Replace Flow with TypeScript to avoid Facebook’s BSD Patents License

[PatrickJS]

What problem does this feature solve?

Flow in under Facebook’s BSD Patents License and this project was built with it

What does the proposed API look like?

TypeScript which has the Apache License 2.0

[yyx990803]

Flow is used only as a dev dependency, and flow syntax is stripped in the built files, so for end users of Vue (e.g. consuming from NPM) there is nothing related to Flow in the distributed code, which doesn't make them affected by Flow's license in any way.

The only concerning case would probably be someone forking Vue and thus using the source code directly - but even so, flow's own code (governed by its license/patent grant) is not distributed in any way either. I doubt that the mere usage of Flow's syntax is subject to its license.

I think this is a valid concern, but at this moment the logistic costs of migrating can be blocking factor. Maybe someone on the team who are familiar with both Flow/TS can evaluate how much effort that entails.

/cc @HerringtonDarkholme @ktsn @octref

[PatrickJS]

That makes sense. What's interesting is that jsx is under Creative Commons Attribution 4.0 International License while Flow isn't really clear. If Vue.js does end up migrating to TypeScript I can also help with that effort.

[nickmessing]

Considering the fact that typescript team members are interested in Vue (#5887) I would vote for migrating to TypeScript. However, I use flow on day-to-day basics and there is one great feature that I miss in TypeScript (probably more if I do some research). In flow you can use Return type of a function, in TS you cannot.

[HerringtonDarkholme]

HI @gdi2290 , I think @yyx990803 has clear reasoning here. Let me explain some technical issue here.

Migrating to TypeScript is doable, but requires many changes at once.

We cannot use allowJS option in TS, because TS doesn't accept type annotation in JS as flow does. That means we will need to migrate in one single shot, including building system changes.

TS and Flow still have many subtle syntax differences. These differences are small, but ubiquitous. e.g. https://github.com/vuejs/vue/blob/dev/flow/compiler.js#L4 ?string in flow is string | undefined | null in TS.

Other potential issues might be TS/Flow's checking rules. e.g. Flow allows if (o.nonExist) { use(o.nonExist) } while TS does not. I don't know how much code will be impacted until trying to migrate.

[PatrickJS]

I created an issue in Flow and they say it's under Facebook’s BSD+Patents License
facebook/flow#4661

most of the syntax for TypeScript and Flow are similar and in some cases TypeScript allows you to be more strict. If the TypeScript is interested in vue then perhaps vue can request some features in Flow that @nickmessing mentioned

[nickmessing]

@gdi2290, All features I could find are already requested in the issues but looks like TypeScript team is really busy and they need to clear that 2.5k issues backlog :)

[refi64]

Forgive the random outside opinion, but would this really be worth it? Seems like the only benefit would be a potential licensing "problem" that doesn't really affect anything outside of Vue itself...

[nickmessing]

@kirbyfan64, as @HerringtonDarkholme said, it's obviously too much human effort and need to be done during a big code freeze and most probably we don't have that much human effort available, but this is still open for discussion.

[manisenkov]

@yyx990803

...so for end users of Vue (e.g. consuming from NPM) there is nothing related to Flow in the distributed code

Actually whole src folder is distributed with NPM package as it is

vue/package.json

Line 10 in 82f03de

"src",

However, not sure if this could be treated as something Flow-related for the end user.

[LinusBorg]

I would be suprised to find that Facebook has any patent on their type annotation syntax, considering that this has been done before.

And since you are not actively using neither Flow nor the vue source files, you are not using anything flow-related anyway.

[russellr922]

@LinusBorg Flow's license is BSD with Patents, same as React:

The license granted hereunder will terminate, automatically and without notice,
if you (or any of your subsidiaries, corporate affiliates or agents) initiate
directly or indirectly, or take a direct financial interest in, any Patent
Assertion: (i) against Facebook or any of its subsidiaries or corporate
affiliates, (ii) against any party if such Patent Assertion arises in whole or
in part from any software, technology, product or service of Facebook or any of
its subsidiaries or corporate affiliates, or (iii) against any party relating
to the Software. Notwithstanding the foregoing, if Facebook or any of its
subsidiaries or corporate affiliates files a lawsuit alleging patent
infringement against you in the first instance, and you respond by filing a
patent infringement counterclaim in that lawsuit against that party that is
unrelated to the Software, the license granted hereunder will not terminate
under section (i) of this paragraph due to such counterclaim.

Which in my opinion, means that any proprietary product you develop, Facebook can come in and develop the same thing without any fear of lawsuit. Because if you do file suit and you are using Flow (or React or any other BSD+Patent licensed Facebook software on GitHub) your license to use the software terminates, invalidating any proprietary claims you may have had.

TL;DR; yes, I think using the Flow syntax alone does impact Vue.js from a legal standpoint, but I'm not a lawyer, this is just my opinion.

[LinusBorg]

Because if you do file suit and you are using Flow (or React or any other BSD+Patent licensed Facebook software on GitHub) your license to use the software terminates, invalidating any proprietary claims you may have had.

But you are not using Flow, are you? Nothing in Vue's code that you use contains any hint of Flow.

The fact that we (the Vue maintainers) used Flow in our build process to create these files, all while we had/have a licence to Flow, is of no concern to you. You are not using Flow or any of it's patented technologies (if there are any, no one could find applications so far).

Every other interpretation would be crazy, because it would mean that people who do not use the patented technology could get legal problems because of a product they use that was once build with those patents while it was legal. That's crazy. If that's true you should stop writing software alltogether because you can be sued for anything and everything any second.

That would mean that if someone held a patent to something used in webpack, you would have to stop using your already built files because they were once built with webpack while it was still legal.

[russellr922]

@LinusBorg, you may be right, like I said I'm not a lawyer or an expert in law. I just think their licensing goes against the general nature of open source, it's dumb that these types of threads and considerations even need to exist.