[arch-dev-public] Library dependencies

Allan McRae allan at archlinux.org
Thu Dec 16 09:53:19 UTC 2021

On 16/12/21 13:24, Xyne via arch-dev-public wrote:
> On 2021-12-15 16:40 +1000
> Allan McRae via arch-dev-public wrote:
>> The dependencies added are purely sonames that the binary are explicitly
>> linked to.  So the binary will be non-function without libraries
>> providing that exact soname.  Thus all these dependencies are necessary.
>> Of course it will be up to the distribution to decide how much they use
>> this feature - should all libraries provide their lib:soname value or
>> just some?  Dependencies are only added if there is a relevant provide.
> What happens if a package includes "optional" binaries that depend on optdeps?
> Do those become hard deps?

Assuming that dependent library is not used elsewhere in the package, 
and the extra library had a provide of its library version, then this 
would add an extra dependency.

There are several options:
1) disable autodeps - these really do not need used everywhere...
2) split the package
3) move the binary into /usr/lib/<pkgname> and add a symlink to 
/usr/bin.  Then (assuming BIN_DIR=usr/bin is the usual search path), the 
dependency would not be added.

Saying that, I am against optional dependencies that are genuinely 
needed for a binary to run.  I think these should be used for features 
that could be dynamically loaded if the optional dependency is present. 
  I prefer package splitting if that is not the case.

>>> 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.
>> I don't see why we can not have multiple packages provide the same
>> command.  We already have multiple packages with the same provides
>> entry, just with a package name and not a command name.
> You can have multiple packages that provide the same command, but there may be
> rare cases where two conflicting packages provide unrelated commands with the
> same name, or a restricted version of a command that may not support the full
> argument set. It's worth considering how to handle such cases now before
> settling on a syntax.

Do you have an example?  I don't like adding complexity for "what if" 
cases that may never occur.

For the case you described, cmd:foo is provided by two packages, foo1 
and foo2.  foo2 has a subset of the functionality.  Then you could 
depend on cmd:foo if either works, or foo1 if you need the full 

>>> 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).
> For optdeps, what I mean is if the normal dependency would be
> "lib:libgpgme.so.11", how will you parse the normal optdep syntax of "pkgname:
> reason"? "lib:libfoo.so.13: required for the command foo". Won't using the same
> delimiter in two different contexts be problematic?

 From memory, the space in "<pkgname>: <reason>" is important for 
optdepends.  I need to check, but I don't think the PKGBUILD linter will 
let PKGBUILDs with optdepends without the space build. And pacman will 
not split the string without it.  So this should be fine.


More information about the arch-dev-public mailing list