Idea: Ability to define dependencies between coprs (correctly)

[Honza Horak]

Hi all,

I have a proposal that would change how dependencies are defined in copr:

Problem:
Currently, copr allows to add a link to an arbitrary repo URL that is 
available for installing dependencies during building in copr. Using 
this dependent repo link we are able to build packages in coprA with 
dependencies in another coprB.

However, when enabling only coprA and installing some packages from this 
copr, we can miss some packages from coprB, because those packages are 
not available since coprB is not enabled.

Solution:
We should be able to define dependency between coprs correctly. When 
creating coprA, we would add one or more depended coprs ('userB/coprB') 
instead of repo link. Then all packages from these coprs would be 
available during build, correct buildroots would be used (no need to 
specify variables $releasever and in addition, we would be able to 
provide correct (all) RPMs also when *installing* coprs.

There are basically two ways how to implement this on the users' side:
1) Simpler, preferred by Mirek, copr maintainer (CC'd):
'copr' plugin in dnf would include -r option, which would basically 
installed all related coprs. That means when running `dnf copr enable -r 
userA/coprA`, user would end with two coprs enabled: userA/coprA and 
userB/coprB.

2) More complicated, preferred by me :) :
copr A repository from example above would not only include RPMs build 
as part of this copr, but would include also packages from copr B. That 
means that when running `dnf copr enable userA/coprA`, user would not 
need to install userB/coprB repository and would have all packages 
available.

Both ways struggle with refreshing data:
* in 1) we might need to refresh coprs enabled (on the users' side)
* in 2) we would need to re-create repodata in depended coprA if coprB 
gets changed (on the server's side).

Let's discuss this a bit, I'm eager to hear your opinions.

Cheers,
Honza