Re: GHC 7.8 release?

On 10/02/13 15:36, Simon Peyton-Jones wrote:

We seem to be circling ever closer to consensus here! Yay!

Indeed! Good :-)

However, I’m not getting the bit about API changing vs non-API changing.

Firstly I don’t know which APIs are intended. The GHC API is essentially GHC itself, so it changes daily. Maybe you mean the base package? Or what?

I suspect you mean that a “non-API-changing” release absolutely guarantees to compile any package that compiled with the previous version. If so, that is a very strong constraint indeed. We do observe it for patch releases for GHC (e g 7.6.2 should compile anything that 7.6.1 compiles). But I think it would be difficult to guarantee for anything beyond a patch release. Every single commit (and the commit rate is many/day) would have to be evaluated against this criterion. And if it failed the criterion, it would have to go on a API-breaking HEAD. In effect we’d have two HEADs. I can’t see us sustaining this. And I don’t yet really see why it’s necessary. If you don’t want an API-breaking change, stick with the patch releases.

So, we have a channel for non-API-breaking changes already: the patch releases. So that means we already have all three channels!

Mark is asking for major GHC releases every year at the most, preferably less frequently. That means major GHC releases in the sense that we do them now, where libraries change, and a wave of package updates are required to get everything working. Johan, Manuel and Carter are saying that they want releases that add features but don't break code, i.e. a non-API-breaking release, as a way to get the new bits into the hands of the punters sooner. This is something that we don't do right now, and it would entail a change to our workflow and release schedule. It doesn't mean no API changes at all - we would have to allow APIs to be extended, because many feature additions come with new primops, or new supporting code in the ghc-prim or base packages. The package version policy states precisely what it means to extend an API (http://www.haskell.org/haskellwiki/Package_versioning_policy) and most third-party packages will still work so long as we only bump the minor versions of the packages that come with GHC. The GHC package itself would have to be exempt, because it contains every module in GHC, and hence would be impossible to keep stable if we are modifying the compiler to add new features. Of course it's not practical to maintain an extra branch of GHC for non-API-breaking development - two branches is already plenty. So there would need to be an API-freeze for a while between the major release and the non-API-breaking release, during which time people developing API changes would need to work on branches. Is it workable? I'm not sure, but I think it's worth a try. I wouldn't want to see this replace the patchlevel bugfix releases that we already do, and as Ian points out, there isn't a lot of room in the release schedule for more releases, unless we stretch out the timescales, doing major releases less frequently. Cheers, Simon

·Haskell Platform

·Patch-level releases

·New releases

if that’s so, all we need is better signposting. And I’m all for that!

Have I got this right?

Simon

*From:*Mark Lentczner [mailto:mark.lentczner@gmail.com] *Sent:* 09 February 2013 17:48 *To:* Simon Marlow; Manuel M T Chakravarty; Johan Tibell; Simon Peyton-Jones; Mark Lentczner; andreas.voellmy@gmail.com; Carter Schonwald; kostirya@gmail.com; Edsko de Vries; ghc-devs@haskell.org; glasgow-haskell-users *Subject:* Re: GHC 7.8 release?

We seem to be circling ever closer to consensus here! Yay!

I think the distinction of non-API breaking and API breaking release is very important. Refining SPJ's trifecta:

*Haskell Platform* comes out twice a year. It is based on very stable version of GHC, and intention is that people can just assume things on Hackage work with it. These are named for the year and sequence of the release: 2013.2, 2013.2.1, 2013.4,...

*Non-API breaking releases* can come out as often as desired. However, the version that is current as of mid-Feb. and mid-Aug. will be the ones considered for HP inclusion. By non-API breaking we mean the whole API surface including all the libraries bundled with GHC, as well as the operation of ghc, cabal, ghc-pkg, etc. Additions of features that must be explicitly enabled are okay. Additions of new APIs into existing modules are discouraged: Much code often imports base modules wholesale, and name clashes could easily result. These should never bump the major revision number: 7.4.1, 7.4.2...

*API breaking releases* happen by being released into a separate channel when ready for library owners to look at them. This channel should probably go through several stages: Ready for core package owners to work with, then HP package owners, then all package owners. I'd imagine this is a several month process. At the end of which, the release can go into the main channel. Such a merge shouldn't happen more than once a year... I think even once every two years is fine (!) To avoid confusion, I'd suggest that while in the separate channel, these release be named with odd number: 7.9, 7.11,..., and when moved to the main channel renamed to even: 7.10, 7.12...

This idea of three channels needs to be much more clearly communicated. The warning on the download page is a failure: Googling "ghc" takes you to the home page of GHC which immediately trumpets the "Lastest News" of a release of GHC 7.6.2. Once a user has read that and decided to download, then "STOP!" box is a) going to be skipped as they scan for the download link, and b) if read and followed, causes the "WTF? Why is HP so back rev?" So we need to change the front page so that the three channels are clearly communicated and targeted at the right users.

- Mark

(BTW: The first few links on the GHC web site are out of date: The second nav link is to a survey that is 7 years old. The License page is 8 years out of date. The FAQ is over a year old.)

On Sat, Feb 9, 2013 at 8:24 AM, Ian Lynagh mailto:ian@well-typed.com> wrote:

On Sat, Feb 09, 2013 at 12:06:12PM +0000, Simon Marlow wrote:

...

As a straw man, let's suppose we want to do annual API releases in September, with intermediate non-API releases in February.

That's a non-API release 5 months after the API release.

6.10.2 was 5 months after 6.10.1 (.3 was 1 month later, .4 a further 2) 6.12.2 was 4 months after 6.12.1 (.3 was 2 months later) 7.0.2 was 3.5 months after 7.0.1 (.3 was 1 month later, .4 a further 3) 7.2.2 was 3 months after 7.2.1 7.4.2 was 4 months after 7.4.1 7.6.2 was 4.5 months after 7.6.2

so if we do non-API releases, then perhaps it would make sense to stop doing minor releases (unless a release turns out to just be broken).

Thanks Ian