From 8dc8fa38b0d17953d0d760d3ac267e154f7b1497 Mon Sep 17 00:00:00 2001
From: Matt Sturgeon <matt@sturgeon.me.uk>
Date: Sat, 19 Oct 2024 23:45:28 +0100
Subject: [PATCH] modules/nixpkgs: add `hostPlatform` & `buildPlatform` options

---
 modules/top-level/nixpkgs.nix | 46 +++++++++++++++++++++++++++++++++++
 wrappers/_shared.nix          | 15 +++++++++---
 2 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/modules/top-level/nixpkgs.nix b/modules/top-level/nixpkgs.nix
index 0b8151fe..3827f2d0 100644
--- a/modules/top-level/nixpkgs.nix
+++ b/modules/top-level/nixpkgs.nix
@@ -172,6 +172,52 @@ in
       '';
     };
 
+    hostPlatform = lib.mkOption {
+      type = with lib.types; either str attrs;
+      example = {
+        system = "aarch64-linux";
+      };
+      apply = lib.systems.elaborate;
+      defaultText = lib.literalMD ''
+        - Inherited from the "host" configuration's `pkgs`
+        - Must be specified manually when building a standalone nixvim
+      '';
+      description = ''
+        Specifies the platform where the Nixvim configuration will run.
+
+        To cross-compile, also set `nixpkgs.buildPlatform`.
+
+        Ignored when `nixpkgs.pkgs` is set.
+      '';
+    };
+
+    buildPlatform = lib.mkOption {
+      type = with lib.types; either str attrs;
+      default = cfg.hostPlatform;
+      example = {
+        system = "x86_64-linux";
+      };
+      apply =
+        value:
+        let
+          elaborated = lib.systems.elaborate value;
+        in
+        # If equivalent to `hostPlatform`, make it actually identical so that `==` can be used
+        # See https://github.com/NixOS/nixpkgs/issues/278001
+        if lib.systems.equals elaborated cfg.hostPlatform then cfg.hostPlatform else elaborated;
+      defaultText = lib.literalMD ''
+        Inherited from the "host" configuration's `pkgs`.
+        Or `config.nixpkgs.hostPlatform` when building a standalone nixvim.
+      '';
+      description = ''
+        Specifies the platform on which Nixvim should be built.
+        By default, Nixvim is built on the system where it runs, but you can change where it's built.
+        Setting this option will cause Nixvim to be cross-compiled.
+
+        Ignored when `nixpkgs.pkgs` is set.
+      '';
+    };
+
     # NOTE: This is a nixvim-specific option; there's no equivalent in nixos
     source = lib.mkOption {
       type = lib.types.path;
diff --git a/wrappers/_shared.nix b/wrappers/_shared.nix
index 33c002b6..424c4c82 100644
--- a/wrappers/_shared.nix
+++ b/wrappers/_shared.nix
@@ -32,11 +32,20 @@ let
     evalArgs
     // {
       modules = evalArgs.modules or [ ] ++ [
-        # Use global packages by default in nixvim's submodule
-        # TODO: `useGlobalPackages` option and/or deprecate using host packages?
         {
           _file = ./_shared.nix;
-          nixpkgs.pkgs = lib.mkDefault pkgs;
+
+          nixpkgs = {
+            # Use global packages by default in nixvim's submodule
+            # TODO: `useGlobalPackages` option and/or deprecate using host packages?
+            pkgs = lib.mkDefault pkgs;
+
+            # Inherit platform spec
+            # FIXME: buildPlatform can't use option-default because it already has a default
+            #        (it defaults to hostPlatform)...
+            hostPlatform = lib.mkOptionDefault pkgs.stdenv.hostPlatform;
+            buildPlatform = lib.mkDefault pkgs.stdenv.buildPlatform;
+          };
         }
       ];
     }