podman: add darwin support with machine management

[delafthi]

• restructure module from podman-linux to platform-agnostic podman
• move linux-specific implementation to modules/services/podman/linux/
• add darwin module with declarative machine management
• implement launchd-based watchdog for auto-starting machines
• maintains backward compatibility with existing linux functionality

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[n-hass]

I've just had a skim and will take a more thorough look later. Thanks for the contribution.

I don't believe it's conventional to namespace service settings under the platform the feature is available for, eg the services.podman.darwin.machines. Instead give the user a useful error if they configure a machine on a non-Darwin system.

Any thoughts anyone else?

[khaneliman]

I agree I don't really like darwin namespacing really... Should be able to hide options / disable options on darwin if they can't be used.

          visible = pkgs.stdenv.hostPlatform.isLinux;
          readOnly = pkgs.stdenv.hostPlatform.isDarwin;

or just don't make them available through not importing ?

[delafthi]

Any thoughts anyone else?

I agree. An implementation without a darwin namespace would be nicer.

[delafthi]

@n-hass just a ping. I removed the darwin namespace.

[n-hass]

Can you make these imports conditional on platform? That way respective platforms will not have visibility of the invalid options. eg

  imports =
    lib.optional pkgs.stdenv.hostPlatform.isLinux ./linux/default.nix
    ++ lib.optional pkgs.stdenv.hostPlatform.isDarwin ./darwin.nix;

[delafthi]

I tried this, but I think conditional imports are not allowed - at least not this way. I get the following error, when running the tests with conditional imports:

> make test TEST=podman-configuration
nix-shell --pure tests -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz -A run.podman-configuration
unpacking 'https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz' into the Git cache...
error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'nmt-run-podman-configuration'
         whose name attribute is located at /nix/store/8pskd9fpj2lgv6fjyyvhhxvw4bmayfnd-source/pkgs/stdenv/generic/make-derivation.nix:541:13

       … while evaluating attribute 'shellHook' of derivation 'nmt-run-podman-configuration'
         at /nix/store/fm1dwqb08lxr1gk02niyvb1j7v4181c0-source/default.nix:38:41:
           37|   runShellOnlyCommand = name: shellHook:
           38|     pkgs.runCommandLocal name { inherit shellHook; } ''
             |                                         ^
           39|       echo This derivation is only useful when run through nix-shell.

       … while evaluating the module argument `pkgs' in "/home/deaa/Developer/personal/home-manager/modules/services/podman":

       … noting that argument `pkgs` is not externally provided, so querying `_module.args` instead, requiring `config`

       … if you get an infinite recursion here, you probably reference `config` in `imports`. If you are trying to achieve a conditional import behavior dependent on `config`, consider importing unconditionally, and using `mkEnableOption` and `mkIf` to control its effect.

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: infinite recursion encountered
make: *** [Makefile:14: test] Error 1

@khaneliman do you know of a way to resolve this problem?

[n-hass]

Impl looks good - just one small thing about guarding imports by platform.