[grumbel]

When you build into the store, you have to rebuild from scratch. However Nix does allow incremental builds inside your source directory as well. If you spawn a development shell like:

    nix develop .

All the build phases are available as shell functions or variables (unpackPhase, patchPhase, configurePhase, buildPhase, ...). The phases depend on each other, so if you want to skip a phase some additional tweaking or setting of environment variables will be necessary. The "genericBuild" function is the top level entry point for a normal build, the source can be viewed via:

   declare -f genericBuild

and should give a bit of an idea what Nix is doing.