In preparation for bumping the LLVM used by Darwin, this change
refactors and reworks the stdenv build process. When it made sense,
existing behaviors were kept to avoid causing any unwanted breakage.
However, there are some differences. The reasoning and differences are
discussed below.
- Improved cycle times - Working on the Darwin stdenv was a tedious
process because `allowedRequisites` determined what was allowed
between stages. If you made a mistake, you might have to wait a
considerable amount of time for the build to fail. Using assertions
makes many errors fail at evaluation time and makes moving things
around safer and easier to do.
- Decoupling from bootstrap tools - The stdenv build process builds as
much as it can in the early stages to remove the requirement that the
bootstrap tools need bumped in order to bump the stdenv itself. This
should lower the barrier to updates and make it easier to bump in the
future. It also allows changes to be made without requiring additional
tools be added to the bootstrap tools.
- Patterned after the Linux stdenv - I tried to follow the patterns
established in the Linux stdenv with adaptations made to Darwin’s
needs. My hope is this makes the Darwin stdenv more approable for
non-Darwin developers who made need to interact with it. It also
allowed some of the hacks to be removed.
- Documentation - Comments were added explaining what was happening and
why things were being done. This is particular important for some
stages that might not be obvious (such as the sysctl stage).
- Cleanup - Converting the intermediate `allowedRequisites` to
assertions revealed that many packages were being referenced that no
longer exist or have been renamed. Removing them reduces clutter and
should help make the stdenv bootstrap process be more understandable.
