Prioritize BuildRequires from Copr

In this short article, we are going to see how it is possible to prioritize external repositories when building a package in Copr.

Imagine the following use-case. You have a package foo which depends on package bar, i.e., BuildRequires: bar. The package bar is provided by Fedora repositories in version 1.2, and you have also built the package in version 1.1 in Copr. Now you want to build foo and explicitly say, that package bar should be installed from your Copr project, even though it is a lesser version than Fedora provides.

Solution

We have extended the syntax for enabling external Copr repositories to support this feature. For a long time, it has been possible to write them this way.

copr://<owner>/<project>

Now you can also specify the priority like this:

copr://<owner>/<project>?priority=<num>
copr://frostyx/copr-dev?priority=10

Please note that other parameters than ?priority are currently ignored.

https://foo.bar/baz?priority=90

DNF

How does it work internally? What priority number should you set? The user-specified value is passed to a repo definition and then it is up to the DNF to properly resolve dependencies. Please see man dnf.conf for the details.

priority
      integer

      The priority value of this repository, default is 99. If there is more than one candidate
      package for a  particular  operation,  the one  from  a  repo with the lowest priority value
      is picked, possibly despite being less convenient otherwise (e.g. by being a lower version).