[arch-dev-public] Library dependencies

[Xyne]

On 2021-12-13 18:35 +1000
Allan McRae via arch-dev-public wrote:

>Hi all,
>
>I submitted a patchset to pacman that I would like some packager 
>feed-back on. [1]
>
>Essentially this replaces the old libdepends/libprovides system into
>something akin to that used by APK.  In short, makepkg.conf will have
>a variable like:
>
>LIB_DIRS=('lib:usr/lib' 'lib32:usr/lib32')
>
>At the end of package building, makepkg will look in the library
>directories and add a provide.  E.g. for pacman:
>
>provide = lib:libalpm.so.13
>
>Note the prefix matches the prefix given to the relevant directory in
>LIB_DIRS.  Similarly, makepkg can add dependencies on libraries. E.g.
>pacman may have:
>
>depends = lib:libgpgme.so.11
>
>Note, to help with bootstrapping this system, or if packages just do
>not want to add libprovides, the depends entries are only added if a
>package actually provides them.
>
>This is different to the APK system for libraries which uses "so" as the
>prefix and is not configurable.  But Alpine used musl, which has no
>concept of multilib, so we need to be a bit more flexible.  Note the 
>"lib" and "lib32" prefixes are just for discussion.  Arch can configure 
>how they want.
>
>The dependency/provides additions can all be disabled in pacman.conf
>with the '!autodeps' option.
>
>Note that APK has similar things for binaries and pkg-config files. e.g.
>provides = cmd:pacman
>provides = pc:libalpm
>
>These can now be readily be added as dropins to libmakepkg.
>
>
>Any opinions on this would be greatly appreciated. Is this a better 
>system than the current one?  Is adding automatic dependencies against 
>the spirit of makepkg where everything is in the PKGBUILD?
>
>Thanks,
>Allan
>
>[1] https://gitlab.archlinux.org/pacman/pacman/-/commits/allan/autodeps

Is it necessary to hard-code LIB_DIRS with prefixes in each PKGBUILD that
provides them? It seems simpler to me to use the standard library paths for the
system with optional overrides in makepkg.conf. Makepkg could then scan those
directories in the pkgdir, check the architecture of any shared objects and
automatically add the prefixed provides (with the prefixes also configurable in
makepkg.conf).

Basically, any shared objects installed to system paths are effectively provided
by the package anyway so they may as well all be included in the array so that
packages can explicitly depend on them as packagers please. Any shared objects
installed elsewhere are effectively invisible except for packages that
specifically look for them in non-standard locations, but then it makes more
sense to have a direct dependency on the package itself, with a version
specification if necessary.

On the depends side, the shared objects used by the package can also be scanned
but it's obviously not as straight-forward to determine whether dependencies
are general, versioned or even optional. A tool could be used to generate a
list or prompt the package interactively to select relevant so deps to add to
the package. Guidelines could be provided by the tool itself to avoid
overspecification. It would be a shame if this led to a permanent dependency
hell of packages depending explicitly on old versions even when not necessary.

As for extending this to other dependency types such as commands, I wonder if
cmd:name would be specific enough. It's rare but sometimes unrelated commands
can have the same name. Some sort of unique identifier may be required. I only
mention it in case it should be considered for generalizing the syntax now
before settling on a final format. Possibly something like
"prefix:identifier/object", where "identifer/" is optional. So you would have
"cmd:unique_cmd" for something unique but "cmd:foo/common_cmd" for some generic
fungible common_cmd provided by different packages when a conflicting
common_cmd exists in another package.

How would this syntax work for optional deps btw? Also, if this is added, it
would be useful to have an option to display the provider package of such deps
in the output of pacman -Qi (e.g. -Qii).