The name is probably quite self-explanatory. As pacman unfortunately does not ship with an easy method of intelligent cleaning the package cache, this program tries to compensate for it. Package cache comes in very handy if a system upgrade breaks something and there comes a need to revert some or all of the upgraded packages to their previous versions. On the other hand, just left as is, the package cache grows over time and consumes more and more disk space.
This automatic cleaner takes the simplest approach except, perhaps, for
mindlessly deleting the whole cache. It lists the package cache directory
(/var/cache/pacman/pkg) for all package files, groups them by package
they belong to and for each package keeps the most recent version and
deletes the rest.
Determining the version from the file name is quite tricky, because not all packages are versioned by semver; in some cases hashes are used, which cannot be reasonably compared. Therefore, rather than parse versions from filenames, this program simply looks at files' creation time, assuming that the most recently created file is also the most recent version (which should always be true unless user creates files in the cache directory manually).
$ cargo build --release
$ sudo cp target/release/pacman-cache-clean /usr/local/bin
Of course any other location in $PATH will do just as well.
As of now the program does not take any arguments or configuration. Simply run the binary. Don't forget to give it permission to write to the package cache directory (which usually boils down to running the program as root).
The program will print out each file name it deletes. If the output is clean, no packages were deleted at all.