Hints on fixing #2645: Properly merge preferences (dependency resolution)

[Martin Vlk]

Hi folks,
I am a beginner cabal hacker and I have been picking issues to fix,
labeled with "easy".

My next one is https://github.com/haskell/cabal/issues/2645.

I've been trying to read and feel my way through the code and find where
this issue is rooted, but so far I haven't succeeded.

To save me unnecessary effort, could somebody point me at the right
modules/functions where soft constraints/preferences are handled and
also where the corresponding merging functionality is implemented for
hard constraints.

I'll then take it from there, read the code and fix the issue,
potentially asking more questions here.

Many Thanks
Martin