hyperhive/nix/module-eval.nix

# `checks.module-eval` — the flake check that covers **nix**.
#
# Why this exists: every other check in ./checks.nix is a Rust
# derivation, so a `.nix`-only diff moves no hash, every check is a
# cache hit, and `nix flake check` reports green **without evaluating
# what changed**. This one's derivation hash is a function of the
# evaluated *results* below, so a nix change that flips a property
# rebuilds it and the builder fails naming that property.
#
# ## What belongs here, and what does not
#
# Anything expressible as a module `assertion` **should be one instead**:
# an assertion fires at deploy time for a real operator, not only in CI.
# What cannot be an assertion is the **absence class** — "a hive that
# hasn't opted in renders exactly what it did before", "this unit does
# not exist unless X". Those are claims about the *rendered config*
# rather than about a config being invalid, so they need an evaluator.
#
# ⚠️ **Cases are named by the PROPERTY they defend, never by the ticket
# that prompted them.** A case named after a ticket has the ticket's
# lifetime; a case named after a property lives as long as the property.
#
# ⚠️ **This check evaluates. It does not execute.** Where the artifact is
# a command line, an HTTP request or a certificate, a value assertion
# cannot stand in — those need something that *runs* them. And a case
# that needs a **rendered file** must stub the packages that file drags
# in (`swarm.ui.package = pkgs.emptyDirectory`), or it costs a full
# frontend build to answer a question about a listen directive.
{
  pkgs,
  lib,
  self,
  nixosSystem,
}:
let
  # Stub host, same shape ./docs/default.nix already uses: enough for a
  # `nixosSystem` to evaluate, nothing that pulls a real disk or
  # bootloader in.
  hive =
    extra:
    (nixosSystem {
      system = pkgs.stdenv.hostPlatform.system;
      modules = [
        self.nixosModules.default
        {
          fileSystems."/" = {
            device = "/dev/null";
            fsType = "tmpfs";
          };
          boot.loader.grub.enable = false;
          system.stateVersion = "25.11";
          # `recursiveUpdate`, not `//`: a plain `//` only merges the
          # *top-level* keys of `extra` in, so an `extra` that touches a
          # nested attr under an existing top-level key (e.g. `swarm.*`)
          # silently drops every sibling under that key instead of merging
          # into it — the same class of bug as the `services.hyperhive`
          # double-nesting mistake this stub already had to dodge once,
          # just one level down. `recursiveUpdate` merges nested attrsets
          # all the way down instead.
          services.hyperhive = lib.recursiveUpdate {
            enable = true;
            hiveName = "h1";
            swarm.domain = "t.local";
            swarm.hives.h1.domain = "h1.t.local";
          } extra;
        }
      ];
    }).config;

  allLocal = hive { enableAllLocalDefaults = true; };
  bare = hive { };
  withCi = hive { deploy.forgejo.ci.enable = true; };

  # A priority collision is a property of the *option*, not
  # of the merged value's interior — nix throws the moment the value is
  # demanded at all, so `seq`-ing each `serviceConfig` value to WHNF is
  # both necessary and sufficient. `deepSeq` over-specifies this: it keeps
  # walking *into* the resulting value after the merge already succeeded,
  # and a package/derivation-shaped value's `override`/`overrideAttrs`
  # self-reference sends it into nixpkgs' fixpoint machinery and blows the
  # stack (measured — this is not a hypothetical).
  forceCiServiceConfigs =
    let
      svcs = withCi.containers.hive-ci.config.systemd.services;
      vals = lib.concatMap (s: builtins.attrValues (s.serviceConfig or { })) (builtins.attrValues svcs);
    in
    builtins.foldl' (acc: v: builtins.seq v acc) true vals;

  # Each case: a name stating the property, and `ok`.
  cases = [
    {
      name = "a hive that has not opted into all-local runs no swarm controller";
      ok = !bare.services.hyperhive.deploy.swarm-controller.enable;
    }
    {
      name = "the all-local mode turns the swarm controller on";
      ok = allLocal.services.hyperhive.deploy.swarm-controller.enable;
    }
    {
      # The gateway's per-name issuer choice. If this ever collapses to a
      # constant, every swarm-service vhost serves a certificate its CA
      # is name-constrained out of — which evaluates cleanly and fails in
      # a browser.
      name = "a swarm service name gets the swarm-services leaf and the default server does not";
      ok =
        let
          l = allLocal.services.hyperhive.gateway.lib;
        in
        (l.tlsFor "t.local").sslCertificate != (l.tlsFor "_").sslCertificate;
    }
    {
      # nixos asserts when a vhost declares both, so this is also a
      # statement that the `removeAttrs` upstream of it still happens.
      name = "the swarm UI vhost forces TLS instead of merely adding it";
      ok =
        let
          v = allLocal.services.nginx.virtualHosts."t.local";
        in
        v.forceSSL && !(v.addSSL or false);
    }
    {
      name = "a hive with matrix off serves no matrix discovery endpoint";
      ok =
        !(builtins.hasAttr "= /.well-known/matrix/client" bare.services.nginx.virtualHosts."_".locations);
    }
    {
      # main got eval-borked twice by this exact class of bug (once on the
      # unit's `Restart` key, once on `RestartSec`) — a nixpkgs bump to
      # `gitea-actions-runner.nix` adds a plain `serviceConfig.*`
      # definition that collides with one of ours, and nix refuses to
      # merge two plain definitions at *host* eval. No other check
      # instantiates a host with `containers.hive-ci` actually enabled, so
      # the collision only surfaces on operator deploy, not in CI.
      name = "the CI container's unit definitions merge without a priority collision";
      ok = forceCiServiceConfigs;
    }
  ];

  bad = builtins.filter (c: !c.ok) cases;
  report = lib.concatMapStringsSep "\n" (c: "  echo 'FAILED: ${c.name}' >&2") bad;
in
# The results are embedded in the builder text on purpose: that is what
# makes this derivation's hash depend on them, so a nix-only change that
# flips a case cannot be answered from cache.
pkgs.runCommand "hyperhive-module-eval" { } ''
  ${report}
  ${
    if bad == [ ] then
      "echo '${toString (builtins.length cases)} module properties hold' && touch $out"
    else
      "echo 'module-eval: ${toString (builtins.length bad)} of ${toString (builtins.length cases)} properties broke' >&2 && exit 1"
  }
''