how to cabal repl?

[jwaldmann]

From the top of this repo, I can do cabal test all, cabal bench set-benchmarks just fine. But:

$ cabal repl containers
Build profile: -w ghc-9.2.5 -O1
In order, the following will be built (use -v for more details):
 - containers-0.6.6 (lib) (ephemeral targets)
Preprocessing library for containers-0.6.6..
GHCi, version 9.2.5: https://www.haskell.org/ghc/  :? for help

<interactive>:1:1: error:
    attempting to use module ‘containers-0.6.6:Prelude’ (src/Prelude.hs) which is not loaded
Error: cabal: repl failed for containers-0.6.6.

There are other ways to fail, e.g.,

$ cabal exec -- ghci containers/src/Data/Set/Internal.hs 
Loaded package environment from /home/waldmann/projekte/containers/dist-newstyle/tmp/environment.-50893/.ghc.environment.x86_64-linux-9.2.5
GHCi, version 9.2.5: https://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Data.Set.Internal ( containers/src/Data/Set/Internal.hs, interpreted )

containers/src/Data/Set/Internal.hs:253:1: error:
    Ambiguous module name ‘Utils.Containers.Internal.StrictPair’:
      it was found in multiple packages:
      containers-0.6.6 containers-tests-0
    |
253 | import Utils.Containers.Internal.StrictPair
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

containers/src/Data/Set/Internal.hs:254:1: error:
    Could not load module ‘Utils.Containers.Internal.PtrEquality’
    it is a hidden module in the package ‘containers-tests-0’
    it is a hidden module in the package ‘containers-0.6.6’
    it is a hidden module in the package ‘containers-0.6.5.1’
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
    |
254 | import Utils.Containers.Internal.PtrEquality
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Failed, no modules loaded.

#893 seems related but it's not merged and when I cherry-pick it, cabal repl still fails like shown above, and:

$ cabal exec -- ghci  containers/src/Data/Set/Internal.hs 
Loaded package environment from /home/waldmann/projekte/containers/dist-newstyle/tmp/environment.-53205/.ghc.environment.x86_64-linux-9.2.5
GHCi, version 9.2.5: https://www.haskell.org/ghc/  :? for help

containers/src/Data/Set/Internal.hs:17:2: error:
     fatal error: containers.h: No such file or directory

I am using

$ cabal --version
cabal-install version 3.8.1.0
compiled using version 3.8.1.0 of the Cabal library 

[treeowl]

I don't know the official way to deal with such issues. There are two things I know work. The permanent solution would rename the internal prelude to something else and import it explicitly everywhere we need it. The other thing I know will sort of work is to cabal repl something else in the repo. Probably the best is to add a new package in the top level directory, make it depend on containers, and add it to the cabal.project file. Using cabal repl on that will let you play with the public interface, but not let you do step debugging and such. So ... we should probably rename the prelude.

[jwaldmann]

public interface ... not debugging

I see. I wanted to call some non-exported functions, so I need to look inside the module. (The work-around is to copy parts of that module to some other place, or in fact develop elsewhere and copy the result back, but that's very inconvenient.)

I was checking https://github.com/haskell/containers/blob/master/CONTRIBUTING.md but it does not mention cabal repl. If there's some progress in the matter, please update that file as well.

[treeowl]

The custom prelude is a new thing we needed to accommodate recent base changes. I didn't notice this issue until a bit later. I'd rather fix it than document it.