When a NixOS system uses flakes, i.e., /etc/nixos/flake.nix exists, it
is impossible to use nixos-rebuild to build a pre-flake
configuration.nix. Of course, one can directly use nix command to
build the configuration, but not everybody remembers the correct nix
options to do that.
With the new option, it is possible to build a pre-flake configuration
with command like this:
nixos-rebuild build-vm -I nixos-config=./vm.nix --no-flake
The option might be useful for people following older pre-flake
tutorials on a flake-based system.
--quiet decreases the logging verbosity level (inverse of -v)
--print-build-logs prints build logs on stderr (same as -L)
Also reordered and grouped some options for consistency
When something changes in nixos-rebuild, we must make sure the
installers still work, otherwise it might break existing setups.
The installer tests check whether nixos-rebuild works, so they are a
good lithmus test.
nixos-rebuild would forward all verbose flags to nix, but not actually
increase its own verbosity.
Which would make it hard to see what’s going on without resorting to
tools like strace or adding `set -x` to the script.
We add a simple exec wrapper around the most “interesting” commands,
that is nix tool invocations. If any verbosity flag is given, it will
set the verbosity flag of the nixos-rebuild script all commands
wrapped into `runCmd` will start logging their invocation.
This is done via a `logVerbose` function, which can also be used to
print logging messages when in verbose mode, to aid debugging why
nixos-rebuild does what it does. A few messages are added, but
potentially we could log a lot more details.
Now, testing all of the changed code paths turns out to be rather
hard, so I am unsure how to verify that for all changed commands
behaviour stays indeed the same.
To support this theoretically, the configure script upstream would need
to a) stop using PATH for finding python-config exclusively and allow
passing an absolute path to it and b) cease using the distutils module
for configuration purposes which of course requires running the host
python interpreter which is not possible in the cross case.
Conflict in pkgs/development/libraries/libvirt/default.nix
required manual adjustments. The fetched patch is already in src.
I checked that libvirt builds.
