regression in ghc / cabal integration in 9.2.1

Mikolaj Konarski mikolaj at well-typed.com
Sat Oct 30 19:48:11 UTC 2021 

Hi George,

Have you looked at the ticket I gave you? Here's one linked from it
mentioning the topic of ghc-pkg compatibility with v2-install:
https://github.com/haskell/cabal/issues/6508

I'm afraid we don't have any systematic exposition of cabal history
with rationale for its major changes, but there's a changelog and the
commit log. If you'd like to contribute something better, please do.

Why the difference between GHC versions, I don't know, or whether
upgrading your cabal would help (I doubt it). Regarding your workflow,
perhaps ask around or look up in cabal tickets how other people do
this now? I never run ghc directly, so I don't know.

Best,
Mikolaj

On Sat, Oct 30, 2021 at 9:44 PM Brandon Allbery <allbery.b at gmail.com> wrote:
>
> Wasn't there specifically a new cabal version released to deal with
> 9.2.1? 3.4.1.0 / 3.6.2.0?
>
> On Sat, Oct 30, 2021 at 3:24 PM George Colpitts
> <george.colpitts at gmail.com> wrote:
> >
> > Thanks for the quick response Mikolaj. Sorry for the confusion, with cabal install I did use --lib but accidentally omitted that in my original email. In 9.0.1 this results in a successful compilation but in 9.2.1 it does not thus I believe this is a regression.
> >
> > Here's the output I got in 9.2.1:
> >
> > bash-3.2$ cabal install vector --lib
> > Warning: Unknown/unsupported 'ghc' version detected (Cabal 3.4.0.0 supports
> > 'ghc' version < 9.1): /usr/local/bin/ghc is version 9.2.1
> > Warning: Unknown/unsupported 'ghc' version detected (Cabal 3.4.0.0 supports
> > 'ghc' version < 9.1): /usr/local/bin/ghc is version 9.2.1
> > Resolving dependencies...
> > Up to date
> > bash-3.2$ ghc buggc.hs
> > [1 of 1] Compiling Main             ( buggc.hs, buggc.o )
> >
> >
> > buggc.hs:2:1: error:
> >     Could not find module ‘Data.Vector’
> >     Perhaps you meant Data.Functor (from base-4.16.0.0)
> >     Use -v (or `:set -v` in ghci) to see a list of the files searched for.
> >   |
> > 2 | import Data.Vector
> >
> >
> > However I did figure out a workaround: cabal v1-install.
> >
> > As far as I can tell cabal (v2-) install breaks ghc-pkg and compilation. With cabal (v2-) install the workaround for ghc-pkg is to add the option "-f $HOME/.cabal/store/ghc-9.2.1/package.db" to the end of the command "ghc-pkg list". For compilation the workaround is to add "-package-db $HOME/.cabal/store/ghc-9.2.1/package.db" to the ghc-pkg. I don't understand why it was necessary for  cabal v2-install to be incompatible with cabal v1-install. Is there a link to any documentation and justification for these incompatible changes?
> >
> > Thanks again,
> > George
> >
> >
> >
> > On Sat, Oct 30, 2021 at 3:38 PM Mikolaj Konarski <mikolaj at well-typed.com> wrote:
> >>
> >> Hi George,
> >>
> >> Since many versions of cabal, `install` only installs executables, not
> >> libraries, so if that worked for you, you must have had an old version
> >> of cabal.
> >>
> >> Please see https://github.com/haskell/cabal/issues/6481 for some
> >> context and to help you find a new workflow that works for you
> >> (ideally, a standard one).
> >>
> >> Kind regards,
> >> Mikolaj
> >>
> >> On Sat, Oct 30, 2021 at 5:40 PM George Colpitts
> >> <george.colpitts at gmail.com> wrote:
> >> >
> >> > Thanks Ben!
> >> >
> >> > There seems to be a regression in ghc / cabal integration in 9.2.1.
> >> >
> >> > In 9.2.1 if I do
> >> >
> >> > cabal install vector
> >> >
> >> > Compilation of a file containing
> >> >
> >> >
> >> > import Data.Vector
> >> >
> >> >
> >> > main = undefined
> >> >
> >> >
> >> > fails with
> >> >
> >> >  Could not find module ‘Data.Vector’
> >> >     Perhaps you meant Data.Functor (from base-4.16.0.0)
> >> >     Use -v (or `:set -v` in ghci) to see a list of the files searched for.
> >> >   |
> >> > 2 | import Data.Vector
> >> >   | ^^^^^^^^^^^^^^^^^^
> >> >
> >> > The preceding works on ghc 9.0.1
> >> >
> >> > Should I file a bug against Cabal?
> >> >
> >> > Thanks
> >> > George
> >> >
> >> > On Fri, Oct 29, 2021 at 12:54 PM Ben Gamari <ben at well-typed.com> wrote:
> >> >>
> >> >> Hi all,
> >> >>
> >> >> The GHC developers are very happy to at long last announce the
> >> >> availability of GHC 9.2.1. Binary distributions, source distributions,
> >> >> and documentation are available at
> >> >>
> >> >>     https://downloads.haskell.org/ghc/9.2.1
> >> >>
> >> >> GHC 9.2 brings a number of exciting features including:
> >> >>
> >> >>  * A native code generation backend for AArch64, significantly speeding
> >> >>    compilation time on ARM platforms like the Apple M1.
> >> >>
> >> >>  * Many changes in the area of records, including the new
> >> >>    `RecordDotSyntax` and `NoFieldSelectors` language extensions, as well
> >> >>    as Support for `DuplicateRecordFields` with `PatternSynonyms`.
> >> >>
> >> >>  * Introduction of the new `GHC2021` language extension set, giving
> >> >>    users convenient access to a larger set of language extensions which
> >> >>    have been long considered stable.
> >> >>
> >> >>  * Merging of `ghc-exactprint` into the GHC tree, providing
> >> >>    infrastructure for source-to-source program rewriting out-of-the-box.
> >> >>
> >> >>  * Introduction of a `BoxedRep` `RuntimeRep`, allowing for polymorphism
> >> >>    over levity of boxed objects (#17526)
> >> >>
> >> >>  * Implementation of the `UnliftedDataTypes` extension, allowing users
> >> >>    to define types which do not admit lazy evaluation ([proposal])
> >> >>
> >> >>  * The new [`-hi` profiling] mechanism which provides significantly
> >> >>    improved insight into thunk leaks.
> >> >>
> >> >>  * Support for the `ghc-debug` out-of-process heap inspection library
> >> >>    [ghc-debug]
> >> >>
> >> >>  * Significant improvements in the bytecode interpreter, allowing more
> >> >>    programs to be efficently run in GHCi and Template Haskell splices.
> >> >>
> >> >>  * Support for profiling of pinned objects with the cost-centre profiler
> >> >>    (#7275)
> >> >>
> >> >>  * Faster compilation and a smaller memory footprint
> >> >>
> >> >>  * Introduction of Haddock documentation support in TemplateHaskell (#5467)
> >> >>
> >> >> Finally, thank you to Microsoft Research, GitHub, IOHK, the Zw3rk stake
> >> >> pool, Tweag I/O, Serokell, Equinix, SimSpace, and other anonymous
> >> >> contributors whose on-going financial and in-kind support has
> >> >> facilitated GHC maintenance and release management over the years.
> >> >> Moreover, this release would not have been possible without the hundreds
> >> >> of open-source contributors whose work comprise this release.
> >> >>
> >> >> As always, do open a [ticket] if you see anything amiss.
> >> >>
> >> >> Happy testing,
> >> >>
> >> >> - Ben
> >> >>
> >> >>
> >> >> [apple-m1]: https://www.haskell.org/ghc/blog/20210309-apple-m1-story.html
> >> >> [proposal]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0265-unlifted-datatypes.rst
> >> >> [-hi profiling]: https://well-typed.com/blog/2021/01/first-look-at-hi-profiling-mode/
> >> >> [ghc-debug]: http://ghc.gitlab.haskell.org/ghc-debug/
> >> >> [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new
> >> >> _______________________________________________
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>
>
> --
> brandon s allbery kf8nh
> allbery.b at gmail.com

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