708074ae6d
Import-from-derivation (IFD) has problematic performance, and is disabled in Nixpkgs by policy. It is arguably good practice for libraries to avoid it whenever possible, as it has poor ergonomics in some cases, especially with dry builds, as it requires multiple eval+build phases. As such, prevent its use in Home Manager by default by putting existing tests that use IFD behind a config. In CI, run a first pass with IFD disabled, skipping tests without the config. Then run a second pass with IFD enabled and including tests with the config. This second pass will also run tests without the config, but they should be cached from the previous run, so the cost is not double (only eval time should be paid twice). It’s necessary to change from using NMT’s `run` to `build` as `run` itself uses IFD. Of the tests that have the config: - kitty/theme-to-themeFile: this is a test for deprecated config, and so should be removed eventually anyway - podman: the implementation relies on IFD to create individual systemd units from the derivation output, and so it is not straightforward to remove the IFD; doing so would require rethinking how the module works to instead have the systemd unit files included as-is rather than as individually configured units in the Nix config.
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Tests
Home Manager includes a basic test suite and it is highly recommended to include at least one test when adding a module. Tests are typically in the form of "golden tests" where, for example, a generated configuration file is compared to a known correct file.
It is relatively easy to create tests by modeling the existing tests,
found in the tests project directory. For a full reference to the
functions available in test scripts, you can look at NMT's
bash-lib.
The full Home Manager test suite can be run by executing
$ nix-build --pure --option allow-import-from-derivation false tests -A build.all
in the project root. List all test cases through
$ nix-build --pure tests --option allow-import-from-derivation false -A list
and run an individual test, for example alacritty-empty-settings,
through
$ nix-build --pure tests --option allow-import-from-derivation false -A build.alacritty-empty-settings
However, those invocations will impurely source the system's Nixpkgs,
and may cause failures. To run against the Nixpkgs from the flake.lock file,
use instead e.g.
$ nix build --reference-lock-file flake.lock --option allow-import-from-derivation false ./tests#test-all
or
$ nix build --reference-lock-file flake.lock --option allow-import-from-derivation false ./tests#test-alacritty-empty-settings
Some tests may be marked with enableLegacyIfd, those may be run by run with e.g.
$ nix-build --pure tests --arg enableLegacyIfd true -A build.mytest