[Nix-dev] conflicting packages / priority values

[Roger Qiu]

Yes something like that but without too much fanfare. A standard nix
function encapsulating this aliasing logic and expose it to user space with
nix-env too.

On 17 Jun 2017 16:25, "James Cook" <james.cook at utoronto.ca> wrote:

> Roger, I'm not sure what you're suggesting. Do you mean that the user's
> configuration would explicitly say "include pkgs.someAlternateGitVersion in
> my profile, but rename /bin/git to /bin/gitB"?
>
> As a starting point, I guess you could do that manually by making a new
> expression with a build script like cp -r "$git" "$out"; mv "$out/bin/git"
> "$out/bin/gitB".
>
> On 17 June 2017 at 03:14, Roger Qiu <roger.qiu at matrix.ai> 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> 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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>>>
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