Re: regression in ghc / cabal integration in 9.2.1

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 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 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 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 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 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-un... [-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 _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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-- brandon s allbery kf8nh allbery.b@gmail.com