Format all Nix files using the officially approved formatter,
making the CI check introduced in the previous commit succeed:
nix-build ci -A fmt.check
This is the next step of the of the [implementation](https://github.com/NixOS/nixfmt/issues/153)
of the accepted [RFC 166](https://github.com/NixOS/rfcs/pull/166).
This commit will lead to merge conflicts for a number of PRs,
up to an estimated ~1100 (~33%) among the PRs with activity in the past 2
months, but that should be lower than what it would be without the previous
[partial treewide format](https://github.com/NixOS/nixpkgs/pull/322537).
Merge conflicts caused by this commit can now automatically be resolved while rebasing using the
[auto-rebase script](8616af08d9/maintainers/scripts/auto-rebase).
If you run into any problems regarding any of this, please reach out to the
[formatting team](https://nixos.org/community/teams/formatting/) by
pinging @NixOS/nix-formatting.
The seekable format splits compressed data into a series of independent
frames, each of which can be decompressed individually. This allows to
distribute images in smaller chunks and allows image downloads to be
paused and resumed later from the same point.
Seekable archives as a whole can be decompressed with any regular zstd
decompressor. However, partial decompression requires to know the
starting position of the desired frame, which can be extracted from a
skippable frame (aka seektable) that is appended to the compressed data.
Having access to the original Nix partition definitions in the builder
should make it a bit easier to manipulate them and still provide access
to the manipulated results.
As a follow-up to https://github.com/NixOS/nixpkgs/pull/294096 this
should further improve the flexibility around building OS images with
systemd-repart:
* Previously the attribute set `compression` needed to be fully
populated, including `algorithm` and `level` because
`compression.enable` was evaluated by bash, after being interpolated
as strings into the `buildCommand`. Now it's sufficient to pass
`compression.enable = false` to the builder, e.g. in `overrideAttrs`,
to disable the compression.
* Using mkDerivation allows for much more customization than the
previously used `runCommand`, making use of phases and pre/post hooks.
This is especially helpful for building multiple images from the same
system configuration, e.g. to build an image `Y` based on a partially
built raw image `X`, by injecting a UKI that depends on `X` into a
defered ESP.
* Before this change it was non-trivial to conduct further manipulations
on the amended repart definitions. Now, the definitions that
systemd-repart uses to build the image can be easily manipulated in
`postPatch` or `preBuild`.
Aside from this, the build is now executed in the build directory, rather
than `$out`. This allows references to relative paths in the build
environment to be used, especially for `--definitions`, which previously
required an absolute path.
Parameters passed to systemd-repart are now passed to the build script
via environment variable, which is defined as a list of strings in
combination with `__structuredAttrs = true`. This should make it easier
to customize the image build using `overrideAttrs`.
Both the script used to amend the repart definitions and the amended
definitions are now available via passthru.
The version option is needed if you want to implement partition &
systemd-boot based A/B booting where the version information is encoded
in the files on the ESP. See systemd-sysupate docs for more details on
this:
https://www.freedesktop.org/software/systemd/man/latest/sysupdate.d.html
Note, however, that this is not *only* useful for systemd-sysupdate but
also for other similar updating tools/mechanisms.
Since the repart image is built on the build platform, use
`buildPackages` to construct the image. This allows for systemd-repart
images for cross-compiled nixos configurations to work properly.
