[Nix-dev] Stackage Support Will Be Discontinued

Teo Klestrup Röijezon teo at nullable.se
Wed Jun 8 21:58:31 CEST 2016

So there will no longer be a way to pin Haskell dependencies? That's a bit
annoying. I can understand the desire to keep security-critical packages
like OpenSSL and user-facing tools like git-annex up to date, but at the
same time there are many non-critical dependencies that I wouldn't want to
go back and patch my one-off deployments for updates of.

The old way is/was certainly not perfect, but at least it provided a
mostly-stable target that I could pretty much forget about after deployment.

On 8 June 2016 at 13:34, Peter Simons <simons at nospf.cryp.to> wrote:

> Fellow Haskell Hackers,
> once the LTS 7.x package set comes out, I intend to make the following
> changes in "master":
>  - All haskell.packages.lts.* package sets will disappear.
>  - haskellPackages will loosely follow the most recent LTS release,
> where "loosely" means that we'll honor the mandated version bounds for
> libraries but tend to ignore them for executables.
> Nixpkgs has shipped every single LTS Haskell version ever released as
> well as an up-to-date copy of the Stackage Nightly package set for the
> last 9 months or so, and during that time we've gained insights that
> suggest this practice is an ineffective use of our resources [1].
> 1. It's pointless to distribute LTS Haskell version x after the release
> of version x+1.
> Stackage does not "maintain" any of its LTS releases. Rather, the
> Stackage volunteers compile a list of package versions, test and verify
> them to the best of their abilities, release that list, and then they
> never touch it again. For example, there won't be any update to LTS
> Haskell 5.4. That update comes in the form of a new package set called
> LTS 5.5. So if LTS 5.4 happens to recommend a package that has a serious
> problem, then that problem will remain there forever. So what is the
> point of distributing LTS 5.4 after the release of 5.5? Apparently,
> Stackage intends LTS 5.5 to *replace* the previous version, so isn't
> that what we should do, too?
> Furthermore, a major release like LTS Haskell 5.x receives no updates
> either after LTS 6.x has comes out, so by the same logic there is no
> point in distributing LTS 5.x after LTS 6.x has become available.
> Contrary to what the name suggests, LTS versions have no guaranteed
> lifetime or support cycle. Stackage does not offer any "long-term
> support" in the sense distributions use the word. "Releases" are merely
> names for tested snapshots of a project that essentially follows a
> rolling release model.
> 2. Following LTS strictly may deprive us of important security updates.
> Whether a package update goes into a minor LTS release or not depends on
> whether that update increments the first or second segment of its
> version number. 6.1.1 -> 6.1.2 will make it, but 6.1.1 -> 6.2 won't.
> That is a pretty good rule based on the assumption that all LTS
> contributors follow it, which -- as you will have guessed -- is not the
> case. The tool git-annex, for example, uses version numbers that have
> only two levels: <api>.<date>. Due to that scheme, git-annex updates
> aren't considered for minor LTS releases, which means that security
> relevant fixes don't reach LTS users until the next major LTS release
> [2].
> 3. Stackage Nightly is not a stable package set.
> Our main package set, haskellPackages, corresponds to Stackage Nightly.
> We made that choice assuming that it would guarantee us a good mixture
> of a stable user experience on one hand and an up-to-date packages on
> the other. Recent experience has shown, however, that Stackage Nightly
> *will* break some of its packages knowingly on the occasion: the Nightly
> package set recently moved to GHC 8.0.1, but a handful of libraries and
> applications blocked that (desirable) update. At that point one would
> expect people to postpone the compiler update, but what happened instead
> is that the troublemakers were simply removed from Stackage [3].
> Now, that is a perfectly legitimate decision to make, it just had the
> unfortunate side effect of breaking all those builds for users of
> Nixpkgs in the process, so arguably following Stackage Nightly with our
> main package set might be a bad idea.
> 4. Stackage does not provide a stable users experience for Nixpkgs.
> Stackage releases come out only after a complete test build of all
> packages has succeeded. Unfortunately, those tests don't always catch
> all issues we might run into, because we compile packages in a different
> environment. Stackage builds on Travis-CI using 64-bit Ubuntu Linux with
> static linking. Our builds run on all kinds of Linuxes and on Darwin, we
> support 32 bit platforms, and we link everything with shared libraries
> by default. This means that some of our builds fail even though they
> succeed in Stackage [4]. Now, we usually report these issues to Stackage
> and on some occasions they've made an effort to fix the issue, but on
> other occasions their response was, essentially, "works for me". That
> leaves us in an odd place, because we're nominally following Stackage
> (and our users rely on getting exactly those builds that Stackage
> promises), but at the same time we have no choice but to deviate from
> Stackage because the builds they want us to do just don't work.
> As such, it's a good idea to use Stackage as a *recommendation* for our
> package set, but we cannot expect to be 100% compliant to Stackage and
> provide a stable user experience at the same time.
> Best regards,
> Peter
> [1] https://github.com/NixOS/nixpkgs/issues/14897
> [2] https://github.com/fpco/stackage/issues/1465
> [3]
> https://github.com/fpco/stackage/commit/cb54d78615c0e154913007e9437ff30de6e13661
> [4] https://github.com/fpco/stackage/issues/1453
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