Better handling of optional dependencies

[VorpalBlade]

Quoting the readme:

• Packages that are only optional dependencies of other packages must be listed explicitly, otherwise they will be pruned.
• aconfmgr apply removes unlisted packages by unpinning them (setting their install reason as "installed as a dependency"), after which it prunes all orphan packages. If the package is still required by another package, it will remain on the system (until it is no longer required); otherwise, it is removed.

There are two issues with this.

1. An initial save followed by apply is not idempotent if there are any packages in this state.
2. I find it useful to track when a dependency has been installed as a dependency of a package, even if it is only an optional dependency. If I uninstall the package that depends on this optional package pacman -Qtd will tell me about the no longer needed dependency. This only works if the package is not marked as explicit however. Without this, there is a high risk I will forget about the optional dependency and leave it installed.

I propose a new AddPackageAsDependency (or similar, I don't care about the name of it), or perhaps a flag to AddPackage that will allow marking the package as installed as a dependency to satisfy both pacman and aconfmgr

[CyberShadow]

An initial save followed by apply is not idempotent if there are any packages in this state.

Yeah. It's packages which are installed "as dependencies" (--asdeps), but there's nothing actually requiring them. The problem from aconfmgr's side is that it's difficult to calculate the exact set of these packages, taking into account transitivity and things like provides.

I think as a compromise we could make aconfmgr print a warning after save if it detects that there exists at least one package in this state, to mention that the configuration is not yet fully representative of the system state.

I find it useful to track when a dependency has been installed as a dependency of a package, even if it is only an optional dependency. If I uninstall the package that depends on this optional package pacman -Qtd will tell me about the no longer needed dependency. This only works if the package is not marked as explicit however. Without this, there is a high risk I will forget about the optional dependency and leave it installed.

I think this particular problem has a much simpler practical solution: list dependencies of a package right where you have the package itself. Most non-trivial parts of the configuration are going to have additional declarations for things like configuration or ignore files, and dependencies are a part of that. There's no harm in having multiple AddPackage lines for the same package, so dependencies can be repeated for different dependent packages (though it does make it easy to accidentally omit a dependency which should be specified).

See also:

• Allow adding / installing packages with --asdeps #58
• Unrequired packages with dependency cycle not detected #76