cabal v2-repl broken with head about cabal

[mpickering]

Patch here: #9720

[TeofilC]

@ulysses4ever Here's a standalone reproducer:
Checkout https://github.com/TeofilC/cabal-repl-repro
Then

cabal build foo
cabal repl foo

I think the key detail is having a custom setup somewhere in the project. It seems to be necessary to build first too.

I'm building with GHC 9.4.8.

Adding the following to cabal.project:

allow-newer:
  *:Cabal,
  *:Cabal-syntax

source-repository-package
    type: git
    location: https://github.com/haskell/cabal.git
    subdir: Cabal Cabal-syntax

Makes the issue go away. So it seems like it's an issue with mixing a new cabal with an old Cabal lib?

[ulysses4ever]

I can't reproduce it. What timestamp do you have on that binary? (We really should start embedding commit SHA into the --version info.) Also, what is foo, any chance for a self-contained reproducer?

[Benjamin-McRae-Tracsis]

I ran this command a couple of hours ago: ghcup install cabal --force -u https://github.com/haskell/cabal/releases/download/cabal-head/cabal-head-Linux-x86_64.tar.gz head. The ls timestamp is Feb 14 10:20

[TeofilC]

foo is an arbitrary component in our project. Perhaps there's something peculiar to this project that is triggering it. FWIW cabal build seems to work fine.
I'll extract a reproducer at some point this afternoon.

I was using the latest Linux-static build.

[Benjamin-McRae-Tracsis]

/home/username/.ghcup/bin/cabal-head repl aeson seems to clone a bunch of neccessary stuff and then just exits as described.

[Benjamin-McRae-Tracsis]

running /home/username/.ghcup/bin/cabal-head repl in a non-package environement (just ~) lets me enter the repl:

$ /home/username/.ghcup/bin/cabal-head repl
Warning: this is a debug build of cabal-install with assertions enabled.
Warning: Parsing the index cache failed (Data.Binary.Get.runGet at position
16: Non-matching structured hashes: f46da61e7afa58a5e8fd1d2b6fb79899;
expected: d81bdd513f41b5d7ee4cd28455adadbe). Trying to regenerate the index
cache...
Resolving dependencies...
Build profile: -w ghc-9.4.7 -O1
In order, the following will be built (use -v for more details):
 - fake-package-0 (interactive) (lib) (first run)
Warning: this is a debug build of cabal-install with assertions enabled.
Configuring library for fake-package-0...
Warning: this is a debug build of cabal-install with assertions enabled.
Warning: No exposed modules
GHCi, version 9.4.7: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /tmp/cabal-repl.-239669/setcwd.ghci
ghci> :i head
head :: GHC.Stack.Types.HasCallStack => [a] -> a
        -- Defined in ‘GHC.List’
ghci>

[mpickering]

I am looking into this.

[mpickering]

With 9.6.2 I get:

/home/matt/cabal-bisect/dist-newstyle/build/x86_64-linux/ghc-9.6.2/cabal-install-3.11.0.0/x/cabal/build/cabal/cabal repl foo

with 9.4.8 I get

[matt@nixos:~/cabal-bisect/cabal-repl-repro]$ /home/matt/cabal-bisect/dist-newstyle/build/x86_64-linux/ghc-9.6.2/cabal-install-3.11.0.0/x/cabal/build/cabal/cabal repl foo
Warning: this is a debug build of cabal-install with assertions enabled.
Resolving dependencies...

[mpickering]

Seems that this was broken by the multi-repl patch.

[TeofilC]

Thanks for fixing this so quickly @mpickering !