Strip flow types

[Kronuz]

Babel has this module: @babel/plugin-transform-flow-strip-types, which simply ignores flow types. There are quite a few modules out there that use babel to compile, yet have flow typing.

Please add support for stripping types, no need for full Flow support (issue #174), just ignore/strip them.

[kdy1]

Closing as flow decided to focus on internal usages.

[FezVrasta]

That doesn't mean external projects can't use it. There are a lot of projects that still use Flow.

[kdy1]

@FezVrasta If you send a PR, I'll happily accept it and maintain it.

[kdy1]

@FezVrasta Maybe it's unrelated question, can you show me some projects using flow?
I've been working on swc for few years and I didn't have time to look at the source code of other js/ts projects.

[FezVrasta]

I maintain Popper, which is used by approximately a couple million websites around the world, and it's entirely wrote with Flow.

https://popper.js.org

[FezVrasta]

@FezVrasta If you send a PR, I'll happily accept it and maintain it.

The best way to implement it would be to use flow-remove-types since it's a standalone binary (no Babel involved) and it's maintained by the Flow core team.

This is an example of how to use it programmatically with JavaScript:

https://github.com/leebyron/rollup-plugin-flow/blob/master/index.js

I'd be happy to send a PR, I just need to understand if integrating flow-remove-types would be an acceptable approach, and some guidance on where to start.

[kdy1]

Hmm... I don't think using js module is acceptable.
I'll just try implementing it in rust when I have some free time. (Hopefully tomorrow, as it's holiday)

[FezVrasta]

Thanks that'd be awesome! The whole Flow community will be grateful for this 🤗

[kdy1]

I found that I have a task with higher priority, so I'm postponing this.

[kdy1]

I looked at the source code of flow-remove-types, and it depends on flow-parser, which means lots of jobs.

[FezVrasta]

Yes it depends on the JS-compiled OCaml compiler. Considering how fast the OCaml compiler it is I wonder if swc could directly interface with it?

TBH a simple plugin-like approach where each file is feeded through the Flow parser would be all it's needed to address this.

[kdy1]

Is there a way to see the size of the compiled flow stripper?
I don't want to bloat the binary size.

[FezVrasta]

It's between 30-40 MB depending by the target platform:

From my understanding, the Babel plugin to strip Flow types doesn't depend on the Flow compiler though, so maybe you could use their source code as reference for a Rust implementation?

https://github.com/babel/babel/blob/master/packages/babel-plugin-transform-flow-strip-types/src/index.js

[kdy1]

From my understanding, the Babel plugin to strip Flow types doesn't depend on the Flow compiler though, so maybe you could use their source code as reference for a Rust implementation?

Yes. But it means lots of work. It's really enormous amount of work.

[FezVrasta]

From my understanding, the Babel plugin to strip Flow types doesn't depend on the Flow compiler though, so maybe you could use their source code as reference for a Rust implementation?

Yes. But it means lots of work. It's really enormous amount of work.

What about the approach I described above?

TBH a simple plugin-like approach where each file is feeded through the Flow parser would be all it's needed to address this.

[kdy1]

I'm fine with it.
But currently, there's no plugin api for parser, so we need to make some decisions about the api.

[FezVrasta]

Ok that sounds great, this way the Flow support will be implementable at plugin level and the core is not tied to it.

Is there anything else I can do to help to move this effort forward? Do you have an RFC or other kind of documentation where the API is being designed?

[kdy1]

Can you join discord server at https://discord.gg/GnHbXTdZz6 ?

I'm not sure about the RFC, but I think people in discord server may provide some ideas about the api.

[FezVrasta]

For anyone interested, I started a conversation here https://discord.com/channels/889779439272075314/889780921002246154/894551464410763314

[noppa]

Facebook's Hermes project also has parsers for both TypeScript and Flow, written in C++, if that's any help.

[FezVrasta]

Facebook's Hermes project also has parsers for both TypeScript and Flow, written in C++, if that's any help.

That's great! It also seems to expose a Rust API?

[mikeduminy]

react-native also uses flow which need to be stripped away in production builds

[langri-sha]

Shooting from the hip: there's only a few differences between the TS and Flow type syntaxes, so perhaps it's possible to reuse a goodly portion of the TS transformer and take it from there?

[kwonoj]

I'm going to suggest to close this. /cc @kdy1 before actually closing it.

Given the scope of the SWC's feature and codebase, I don't think we have enough bandwidth to support this continuously. Probably the best way forward is someone making a userland parser based on the existing implementation of SWC.

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.