nixpkgs: take Nixpkgs path from argument

This removes the dependency on the `nixpkgs` channel within the
modules for state version ≥ 20.09. The default Nixpkgs source starting
from this state version is the path of the `pkgs` argument used to
bootstrap the Home Manager modeuls.

This is a prerequisite for using Home Manager withing Nix flakes.

PR #1420

2 files changed, 8 insertions, 3 deletions

diff --git a/modules/misc/nixpkgs.nix b/modules/misc/nixpkgs.nix
index 7b0904a5f20..511dbec10b2 100644
--- a/modules/misc/nixpkgs.nix
+++ b/modules/misc/nixpkgs.nix
@@ -1,6 +1,6 @@
 # Adapted from Nixpkgs.
 
-{ config, lib, pkgs, ... }:
+{ config, lib, pkgs, pkgsPath, ... }:
 
 with lib;
 
@@ -49,7 +49,7 @@ let
     merge = lib.mergeOneOption;
   };
 
-  _pkgs = import <nixpkgs> (
+  _pkgs = import pkgsPath (
     filterAttrs (n: v: v != null) config.nixpkgs
   );
 
diff --git a/modules/modules.nix b/modules/modules.nix
index 1744b4fd096..fa9c7f38cb7 100644
--- a/modules/modules.nix
+++ b/modules/modules.nix
@@ -197,9 +197,14 @@ let
 
   modules = map (getAttr "file") (filter (getAttr "condition") allModules);
 
-  pkgsModule = {
+  pkgsModule = { config, ... }: {
     config = {
       _module.args.baseModules = modules;
+      _module.args.pkgsPath = lib.mkDefault (
+        if versionAtLeast config.home.stateVersion "20.09" then
+          pkgs.path
+        else
+          <nixpkgs>);
       _module.args.pkgs = lib.mkDefault pkgs;
       _module.check = check;
       lib = lib.hm;