Fwd: Release policies

[Michael Snoyman]

On Fri, Dec 15, 2017, 6:23 PM Simon Peyton Jones <simonpj at microsoft.com>
wrote:

> Therefore bytestring, process, containers, transformers, and many more
> will be pinned in a Stackage snapshot.
>
> So that would make it significantly harder, even impossible, for GHC
> releases to make any promises about the .cabal-file format of these
> packages, wouldn’t it?
>
>
>
> So even if we made some back-compat promise for non-reinstallable things
> like integer-gmp or base, we could not do so for bytestring.
>
>
>
> Does that give you cause for concern?   After all, it’s where Trac #14558
> started.  I don’t see how we can avoid the original problem, since we don’t
> have control over the .cabal file format used by the authors of the
> packages on which we depend.
>
>
>
> Still: GHC can only depend on a package P if the version X of Cabal that
> GHC is using can parse P.cabal.  So if we fix Cabal-X some while in advance
> and announce that, perhaps that would serve the purpose?
>
>
>
> Simon
>
>
>
That will certainly help. Even if GHC can't force any behavior on upstream
packages, perhaps just an official request that new features in the cabal
file format be held off on would be sufficient. After all, the case in the
Trac issue was a situation where the new cabal feature want necessary. I
would imagine that in the vast majority of cases, maintaining backwards
compatibility in these packages will not only be desirable, but relatively
trivial.


*From:* Michael Snoyman [mailto:michael at snoyman.com]
> *Sent:* 15 December 2017 09:27
>
>
> *To:* Simon Peyton Jones <simonpj at microsoft.com>
>
> *Cc:* Boespflug, Mathieu <m at tweag.io>; Ben Gamari <ben at well-typed.com>;
> ghc-devs <ghc-devs at haskell.org>
>
>
> *Subject:* Re: Fwd: Release policies
>
>
>
>
>
>
>
> On Fri, Dec 15, 2017 at 12:10 PM, Simon Peyton Jones via ghc-devs <
> ghc-devs at haskell.org> wrote:
>
> |  at this point in time Stackage works
> |  hard to ensure that in any given package set, there is *exactly one*
> |  version of any package. That's why Stackage aligns versions of core
> |  packages to whatever ships with the GHC version the package set is
> |  based on.
>
> Ah. It follows that if Stackage wants to find a set of packages compatible
> with GHC-X, then it must pick precisely the version of bytestring that
> GHC-X depends on.  (I'm assuming here that GHC-X fixes a particular
> version, even though bytestring is reinstallable?  Certainly, a
> /distribution/ of GHC-X will do so.)
>
> If meanwhile the bytestring author has decided to use a newer version of
> .cabal file syntax, then GHC-X is stuck with that.  Or would have to go
> back to an earlier version of bytestring, for which there might be material
> disadvantages.
>
> That would make it hard to GHC to guarantee to downstream tools that it
> doesn't depend on any packages whose .cabal files use new syntax; which is
> where this thread started.
>
> Hmm.  I wonder if I have understood this correctly.  Perhaps Michael would
> like to comment?
>
>
>
> Stackage does in fact pin snapshots down to precisely one version of each
> package. And in the case of non-reinstallable packages, it ensures that
> those package's transitive dependency set are pinned to the same version
> that ships with GHC. I know there's work around making more package
> reinstallable, and the ghc package itself may have crossed that line now,
> but for the moment Stackage assumes that the ghc package and all its
> dependencies are non-reinstallable. Therefore bytestring, process,
> containers, transformers, and many more will be pinned in a Stackage
> snapshot.
>
>
>
> Michael
>
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