--cabal-file needs to go

[ulysses4ever]

As discussed in #6880, --cabal-file has never been used for what people think it's meant. The best way forward, seemingly, is to remove the option (edit by @fgaz: from cabal-install). This follows up on not only #6880 but also #7225.

Alternatives

Different people want different things from --cabal-file, e.g.:

1. Call cabal out of the package directory (Unnecessarily difficult to run executables from outside of project #7940).
2. Call cabal inside of the package directory but with a cabal file located outside of the directory (cabal file not found despite --cabal-file #6880, --cabal-file appears not to work #7225).

The second scenario is not supported currently. The first one can be worked around with another option: --project-file. In particular, you can create a project file along with the package of interest (if there's none currently), and point to it calling cabal from anywhere. In that case the respective package will be built/ran/installed. Beware of a current bug not allowing to use relative paths with --project-file: use absolute path until #7749 (or analogous fix) is merged.

[andreasabel]

Yes, option --cabal-file should be replaced by a --cwd / --directory option as suggested in:

• Option giving the project root directory #8037

Alternatively, it could be fixed to mean these two things (conjunction):

1. Set the project root to the location of the given --cabal-file.
2. Disambiguate in case there are several .cabal files in this directory.

[fgaz]

-1 to giving it some other behaviour, +1 to removing it from cabal-install.

if an option to select a cabal file is needed, we could make packages a valid cli option (#3585).

[andreasabel]

I played a bit with removing the option. It seems to be used in the testsuite. So most work in removing this option would go into restructuring the test that currently use it.
E.g. here are several .cabal files in the same directory, and selected using the --cabal-file option: https://github.com/haskell/cabal/tree/a97e1f13bdb28a3f761d55845f14a9072bee17ca/cabal-testsuite/PackageTests/ReexportedModules/p

[fgaz]

Those look like Setup.hs tests though, so removing the option from cabal-install should be fine

[andreabedini]

I had a go myself here. I am a bit confused (not new 😂). The option --cabal-file is (originally) a Cabal option. The options of Cabal and cabal-install (both v1 and v2 commands) are all jumbled up and this is how it becomes a cabal-install option.

Do we want to remove it from Cabal or only from cabal-install?

AFAIU we do have a mechanism to hide some Cabal flags when we use them from cabal-install. But that's also a bit messed up because it's duplicated in a few places and doesn't really inspire confidence.

Also Cabal's cabalFilePath gets passed to what I understand is the Hooks API (haddockCabalFilePath, hscolourCabalFilePath, copyCabalFilePath, installCabalFilePath, regCabalFilePath, cleanCabalFilePath, ...) and there's some warning in the code about breaking that API.

[fgaz]

From cabal-install. Yes I think we can just hide it

[Mikolaj]

The ticket got closed via the excellent PR by @andreabedini. Is there anything left here to do? If so, maybe let's move it to other tickets with clear scopes?