So far, the environment used by `command` was completely leaky and the
one used by `nix` was very leaky despite it trying to be a "hermetic"
environment.
This commit moves the hermaticity to `command` and changes its
implementation to be not leak anything.
To achieve this, the following changes were also nessecary:
- the `files` and `snapshot` fixture now use the folder `test-home`
within the tmp_path directory by default, as the `HOME` environment
variable is set to there. (extraction not possible due to dependencies
of command etc also using this directory)
Fixes: #847, #848
Change-Id: I55f86ee0e1615e73fcf442ee2f28f3b89893bbb4
Most of these are simple fixes and clarifications. One set of fixes will
come in the commit that actually upgrades nixpkgs and hence ruff as it
will otherwise cause errors here.
Change-Id: Ie857da0f6cf728478700ec2d24cf518f8c7b7815
This also rewrites a lot of the command handling in the fixtures
library, since we want to more precisely control which way that the nix
store is set up in the tests, rather than the previous method of
renaming /nix/store to some temp dir (which allows builds but does not
allow any /nix/store paths or stability across runs, which is a
significant issue for snapshot testing).
It uses a builder to reduce the amount of state carelessly thrown
around.
The evil NARs are inspired by CVE-2024-45593
(https://github.com/NixOS/nix/security/advisories/GHSA-h4vv-h3jq-v493).
No bugs were found in this endeavor.
Change-Id: Iee41b055fa96529c5a3c761f680ed1d0667ba5da
