refactor(ops): Split //ops/nixos into different locations

Splits //ops/nixos into:

* //ops/nixos.nix - utility functions for building systems
* //ops/machines - shared machine definitions (read by readTree)
* //ops/modules - shared NixOS modules (skipped by readTree)

This simplifies working with the configuration fixpoint in whitby, and
is overall a bit more in line with how NixOS systems in user folders
currently work.

Change-Id: I1322ec5cc76c0207c099c05d44828a3df0b3ffc1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2931
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: glittershark <grfn@gws.fyi>

ops/machines/all-systems.nix

@@ -1,6 +1,6 @@
 { depot, ... }:
 
-(with depot.ops.nixos; [
+(with depot.ops.machines; [
   whitby
 ]) ++
 

ops/machines/whitby/default.nix

@@ -1,30 +1,31 @@
-{ depot, lib, pkgs, ... }:
+{ depot, lib, pkgs, ... }: # readTree options
+config: # passed by module system
 
 let
   inherit (builtins) listToAttrs;
   inherit (lib) range;
 in lib.fix(self: {
   imports = [
-    "${depot.depotPath}/ops/nixos/clbot.nix"
-    "${depot.depotPath}/ops/nixos/irccat.nix"
-    "${depot.depotPath}/ops/nixos/monorepo-gerrit.nix"
-    "${depot.depotPath}/ops/nixos/panettone.nix"
-    "${depot.depotPath}/ops/nixos/paroxysm.nix"
-    "${depot.depotPath}/ops/nixos/smtprelay.nix"
-    "${depot.depotPath}/ops/nixos/sourcegraph.nix"
-    "${depot.depotPath}/ops/nixos/tvl-buildkite.nix"
-    "${depot.depotPath}/ops/nixos/tvl-slapd/default.nix"
-    "${depot.depotPath}/ops/nixos/tvl-sso/default.nix"
-    "${depot.depotPath}/ops/nixos/www/b.tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/cache.tvl.su.nix"
-    "${depot.depotPath}/ops/nixos/www/cl.tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/code.tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/cs.tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/login.tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/tazj.in.nix"
-    "${depot.depotPath}/ops/nixos/www/todo.tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/tvl.fyi.nix"
-    "${depot.depotPath}/ops/nixos/www/wigglydonke.rs.nix"
+    "${depot.depotPath}/ops/modules/clbot.nix"
+    "${depot.depotPath}/ops/modules/irccat.nix"
+    "${depot.depotPath}/ops/modules/monorepo-gerrit.nix"
+    "${depot.depotPath}/ops/modules/panettone.nix"
+    "${depot.depotPath}/ops/modules/paroxysm.nix"
+    "${depot.depotPath}/ops/modules/smtprelay.nix"
+    "${depot.depotPath}/ops/modules/sourcegraph.nix"
+    "${depot.depotPath}/ops/modules/tvl-buildkite.nix"
+    "${depot.depotPath}/ops/modules/tvl-slapd/default.nix"
+    "${depot.depotPath}/ops/modules/tvl-sso/default.nix"
+    "${depot.depotPath}/ops/modules/www/b.tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/cache.tvl.su.nix"
+    "${depot.depotPath}/ops/modules/www/cl.tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/code.tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/cs.tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/login.tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/tazj.in.nix"
+    "${depot.depotPath}/ops/modules/www/todo.tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/tvl.fyi.nix"
+    "${depot.depotPath}/ops/modules/www/wigglydonke.rs.nix"
     "${pkgs.path}/nixos/modules/services/web-apps/gerrit.nix"
   ];
 

ops/modules/default.nix

@@ -0,0 +1,2 @@
+# Make readTree happy at this level.
+_: {}

ops/nixos.nix

@@ -1,21 +1,8 @@
-# Most of the Nix expressions in this folder are NixOS modules, which
-# are not readTree compatible.
-#
-# Some things (such as system configurations) are, and we import them
-# here manually.
-#
-# TODO(tazjin): Find a more elegant solution for the whole module
-# situation.
+# Helper functions for instantiating depot-compatible NixOS machines.
 { depot, lib, pkgs, ... }@args:
 
 let inherit (lib) findFirst isAttrs;
 in rec {
-  whitby = import ./whitby/default.nix args;
-
-  # System installation
-
-  allSystems = import ./all-systems.nix args;
-
   # This provides our standard set of arguments to all NixOS modules.
   baseModule = { ... }: {
     _module.args = {
@@ -36,7 +23,7 @@ in rec {
     (findFirst
       (system: system.config.networking.hostName == hostname)
       (throw "${hostname} is not a known NixOS host")
-      (map nixosFor allSystems));
+      (map nixosFor depot.ops.machines.all-systems));
 
   rebuild-system = pkgs.writeShellScriptBin "rebuild-system" ''
     set -ue
@@ -53,9 +40,6 @@ in rec {
   '';
 
   # Systems that should be built in CI
-  #
-  # TODO(tazjin): Refactor the whole systems setup, it's a bit
-  # inconsistent at the moment.
-  whitbySystem = (nixosFor whitby).system;
+  whitbySystem = (nixosFor depot.ops.machines.whitby).system;
   meta.targets = [ "whitbySystem" ];
 }

ops/nixos/.gitignore

@@ -1,3 +0,0 @@
-hardware-configuration.nix
-local-configuration.nix
-result