cinereal 608690995f nixos/modular-services: add portable process.environment
Adds modular service option `process.environment` to pass an attrset of
env vars to the service manager.
`null` values actively unset the variable before the process starts.

Values are `coercedTo (either path package) str` via interpolation,
mirroring `pathOrStr`, so paths and packages render to store-path strings
with string context preserved. The type is `lazyAttrsOf`, allowing one
entry to reference another (recursive env definitions).

The systemd backend unsets entries using `unexport` in `ExecStart`,
so the variable is absent even when `Environment=` or
the inherited environment would otherwise supply it.

The systemd backend lifts non-null entries onto the primary unit wrapped
per-key with `lib.mkDefault` so they merge with the existing priority-100
`environment.PATH` binding in `nixos/lib/systemd-lib.nix` while still letting
explicit `systemd.service.environment.<k>` overrides win.

The systemd extra-root modules are loaded via `importApply`, closing `pkgs`
over `systemd/service.nix` as a non-module argument (matching the portable
`lib/services/service.nix` convention) instead of passing a redundant `pkgs`
specialArg. The docs eval threads `pkgs = throw` accordingly.

Portable coverage lives in `testers.modularServiceCompliance`: an eval-level
check that a set value round-trips and a `null` value is preserved, plus an
integration test that records the service's own `/proc/$$/environ` and asserts
the set variable is present and the null variable is absent. The
systemd-specific grep assertions in `systemd/test.nix` cover how systemd
achieves this (`Environment=` rendering, null filtering, the `unexport`
wrapper, and override precedence).

Assisted-by: Claude:claude-opus-4-8
2026-07-11 22:54:46 +02:00

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