A build graph can now dynamically change during builds by rolling dice

The introduction of dynamic derivations represents a significant change in how the build graph operates within Nix. Instead of requiring a complete understanding of the build graph prior to execution, builds can now be defined and modified on the fly. This means that the next steps in a build can depend on outcomes from prior steps, allowing for more dynamic and flexible workflows.

The cost of adopting this new approach may involve a learning curve for developers accustomed to the traditional applicative model. They will need to understand how to structure builds to take advantage of this flexibility and how to handle potential complexities that arise from dynamically changing build graphs.

However, the change does not come without limitations. While dynamic derivations provide powerful new capabilities, they also introduce potential pitfalls. Developers must be cautious about how dependencies are managed, as the increased complexity can lead to longer build times or difficulty in debugging.

The shift from an applicative to a monadic build system has implications for performance as well. The ability to run builders in parallel and leverage remote machines for execution can significantly enhance build efficiency. This could lead to reduced overall build times, especially in large projects with complex dependencies.

In summary, the move towards dynamic derivations in Nix is a substantial evolution that allows for greater flexibility and efficiency in build processes. It encourages developers to rethink how they conceptualize and implement builds, opening up new possibilities for automation and optimization.