From 30b53c8f72db7da42fbbdb862460228f803afb83 Mon Sep 17 00:00:00 2001
From: Sridhar Ratnakumar <srid@srid.ca>
Date: Thu, 22 Feb 2024 13:55:43 -0500
Subject: [PATCH] darwin: add linux builder

---
 flake.lock            | 11 ++++++-----
 flake.nix             |  4 +++-
 systems/darwin/ci.nix | 29 +++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 6 deletions(-)
 create mode 100644 systems/darwin/ci.nix

diff --git a/flake.lock b/flake.lock
index fb531171..fa09a5cf 100644
--- a/flake.lock
+++ b/flake.lock
@@ -914,15 +914,16 @@
         ]
       },
       "locked": {
-        "lastModified": 1708231718,
-        "narHash": "sha256-IZdieFWvhBkxoOFMDejqLUYqD94WN6k0YSpw0DFy+4g=",
-        "owner": "lnl7",
+        "lastModified": 1708541070,
+        "narHash": "sha256-dhi3XXT662o1FtP/Li2dIwcQCco6nhT+Yv71dptTlSw=",
+        "owner": "LoganBarnett",
         "repo": "nix-darwin",
-        "rev": "0e6857fa1d632637488666c08e7b02c08e3178f8",
+        "rev": "27e6a022f25b94010fdb8e5fbbb79608dc589397",
         "type": "github"
       },
       "original": {
-        "owner": "lnl7",
+        "owner": "LoganBarnett",
+        "ref": "linux-builder-big-config",
         "repo": "nix-darwin",
         "type": "github"
       }
diff --git a/flake.nix b/flake.nix
index 8902f448..2423a682 100644
--- a/flake.nix
+++ b/flake.nix
@@ -5,7 +5,8 @@
     # Principle inputs
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
     flake-parts.url = "github:hercules-ci/flake-parts";
-    nix-darwin.url = "github:lnl7/nix-darwin";
+    # nix-darwin.url = "github:lnl7/nix-darwin";
+    nix-darwin.url = "github:LoganBarnett/nix-darwin/linux-builder-big-config"; # https://github.com/LnL7/nix-darwin/pull/878 (for 'systems')
     nix-darwin.inputs.nixpkgs.follows = "nixpkgs";
     home-manager.url = "github:nix-community/home-manager";
     home-manager.inputs.nixpkgs.follows = "nixpkgs";
@@ -113,6 +114,7 @@
             imports = [
               self.darwinModules.default # Defined in nix-darwin/default.nix
               ./systems/darwin.nix
+              ./systems/darwin/ci.nix
             ];
           };
           naivete = self.nixos-flake.lib.mkMacosSystem {
diff --git a/systems/darwin/ci.nix b/systems/darwin/ci.nix
new file mode 100644
index 00000000..6a60f891
--- /dev/null
+++ b/systems/darwin/ci.nix
@@ -0,0 +1,29 @@
+{ ... }:
+
+{
+  # TODO: GitHub Runners
+
+  # To build Linux derivations whilst on macOS.
+  # 
+  # NOTES:
+  # - To SSH, `sudo su -` and then `ssh -i /etc/nix/builder_ed25519  builder@linux-builder`.
+  #   Unfortunately, a simple `ssh linux-builder` will not work (Too many authentication failures).
+  # - To update virtualisation configuration, you have to disable, delete
+  #   /private/var/lib/darwin-builder/ and re-enable.
+  nix.linux-builder = {
+    enable = true;
+    systems = [
+      "x86_64-linux"
+      "aarch64-linux"
+    ];
+    config = { pkgs, lib, ... }: {
+      boot.binfmt.emulatedSystems = [ "x86_64-linux" ];
+      virtualisation = {
+        # Larger linux-builder cores, ram, and disk.
+        cores = 6;
+        memorySize = lib.mkForce (1024 * 16);
+        diskSize = lib.mkForce (1024 * 1); # In MB.
+      };
+    };
+  };
+}