cabal-clean : Remove superseded artefacts of cabal v2-build

Removes compilation artefacts in dist-newstyle/build from older versions of the package or superseded minor versions of GHC.

For the impatient

Installation

cabal install cabal-clean

Run

cd $MY_PROJECT
cabal-clean

This lists the build artifacts under dist-newstyle/build.

---	191M	dist-newstyle/build/x86_64-osx/ghc-7.10.3/$MY_PROJECT-2.9.2
---	 72M	dist-newstyle/build/x86_64-osx/ghc-8.10.4/$MY_PROJECT-2.9.2
---	162M	dist-newstyle/build/x86_64-osx/ghc-9.0.1/$MY_PROJECT-2.9.2
+++	135M	dist-newstyle/build/x86_64-osx/ghc-7.10.3/$MY_PROJECT-2.9.3
---	 70M	dist-newstyle/build/x86_64-osx/ghc-8.10.4/$MY_PROJECT-2.9.3
+++	145M	dist-newstyle/build/x86_64-osx/ghc-8.10.5/$MY_PROJECT-2.9.3
+++	159M	dist-newstyle/build/x86_64-osx/ghc-9.0.1/$MY_PROJECT-2.9.3

The superseded ones, printed in red and prefixed by dashes (---), can then be removed by:

cabal-clean --delete

Rationale

v2-cabal (the nix-based cabal) maintains a directory structure for local builds of the form dist-newstyle/build/$ARCH/$HC/$PACKAGE-$VERSION (plus other stuff that does not take up much disk space). During active development with several $HC versions and $VERSION bumps for the $PACKAGE, lots of out-dated build artefacts accumulate over time.

A simple way to clean up is removing the whole dist-newstyle folder, but one might want to keep the build artefacts of the most recent package $VERSIONs of the most recent versions of the Haskell compiler ($HC).

Philosophy

• Go for saving the most disk space with the simplest approach, rather than a complete clean-up. E.g., don't care about outdated contents in dist-newstyle/package-db as they take little space.

• Keep only the most recent $VERSION of the package.

• Keep only the most recent major versions of $HC.

• Assume a monopoly of GHC, ignoring other Haskell compilers, so only treat $HCs of the form ghc-$GHCVER.

• Work autonomously, ignoring cabal files. This saves us parsing various home-grown cabal file formats. The latter could be easy using the Cabal package, but this package is not very stable, and we shy the maintenance effort of depending on Cabal.

• Dry-run is the default, giving the user opportunity to review the clean-up plan.

Functionality

• Read the contents of dist-newstyle/build, organizing them into a tree according to the pattern $ARCH/ghc-$GHCVER/$PACKAGE-$VERSION.

• Display the outdated versions.

  Try to get the disk usage with du -h and display it. (I could not find a Haskell library that gets the disk usage OS-agnostically.)

• With option --delete actually remove the respective folders.

Examples

List build artifacts of current project, marking superseded ones that can be deleted:

cabal-clean

Actually delete superseded builds:

cabal-clean --delete

Delete superseded builds without changing to directory:

cabal-clean --delete path/to/my/project/dist-newstyle

Delete superseded builds in many projects:

find . -name "dist-newstyle" -exec cabal-clean --delete {} \;

Get help:

cabal-clean --help

Related

cabal v2-clean (as of 2021-08-16)

• Removes all build artefacts.
• Does not have a --dry-run preview.