pkgs: call nixpkgs entrypoint outside of config

By moving this call under our control, we can insert our own default
Nixpkgs arguments, for example overlays, or maybe crossSystem.

Signed-off-by: Alyssa Ross <hi@alyssa.is>

3 files changed, 19 insertions, 12 deletions

diff --git a/Documentation/development/build-configuration.adoc b/Documentation/development/build-configuration.adoc
index 4f7d8e9..545aa8c 100644
--- a/Documentation/development/build-configuration.adoc
+++ b/Documentation/development/build-configuration.adoc
@@ -4,6 +4,7 @@
 :example-caption: Test
 
 // SPDX-FileCopyrightText: 2022 Unikie
+// SPDX-FileCopyrightText: 2023 Alyssa Ross <hi@alyssa.is>
 // SPDX-License-Identifier: GFDL-1.3-no-invariants-or-later OR CC-BY-SA-4.0
 
 Some aspects of a Spectrum build can be customised using a build
@@ -15,9 +16,9 @@ the root of the Spectrum source tree, but this can be overridden by setting
 https://nixos.org/manual/nix/stable/command-ref/env-common.html#env-NIX_PATH[NIX_PATH]
 to the path of the configuration file.
 
-The configuration file should contain an attribute set.  The only
-currently allowed attribute name is `pkgs`. It allows using a
-custom Nixpkgs to evaluate Spectrum.
+The configuration file should contain an attribute set.  See
+https://spectrum-os.org/git/spectrum/tree/lib/config.default.nix[lib/config.default.nix]
+for supported configuration attributes and their default values.
 
 .config.nix to build Spectrum with a https://nixos.org/manual/nixpkgs/unstable/#sec-overlays-definition[Nixpkgs overlay]
 [example]
@@ -26,12 +27,16 @@ custom Nixpkgs to evaluate Spectrum.
 { default, ... }:
 
 {
-  pkgs = default.pkgs.extend (final: super: {
-    weston = super.weston.overrideAttrs ({ patches ? [], ... }: {
-      patches = patches ++ [
-        path/to/weston.patch
-      ];
-    });
-  });
+  pkgsArgs = default.pkgsArgs // {
+    overlays = [
+      (final: super: {
+        weston = super.weston.overrideAttrs ({ patches ? [], ... }: {
+          patches = patches ++ [
+            path/to/weston.patch
+          ];
+        });
+      })
+    ] ++ default.pkgsArgs.overlays or [];
+  };
 }
 ----
diff --git a/lib/config.default.nix b/lib/config.default.nix
index af01756..a842234 100644
--- a/lib/config.default.nix
+++ b/lib/config.default.nix
@@ -2,5 +2,6 @@
 # SPDX-License-Identifier: MIT
 
 {
-  pkgs = import ./nixpkgs.default.nix {};
+  pkgsFun = import ./nixpkgs.default.nix;
+  pkgsArgs = {};
 }
diff --git a/pkgs/default.nix b/pkgs/default.nix
index 96a31f4..aec09b5 100644
--- a/pkgs/default.nix
+++ b/pkgs/default.nix
@@ -20,7 +20,8 @@ let
 
   fullConfig = default // callConfig config;
 
-  inherit (fullConfig) pkgs;
+  pkgs = fullConfig.pkgsFun fullConfig.pkgsArgs;
+
   inherit (pkgs.lib)
     cleanSource cleanSourceWith hasSuffix makeScope optionalAttrs;