CS2 Discussion: Project: CoffeeScript 2.0.0

[GeoffreyBooth]

Branching off from #34, this is a place to discuss a potential 2.0.0 release of CoffeeScript. The proposed 2.0.0 release will include breaking changes, and have two major features:

• Classes output with the class keyword. See CS2 Discussion: Output: Classes #22.
• ESNext output whenever possible, with all ES5 or ES3 shims removed.

I think we should release 2.0.0-alpha1 as soon as classes are ready. We would also add a note on coffeescript.org that 2.0.0 is in alpha and subject to further breaking changes, which would be released as 2.0.0-alpha2 and so on until we’re pretty sure we have no further breaking changes for the 2.x major version.

The other features on our list that aren’t breaking changes (tagged template literals, await) can be released either on the 1.x branch or the 2.0.0-alpha branch. They should be implemented only as ESNext output, regardless of branch.

We should try to define exactly which features will have their output changed to ESNext. Here and here are comparisons of CoffeeScript features to new ES2015 features. Here is a pretty concise list of features introduced by ES2015. I’ve started a GitHub project where we can put cards into columns to define what features we want to update.

The other big issue is what to do about const/let and block scoping. Let’s please hash out an approach to that one over in #35, to not overwhelm this thread. Also if we can, let’s please keep discussion of whether we want to refactor or replace the compiler over in #25.

EDIT 2016-09-19: Changed “beta” to “alpha”.

[GeoffreyBooth]

Also in 2.0.0 would we get rid of the top-level function safety wrapper? It’s already disabled for any file with an import and export statement, should we just get rid of it altogether?

EDIT: branched off as #38

[mrmowgli]

The top level safety wrapper is actually useful in certain situations, although I admit I personally haven't used it in quite a while. Perhaps as another issue and a poll? Also Github just added the Projects tab, any interest in using that for this project?

[GeoffreyBooth]

@mrmowgli Sure: https://github.com/coffeescript6/discuss/projects/1

[lydell]

I like the proposed release scheme of 2.0.0-beta1, 2.0.0-beta2, etc. I also like the idea of adding non-breaking changes to 1.x. 👍 from me.

[jashkenas]

Sounds fine to me, but speaking generally "beta" implies feature-completion that still needs bugfixing. Instead, call it "alpha".

2.0.0-alpha1, 2.0.0-alpha2 etc. When the major ES6 breaking changes have been made, then you can go beta.

[GeoffreyBooth]

Sounds good to me. Okay, I’ll treat this as our plan for moving forward.

[GeoffreyBooth]

Should we start this work in a 2.0.0 branch or start accepting breaking-change pull requests into master? If we do master, then there’s no possibility of more 1.x releases. I’m thinking we probably want to retain the ability for 1.x releases, at least to address any bugs people find in the modules code.

As part of 2.0.0 I think we should also prioritize clearing out the backlog of open pull requests on coffeescript.org; especially the ones that only affect downstream tools, like fixing location data. I suspect that those have been ignored because they have no effect on the CoffeeScript compiler and could introduce bugs or breaking changes . . . but 2.0.0 might be the place to deal with that. These fixes will probably end up helping us farther down the road if we implement a new compiler.

[jashkenas]

To avoid breaking people unnecessarily, let's leave master as the branch for the "next stable release" — meaning that it stays 1.X for now. Work on and release from a 2 or 2.0.0 branch, and it can become "master" once it stabilizes.