link to search.nixos.org instead of pulling package metadata out of pkgs. this
lets us cache docs of a few more modules and provides easier access to package
info from the HTML manual, but makes the manpage slightly less useful since
package description are no longer rendered.
most modules can be evaluated for their documentation in a very
restricted environment that doesn't include all of nixpkgs. this
evaluation can then be cached and reused for subsequent builds, merging
only documentation that has changed into the cached set. since nixos
ships with a large number of modules of which only a few are used in any
given config this can save evaluation a huge percentage of nixos
options available in any given config.
in tests of this caching, despite having to copy most of nixos/, saves
about 80% of the time needed to build the system manual, or about two
second on the machine used for testing. build time for a full system
config shrank from 9.4s to 7.4s, while turning documentation off
entirely shortened the build to 7.1s.
by default a ps/2 keyboard input is used which seems to cause issues
on aarch64-linux when the machine is used high load, causing the keymap
qwertz test to always fail and azerty to sometimes fail
See https://github.com/NixOS/nixpkgs/issues/147294
some options have default that are best described in prose, such as
defaults that depend on the system stateVersion, defaults that are
derivations specific to the surrounding context, or those where the
expression is much longer and harder to understand than a simple text
snippet.
the default hasn't been changed since 2009
this can improve our test performances
nixos/tests: remove explicit memorySize <1024
1024MiB is now the default
Since e791519f0f ("nixos/qemu-vm: use qemu_kvm"), VMs generated with
nixos-rebuild build-vm use the qemu_kvm package instead of the qemu
package. (The difference between them is that qemu_kvm is only built
with support for the host architecture, not all architectures.)
But with this change, nixos-rebuild build-vm would now depend on
_both_ QEMUs, because the guest agent module was still using the one
from the full QEMU package. There's no need for it to use this
instead of the lighter qemu_kvm, because the guest agent shouldn't be
affected by which platforms QEMU can emulate.
The default has been unchanged for a decade. Space is cheaper and
software catches up with that. Let's not make our testing harder
than necessary by default.
