Wolf will welcome everyone and say a couple of words about PackagingCon and how we are going and how the virutal conference is going to work

Keynote

Todd Gamblin, Steven! Ragnarök and Matthias Meschede are going to talk about "The Taxonomy of Package Managers" – expect a fun talk about the history of package management and an overview of the different species of package managers out there

Most package managers need a dependency solver, but dependency solving is an NP-hard problem, and writing a correct solver from scratch is difficult to do correctly, let alone a fast solver. Simply understanding the solution space is a challenge, from simple SAT solvers, to specialized solutions like PubGrub and libsolv, to Satisfiabilty Modulo Theories (SMT) and Answer Set Programming (ASP) solvers. Solvers may need to optimize for multiple objectives -- preferring the most recent versions of dependencies is common, but multi-valued build options, optional dependencies, virtual dependencies, and build options like compilers, architectures, and ABI compatibility can also factor into a solve.

We have recently shipped a new solver in the Spack package manager that relies on the clingo Answer Set Programming (ASP) framework to accomplish many of these goals. We'll talk about how we handle complex features like optional dependencies, generalized conditions, virtual dependencies (interfaces), compiler selection, ABI options, and multiple optimization criteria in around 500 lines of declarative code. We'll talk about some of the semantics of ASP that lend themselves to very general package solving (vs other models like SMT). Finally, we'll show some performance numbers with large package repositories.

We’ve managed to bring all of you together from different package manager communities, but can we also bring the package managers you work on together? Is there room for one package manager to rule them all, or will package management always be a very domain-centric activity? If it does, is that good or bad?