From 4a89bcd6a5cd409731d7d80fe3dbe364ba00c187 Mon Sep 17 00:00:00 2001
From: Vincent Ambo <mail@tazj.in>
Date: Mon, 24 May 2021 23:29:44 +0200
Subject: refactor(ops/nixos): Pass `depot` as a special argument

This changes the evaluation order for the `depot` argument and ensures
it is partially evaluated before the module system starts resolving
imports.

This way we can import modules from `depot.path` without `depot`
having to come from readTree.

Fixes b/129.

Change-Id: Icf4dd2be15011055dac8b27e991a4ff6a12bf827
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3156
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>
---
 third_party/default.nix | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

(limited to 'third_party/default.nix')

diff --git a/third_party/default.nix b/third_party/default.nix
index 0b1e94c7f86c..5a244ed22039 100644
--- a/third_party/default.nix
+++ b/third_party/default.nix
@@ -17,7 +17,36 @@
 {
   # Expose a partially applied NixOS, expecting an attribute set with
   # a `configuration` key. Exposing it like this makes it possible to
-  # modify some of the base configuration used by NixOS. passed to
-  # this.
-  nixos = import "${pkgs.path}/nixos";
+  # modify some of the base configuration used by NixOS.
+  #
+  # This partially reimplements the code in
+  # <nixpkgs/nixos/default.nix> as we need to modify its internals to
+  # be able to pass `specialArgs`. We depend on this because `depot`
+  # needs to be partially evaluated in NixOS configuration before
+  # module imports are resolved.
+  nixos = {
+    configuration,
+    specialArgs ? {},
+    system ? builtins.currentSystem,
+    ...
+  }:
+  let
+    eval = import "${pkgs.path}/nixos/lib/eval-config.nix" {
+      inherit specialArgs system;
+      modules = [ configuration ];
+    };
+
+    # This is for `nixos-rebuild build-vm'.
+    vmConfig = (import "${pkgs.path}/nixos/lib/eval-config.nix" {
+      inherit specialArgs system;
+      modules = [
+        configuration
+        "${pkgs.path}/nixos/modules/virtualisation/qemu-vm.nix"
+      ];
+    }).config;
+  in {
+    inherit (eval) pkgs config options;
+    system = eval.config.system.build.toplevel;
+    vm = vmConfig.system.build.vm;
+  };
 }
-- 
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