[Nix-dev] conflicting packages / priority values

[Roni Choudhury]

>From time to time I see an error message like this:

collision between
‘/nix/store/qs8fq5ld2shc0i3fvbs6n0g0k8fypndm-git-2.13.0/bin/git’ and
‘/nix/store/64fjdb4whkf2r5x8xyqf9kkljnk6w59b-git-2.13.0/bin/git’; use
‘nix-env --set-flag priority NUMBER PKGNAME’ to change the priority of
one of the conflicting packages

I understand what causes it (two packages competing to place the same,
e.g., binaries in my profile), but I’ve never understood how to resolve it.
Usually I just guess priority numbers until it works; more lately I’ve
simply removed the offending package from my environment before repeating
the failing install command. Obviously, neither approach is healthy or
correct :)

The man page for nix-env contains the following:

If there are multiple derivations matching a name in args that have the
same name (e.g., gcc-3.3.6 and gcc-4.1.1), then the derivation with the
highest priority is used. A derivation can define a priority by declaring
the meta.priority attribute. This attribute should be a number, with a
higher value denoting a lower priority. The default priority is 0.

But I’m still not sure what this means for my error situation. How do I
know what the priorities are for the different packages? The default value
is 0, which is the highest priority; what does that mean exactly, for the
default priority to be the highest priority?

Is there a more intuitive way to resolve this sort of conflict? For
instance, is there a way to tell nix-env to force the issue by treating the
requested package as higher priority than any existing ones?

Thanks!

roni
​
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.science.uu.nl/pipermail/nix-dev/attachments/20170616/69164c9c/attachment.html>