Per package/component `cabal clean` (add support for targets)

[michaelpj]

cabal clean is both simple and effective, by virtue of just deleting everything. However, in a multi-package project, I usually want to clean just one package or component that I'm working on.

Of course, the current implementation works for this, but once you accrue a few local packages and a few source-repository-packages, redoing all the work instead of just the last bit becomes painful.

At the moment I work around this by deleting targeted fragments of dist-newstyle/build. This works, but:

• it's clumsy
• it's not discoverable
• it's probably not comprehensively cleaning the package (I have no idea if it gets all the files!)

I think it would be nice to provide a per package/component cabal clean, and hopefully it would just be a matter of listing all the relevant files and deleting them.

[Mikolaj]

I guess we'd need to delete the package or component files and the common files. The trouble is identifying those, in particular if they are not generated with cabal build but only with some other commands or with some specific options.

What does cabal clean do exactly? Only remove dist-newstyle or anything else?

[Mikolaj]

I see there is option

-s, --save-config              Save configuration, only remove build artifacts

I wonder what's 'configuration' and 'artifacts' and if there is anything more. Code-diving would help.

[fendor]

I see there is option

-s, --save-config              Save configuration, only remove build artifacts

I wonder what's 'configuration' and 'artifacts' and if there is anything more. Code-diving would help.

As far as I can tell, that flag is just being ignored, but the code path should delete only dist-newstyle/build which is still not fine-grained enough for the proposed feature.

[Mikolaj]

As far as I can tell, that flag is just being ignored

OK, so we discovered a bug as well.

[fendor]

Looks rather intentional to me:

cabal/cabal-install/src/Distribution/Client/CmdClean.hs

Line 72 in 769e4ed

falseArg

but the commit message itself gives no indication whether it really is intentional

[Mikolaj]

May it be that 'configuration' is only cabal.project.local, which is not removed by cabal clean and that's why cabal clean never removes configuration in the new v2- world? If so, we should mark the -s flag "deprecated; configuration is always saved now" once v1- commands are removed.

However, if 'configuration' is cabal.project.local and artifacts are dist-newstyle/build, is there anything else? E.g., any kind of caches? E.g., when downloading packages form repos?

[fendor]

I think currently cabal clean considers everything in dist-newstyle/build as build artefacts (which makes sense) and other files, e.g. dist-newstyle/cache is configuration.

However, the help message from Setup.hs actually tells us roughly that:

-s --save-configure Do not remove the configuration file (dist/setup-config)
                     during cleaning. Saves need to reconfigure.

Not exactly the same flag but looks similar. Maybe --save-config is a remnant from Setup.hs that doesn't make much sense in cabal v2 world? I would argue at least in that sense.

---

Regarding the issue, I think there are two ways of tackling this:

• Calling Setup.hs clean for each component listed on the command line
• Basically call the functions from Cabal manually (assuming there are no Buildhooks) with the right parameters Just checked, there is a postClean Hook. Only method one remains.

[TeofilC]

As I mentioned on #7857, I'd be interested in trying to implement this.

On the other ticket:

• @gbaz made the good point that when cleaning a component, we want to also clean anything that depends on it.
• @bacchanalia mentioned this overlaps with their work on Better support for running scripts. #7851. So, it seems to me like it would make sense to wait until that's merged to avoid conflicts

[bacchanalia]

@TeofilC #7851 has been merged, so you should be clear if you want to work on this.