is the status on this?

Running npm install @shopify/cli after you already run pnpm install is very time consuming.

This is my action with pnpm install:

This is my action without running pnpm install:

Notice Theme Check is 4x slower.

I do this because I am compiling JS and CSS. Theme Check will return errors for MissingAsset if I don't.