DNF: "There are following alternatives to this package"

[Tomas Orsava]

Hi!
We'd like to propose a new functionality for dnf: When a user tries to 
install a package XYZ and dnf doesn't find it, dnf would recommend them 
alternative packages. These offered packages would advertise that they 
are an alternative for XYZ using a specially formatted Provides tag.

For example, packages `python2-requests` and `python3-requests` would 
both have the following tag:

     Provides: alternative-for(python-requests) = %{version}-%{release}

(Possibly via the already existing and widespread %python_provide macro 
in the Python case.)

And when the user would try to install `python-requests`, dnf would look 
for packages with the relevant Provides tag and display them:

     # dnf install python-requests
       * There are following alternatives to this package: 
python2-requests python3-requests
     No match for argument: python-requests
     Error: Unable to find a match

This would be very similar to an already existing functionality that 
searches for lowercase package names:

     # dnf install python3-REQUESTS
       * Maybe you meant: python3-requests
     No match for argument: python3-REQUESTS
     Error: Unable to find a match

(That functionality is broken in some versions—RHBZ#1628514—so you might 
not see this result at the moment.)

What are your thoughts?

One possible addition would be to include a parameter for weight in the 
Provides tag, so that python3-requests could be listed as the preferred 
option before python2-requests.

All the best,
Tomas Orsava