[Nix-dev] conflicting packages / priority values

[Layus]

When you get too many such conflicts, you are probably looking for 
virtual environments.
These are provided by nix-shell, and allow to temporarilly override the 
set of available, installed applications.

Looking at your example, a clash between two different git's at the same 
version is very weird...

-- Layus.

On 17/06/17 05:14, Roger Qiu wrote:
> I wonder in other programming languages, name clashes are usually 
> resolved through aliasing. Would it be possible for nix to install 
> packages while aliasing their outputs to a different name to avoid 
> clashes like this?
>
> On 17 Jun 2017 09:07, "Roni Choudhury" <aichoudh at gmail.com 
> <mailto:aichoudh at gmail.com>> wrote:
>
>     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
>
>     ​
>
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