punktfunk/packaging/nix/module-check.nix

# Does the NixOS module actually evaluate, and does it still render the units we decided on?
#
# WHY THIS FILE EXISTS. `nix flake check` does NOT check `nixosModules`. It forces the value and
# asserts it is a lambda taking an open attribute set — nothing more; nix's own source carries
# `// FIXME: if we have a 'nixpkgs' input, use it to check the module.` MEASURED: a flake whose
# `nixosModules.default` sets a nonexistent OPTION, references a nonexistent `pkgs` attribute AND
# calls a nonexistent `lib` function passes clean, printing the thoroughly reassuring
#
#     checking NixOS module 'nixosModules.default'... all checks passed!
#
# So every option name, type, `pkgs.*` reference and systemd directive in nixos-module.nix was
# unverified by CI while reading as covered — on a flake whose own history is Nix regressions
# reaching main invisibly (`nix build .#punktfunk-web` was broken for 553 commits).
#
# HOW IT CLOSES THAT. Exposed as a flake `checks` output, so `nix flake check --no-build` — the leg
# CI already runs — must INSTANTIATE it, and instantiating forces the `assert` below. Every
# assertion is therefore pure Nix, evaluated at instantiation: a shell script inside the derivation
# would only run under a full `nix flake check`, which builds the hour-long Rust packages and is
# exactly what CI cannot afford. Keep it that way — if you add a check, add it to `results`, not to
# a `runCommand` body.
#
# STUB PACKAGES, on purpose. The real derivations would drag punktfunk-host, punktfunk-client and
# (via `gamescopeHdr`) a from-source gamescope into this check's closure, making the cheap leg
# expensive and coupling a module regression to a Rust build. What is under test here is the MODULE.
# ⚠ The stubs must be fake DERIVATIONS, not store-path strings: `types.package` accepts anything
# `isDerivation` as-is, but runs a store-path string through `builtins.storePath`, which demands the
# path actually exist and fails eval with "no substituter can build it".
{
  lib,
  runCommand,
  # The nixpkgs SOURCE. Interpolated rather than `nixpkgs + "/..."` because this is called with the
  # flake INPUT, which is an attribute set (coerced through its `outPath`) and not a path — the
  # difference only shows up as "expected a set but found a string" from whichever side is wrong.
  nixpkgs,
  system,
  module,
}:
let
  fakeDrv = name: {
    type = "derivation";
    inherit name;
    outPath = "/pf-stub/${name}";
    outputs = [ "out" ];
  };

  stubSelf = {
    packages.${system} = lib.genAttrs [
      "punktfunk-host"
      "punktfunk-client"
      "punktfunk-web"
      "punktfunk-scripting"
      "punktfunk-gamescope"
    ] fakeDrv;
  };

  # A machine just complete enough for eval-config, plus the scenario under test.
  evalWith =
    scenario:
    (import "${nixpkgs}/nixos/lib/eval-config.nix" {
      inherit system;
      modules = [
        (module stubSelf)
        {
          boot.loader.grub.enable = false;
          fileSystems."/" = {
            device = "/dev/sda1";
            fsType = "ext4";
          };
          system.stateVersion = "24.11";
          nixpkgs.hostPlatform = system;
          # `host.users` adds group membership to an existing user; declare one so NixOS's own
          # "isNormalUser or isSystemUser" assertion is not what this check trips over.
          users.users.alice.isNormalUser = true;
        }
        scenario
      ];
    }).config;

  # Every scenario keeps `gamescopeHdr = false`: it is the one option whose default would pull a
  # real (stub, here) gamescope onto the unit PATH, and nothing below is about that.
  desktop = evalWith {
    services.punktfunk.host = {
      enable = true;
      users = [ "alice" ];
      gamescopeHdr = false;
      desktopSession = true;
    };
  };

  appliance = evalWith {
    services.punktfunk.host = {
      enable = true;
      autoStart = true;
      openFirewall = true;
      gamescopeHdr = false;
    };
  };

  nativeOnly = evalWith {
    services.punktfunk.host = {
      enable = true;
      openFirewall = true;
      gamestream = false;
      gamescopeHdr = false;
    };
  };

  clientOnly = evalWith { services.punktfunk.client.enable = true; };

  unit = cfg: name: cfg.systemd.user.units."${name}.service".text;
  has =
    cfg: name: infix:
    lib.hasInfix infix (unit cfg name);
  # A module's own failed assertions, as messages.
  failedAssertions = cfg: map (a: a.message) (lib.filter (a: !a.assertion) cfg.assertions);

  results = [
    # --- the module evaluates at all, in every shape an operator can ask for -------------------
    {
      name = "desktop scenario has no failing assertions";
      ok = failedAssertions desktop == [ ];
    }
    {
      name = "appliance scenario has no failing assertions";
      ok = failedAssertions appliance == [ ];
    }
    {
      name = "client-only scenario has no failing assertions";
      ok = failedAssertions clientOnly == [ ];
    }

    # --- the KWin identification trap (packaging/arch/punktfunk-host.install) -------------------
    # The host MUST exec the plain store path. A capability wrapper here would put CAP_SYS_NICE in
    # the process's permitted set, and the kernel then refuses KWin the /proc/<pid>/exe readlink it
    # identifies the client by — which cost every KDE box its desktop streaming in 0.26.0-1.
    {
      name = "host ExecStart is the store binary, never a capability wrapper";
      ok =
        has desktop "punktfunk-host" "ExecStart=/pf-stub/punktfunk-host/bin/punktfunk-host serve"
        && !(has desktop "punktfunk-host" "ExecStart=/run/wrappers");
    }
    # ...while the ENCODE WORKER, which nothing ever has to identify, is pointed at the wrapper.
    {
      name = "host points PUNKTFUNK_ENCODE_WORKER at the capability wrapper";
      ok =
        has desktop "punktfunk-host"
          "PUNKTFUNK_ENCODE_WORKER=/run/wrappers/bin/punktfunk-encode-worker";
    }
    {
      name = "the encode-worker wrapper carries exactly cap_sys_nice=ep";
      ok = desktop.security.wrappers.punktfunk-encode-worker.capabilities == "cap_sys_nice=ep";
    }

    # --- the desktop-login route (scripts/punktfunk-host-desktop-session.conf) -----------------
    # Asserted on the evaluated LISTS, not the rendered text: systemd renders `After=` as one
    # space-separated line, so `hasInfix "After=graphical-session.target"` silently depends on
    # ordering — it failed against a correct module the first time this check ran.
    {
      name = "desktopSession binds the host to graphical-session.target";
      ok =
        let
          u = desktop.systemd.user.services.punktfunk-host;
        in
        lib.elem "graphical-session.target" u.after
        && lib.elem "graphical-session.target" u.partOf
        # IN ADDITION to default.target, never instead of it.
        && lib.elem "graphical-session.target" u.wantedBy;
    }
    {
      name = "desktopSession is NOT applied to the appliance route (it would stay stopped there)";
      ok =
        let
          u = appliance.systemd.user.services.punktfunk-host;
        in
        !(lib.elem "graphical-session.target" u.partOf) && lib.elem "default.target" u.wantedBy;
    }

    # --- GameStream opt-out reaches both the argv and the firewall -----------------------------
    {
      name = "gamestream=true passes --gamestream";
      ok = has desktop "punktfunk-host" "serve --gamestream";
    }
    {
      name = "gamestream=false drops --gamestream and its firewall ports";
      ok =
        !(has nativeOnly "punktfunk-host" "--gamestream")
        && !(lib.elem 47984 nativeOnly.networking.firewall.allowedTCPPorts)
        && lib.elem 47990 nativeOnly.networking.firewall.allowedTCPPorts;
    }
    {
      name = "openFirewall opens the console AND its plugin origin";
      ok =
        lib.elem 47992 appliance.networking.firewall.allowedTCPPorts
        && lib.elem 47993 appliance.networking.firewall.allowedTCPPorts;
    }

    # --- the three divergences from the shipped units, as regression guards --------------------
    # Each of these was ONCE wrong here while right in scripts/*.service. Assert the decision, so a
    # future edit cannot quietly drift back.
    {
      # Without this, systemd's default 5-starts-per-10s against RestartSec=2 gives up permanently
      # after ~10 s — the exact window before the host's first `serve` writes the mgmt token.
      name = "web console retries indefinitely while the host writes its mgmt token";
      ok = has appliance "punktfunk-web" "StartLimitIntervalSec=0";
    }
    {
      # A console that exits 0 has still stopped serving.
      name = "web console restarts on ANY exit, not just failure";
      ok =
        has appliance "punktfunk-web" "Restart=always"
        && !(has appliance "punktfunk-web" "Restart=on-failure");
    }
    {
      # The one unit here that runs arbitrary operator TypeScript by design.
      name = "the plugin runner is sandboxed like the deb/rpm unit";
      ok =
        has appliance "punktfunk-scripting" "NoNewPrivileges=true"
        && has appliance "punktfunk-scripting" "ProtectSystem=strict"
        && has appliance "punktfunk-scripting" "ReadWritePaths=%h"
        && has appliance "punktfunk-scripting" "ReadWritePaths=/tmp"
        && has appliance "punktfunk-scripting" "RestrictAddressFamilies=AF_UNIX";
    }
    {
      # PrivateTmp is OFF on purpose (the VirtualHere field report: a private /tmp hides
      # /tmp/vhclient and /tmp/.X11-unix, so a plugin cannot reach the daemon it integrates with).
      name = "the plugin runner keeps the real /tmp";
      ok = has appliance "punktfunk-scripting" "PrivateTmp=false";
    }
    {
      # Since the library scanners became plugins, a runner that is off means an EMPTY LIBRARY and
      # no obvious reason why — which is why deb+rpm `systemctl --global enable` it.
      name = "the plugin runner is started by default, like every other channel";
      ok = has appliance "punktfunk-scripting" "WantedBy=default.target";
    }

    # --- the client half must not drag the host's system wiring in -----------------------------
    {
      name = "a client-only machine defines no host/web/scripting units";
      ok =
        !(clientOnly.systemd.user.services ? punktfunk-host)
        && !(clientOnly.systemd.user.services ? punktfunk-web)
        && !(clientOnly.systemd.user.services ? punktfunk-scripting);
    }
  ];

  failures = map (r: r.name) (lib.filter (r: !r.ok) results);
in
# The `assert` is what makes `--no-build` sufficient: instantiating this derivation forces it.
assert
  failures == [ ]
  || throw ''
    The punktfunk NixOS module no longer renders what packaging/nix/module-check.nix requires.
    Failing checks (${toString (lib.length failures)} of ${toString (lib.length results)}):
      - ${lib.concatStringsSep "\n    - " failures}
  '';
runCommand "punktfunk-nixos-module-check"
  {
    # Recorded in the output so a green run says what it actually covered.
    passed = toString (lib.length results);
  }
  ''
    echo "punktfunk NixOS module: $passed checks passed at eval time" > "$out"
  ''