Re: updating many haskell packages

[Federico Beffa <beffa@ieee.org>]

On Sat, Feb 18, 2017 at 6:40 PM, Troy Sankey <sankeytms@gmail.com> wrote:
> Quoting Federico Beffa (2017-02-18 04:43:51)
>> On Fri, Feb 17, 2017 at 6:47 PM, Troy Sankey <sankeytms@gmail.com> wrote:
>> > Forgive me if my understanding of build systems in Guix is flawed, but
>> > let me explain my idea with more detail:
>> >
>> > First, make a data-only package called "ghc-all-cabal-files" containing
>> > the checkout of a specific commit of the all-cabal-files repository from
>> > github.  We can periodically update this package, but there is no
>> > traditional "release"---we just keep pulling the HEAD of the hackage
>> > branch.  This package would then act as a helper package for the haskell
>> > build system---every haskell package should implicitly use this package
>> > as input.  Then we can write a post-unpack phase for the
>> > haskell-build-system which updates the unpacked .cabal file iff it finds
>> > a newer .cabal file in ghc-all-cabal-files (we know how to determine if
>> > the cabal file is newer: it will have a higher "x-revision" value, or
>> > that key will merely exist).
>> >
>> > One problem I have not fully solved is the technical debt associated
>> > with keeping the proposed ghc-all-cabal-files package up-to-date.  I
>> > believe updating it would require all haskell packages to be rebuilt.
>> > We could create a build system argument called use-newest-cabal-file to
>> > toggle the feature, in which case we would only switch it to #t if we
>> > already know the .cabal file to be stale.  Then only a small subset of
>> > packages would need to be rebuilt, and there is less technical debt than
>> > the current solution which involves monkey-patching every cabal file
>> > that needs it.
>>
>> My worry with this approach is that every time that a single cabal
>> file in 'ghc-all-cabal-files' is updated all packages will fail to
>> build (the implicit input will fail). Given that there are several
>> thousands of cabal files, I suspect that this could occur quite often.
>
> Can you elaborate on how all packages will fail to build?

I was thinking that the 'ghc-all-cabal-files' would come from a
released tar file that would change and therefore the hash would not
match.  However, as you mentioned, the package would really come from
a git checkout and would therefore not become unavailable.

My bad, sorry.

Fede