RFC — Towards a new solver for `libmamba` about mamba

[Hind-M]

The general plan seems legit broadly speaking.

• Regarding the Database, we could use a base class as you suggested, or try and isolate the parts specific to libsolv in a specific class to use inside Database (because resolvo's API could be very different) but at least Database is already connected to the rest of mamba and hopefully we won't need to change much.
• Instead of moving everything in mamba::solver::libsolv to mamba::solver, we may want to leave it as it is and try in the same way to isolate what's related to libsolv and what would be common with resolvo.
  Unsolvable for example seems to be tightly linked with libsolv internals so that would be a class specific to libsolv and we should maybe wrap it into another one alongside something else for resolvo (we may need to define its API first to know what to do, I don't know if that work has been done yet).
  So maybe just a renaming would be enough to make it clear it's libsolv specific, or actually keep the same names and just have two namespaces libsolv and resolvo
• Same for repo_info
• parameters seem general enough, but maybe some classes/structs are specific to libsolv (no equivalent in resolvo, semantically speaking)
• Why detemplate Database::add_repo_from_packages? It seems ok to me

[jjerphan]

Regarding the Database, we could use a base class as you suggested, or try and isolate the parts specific to libsolv in a specific class to use inside Database (because resolvo's API could be very different) but at least Database is already connected to the rest of mamba and hopefully we won't need to change much.

I should have mentioned that resolvo's public API exposes a DependencyProvider (similar to a Database) and a Solver. Based on the initial POC, I am quite confident that we could have similar abstractions for resolvo.

Most of the design points are mostly based on the assumption that introducing bases classes is the right pathway and that the current other abstractions than Database and Solver can be decoupled from libsolv, but we need to validate that this is the right approach (I am pretty sure there are other designs which would avoid having a set of base classes and solver-specific sets of concrete classes).

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Edit: For alternatives, I wonder whether template classes with a common template type parameter for the solver could help.