[clhodapp]

Adds caisson.hjem, an integration over hjem whose configurations are the files and packages of one user.

What an hjem configuration is

hjem evaluates a user only inside its NixOS and nix-darwin modules, as an entry of hjem.users. caisson evaluates hjem's user module, modules/common/user.nix, with its own evalModules. It passes the arguments hjem's OS modules pass: hjem's library as hjem-lib, the user's name as name, the package set as pkgs, and the machine above the configuration as osConfig. user defaults to the name the configuration is declared under. The configuration is found by that name in configs/hjem.

The outputs are what hjem's tools read:

Output	Value
manifest	the version 3 manifest of the user's files, as hjem's OS modules write it
manifestFile	that manifest as a JSON file, checked against hjem's schema with cue vet when built
packages	the user's packages
cli	hjem's CLI, built from the hjem source the configuration is evaluated with

A top publishes the configuration as hjemConfigurations.<name> with manifest and packages. That is the attribute hjem standalone switch --flake . reads for $USER. The value of an hjem configuration that is a top has manifest and packages as well, which hjem standalone switch --config reads from a file. The manifest of the evaluation sits under caisson.manifest behind an outPath, so the CLI serializes it as a string.

Inside a NixOS machine

caisson does not use hjem's NixOS module. The new NixOS module hjem-activation, imported by caisson's default NixOS module, writes the units hjem's NixOS module writes, under the same names. These are hjem-prepare, the templates hjem-activate@, hjem-reload@ and hjem-update-state@, hjem-cleanup and the target hjem. The unit scripts are the same, with strict shell checks, and they read the manifests of the generation from one directory. Each instance runs the CLI of the configuration of its user. The module also adds each user's packages to users.users.<user>.packages and the user's extraDependencies to the system closure, as upstream does.

Through caisson.forChildren, caisson's default NixOS module gives each hjem configuration the hjem module nixos-parent. That module sets directory from the machine's account for the user, and refuses a user without an enabled account. An hjem configuration inside a NixOS machine also imports hjem's modules/nixos/systemd.nix with the machine's utils and options. As a result, it can declare systemd user units, like a user embedded by hjem's NixOS module.

The units link with hjem's own CLI and the backup prefix .backup-. hjem's NixOS options for another linker or for systemd-tmpfiles have no counterpart.

The cost of one more integration

Every evaluation declares a caisson.<integration>.configurations option for every integration, and childrenOf read all of them. The first commit makes childrenOf read only the options that a module defines, and builds the option types once. With hjem added, caisson's evaluation overhead in the eval-weight check drops from 4.26 MB to 4.15 MB, and the ceiling stays 4.28 MB.

Tests

• The pinned-world suite pins hjem in tests/dependencies and checks two cases.
  • A standalone top gives the manifest, packages and placeholder the CLI reads.
  • An hjem configuration inside a NixOS machine takes its directory from the account. Its manifest, which includes a systemd user unit, equals the manifest hjem's NixOS module makes from the same user module. The machine has the template units and requires the instance for the user, and the top publishes hjemConfigurations.probe.
• The new hjem-system check builds the manifest file, which runs cue vet against hjem's schema, and the six units, which runs shellcheck on their scripts.
• The unit tests and the argument-errors check cover the new entry points.

Activation on a running machine is not tested.

All 18 workspace consumers pass nix flake check --no-build at #96, which contains this branch. That run puts the branch in place of both caisson pins of each consumer: the root input, and the tests/dependencies lock that the checks partition reads. An earlier run on this branch alone overrode only the root input, so those partitions then ran against the caisson they pin.

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