add @parcel/transformer-reason

[abdullahtariq1171]

↪️ Pull Request

This PR tries to add reason plugin for transforms. Fixes #3359

Todo:

• Compiling Reason to JavaScript with bsb-js
• Collecting dependencies as included files so Parcel watches them (Parcel 1 does not currently do this properly)

💻 Examples

🚨 Test instructions

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

[abdullahtariq1171]

I'm not exactly sure how gonna collect dependencies as included files, any help would be very useful.

[mischnic]

I have no experience with bucklescript, but the bsb-js was last updated one year ago.
The official docs talk about bs-platform (https://bucklescript.github.io/docs/en/installation) and to not use an integration with a bundler 😕 (https://bucklescript.github.io/docs/en/interop-with-js-build-systems#popular-js-build-systems)

[abdullahtariq1171]

yes, bsb-js is just a wrapper on top of bs-platform. here is source code of 'bsb-js'

I've thinking about this, we can detect the dependencies using regex but since we use bsb-js, and it doesn't return any information. So how are we going to actually collect these dependencies?

cc: @devongovett

---

Also here is previous discussion #342, might be helpful some questions.

[gugahoa]

Hi all, maybe this PR could take inspiration from the new react-hooks template for bsb found here: https://github.com/BuckleScript/bucklescript/blob/3fe3e854f8a0d31691d396e5a41e728f58f2f6cd/jscomp/bsb/templates/react-hooks/watcher.js

It shows how to do a simply watcher.

[DeMoorJasper]

@gugahoa it's more than just watching we need to know all the files that are being compiled/bundled for cache invalidation as well. Unless we simply disable cache for reason, but that's not really optimal.

[gugahoa]

@DeMoorJasper What would be the impact of disabling cache for reason?

[DeMoorJasper]

@gugahoa it would be a lot slower to build reason

_{Sent with GitHawk}

[mischnic]

bsb seems to generate a file listing all dependencies of a source file: https://bucklescript.github.io/docs/en/interop-with-js-build-systems#getting-projects-dependencies

But you need to explicitly specify source folders in the bsconfig.json file. bsb really doesn't want to be integrated into another build system.

[gugahoa]

@mischnic @DeMoorJasper
So in simple terms, a good enough reason plugin would:

• Run bsb in watch mode with websocket
• Listen to websocket to be notified on change
• On notifiy, (somehow) discover the changed file
• Find the .mlast.d of that file and invalidate those files

Is that it?

[DeMoorJasper]

@abdullahtariq1171 could you update this PR to be more complete as requested?

[abdullahtariq1171]

hey guys I'm sorry I won't be able to work on this. Anyone want's to grab this from here would be welcomed.