support for patching nixpkgs instance used by home manager

- introduce support for patching the used nixpkgs instance via
  `applyPatches`, see https://ertt.ca/nix/patch-nixpkgs/
- use patched nixpkgs instance in mkHomeManagern (TODO: use it in more
  places)
- add patch for nodejs-20 test failure in darwin (currently just in
  staging)

flake.nix

@@ -46,6 +46,16 @@
     let
       # FIXME: allow different systems
       systems = utils.lib.system;
+
+      # ability to extend nixpkgs with patches, e.g. from PRs or staging. See https://ertt.ca/nix/patch-nixpkgs/
+      mkNixpkgs-patched =
+        system:
+        (import nixpkgs { inherit system; }).applyPatches {
+          name = "nixpkgs-patched";
+          src = nixpkgs;
+          patches = [ ./patches/nixos-nixpkgs-362c2bc76d359b908ad1389ee28c23ee0e862324.patch ];
+        };
+
       # necessary to make the top-level inputs available to system configuration
       # inspired by https://jade.fyi/blog/flakes-arent-real/
       inputInjection =
@@ -78,7 +88,7 @@
       mkHomeManager =
         confName: user: system: # unfortunately, home-manager configs are still system-specific
         home-manager.lib.homeManagerConfiguration {
-          pkgs = nixpkgs.legacyPackages.${system};
+          pkgs = import (mkNixpkgs-patched system) { inherit system; };
           modules = [
             {
               imports = [

patches/nixos-nixpkgs-362c2bc76d359b908ad1389ee28c23ee0e862324.patch

@@ -0,0 +1,26 @@
+From 362c2bc76d359b908ad1389ee28c23ee0e862324 Mon Sep 17 00:00:00 2001
+From: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>
+Date: Mon, 7 Apr 2025 21:03:09 -0400
+Subject: [PATCH] nodejs_20: fix test failure on darwin on latest MacOS 15.4
+
+Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>
+(cherry picked from commit 9674c1f688d12b99fbde26e6068ab62609fef3b1)
+---
+ pkgs/development/web/nodejs/v20.nix | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/pkgs/development/web/nodejs/v20.nix b/pkgs/development/web/nodejs/v20.nix
+index b9c9345c441afa..20cceb5b5d1cda 100644
+--- a/pkgs/development/web/nodejs/v20.nix
++++ b/pkgs/development/web/nodejs/v20.nix
+@@ -50,5 +50,10 @@ buildNodejs {
+       stripLen = 1;
+       hash = "sha256-6y3aEqxNC4iTQEv1oewodJrhOHxjp5xZMq1P1QL94Rg=";
+     })
++    # fix test failure on macos 15.4
++    (fetchpatch2 {
++      url = "https://github.com/nodejs/node/commit/33f6e1ea296cd20366ab94e666b03899a081af94.patch?full_index=1";
++      hash = "sha256-aVBMcQlhQeviUQpMIfC988jjDB2BgYzlMYsq+w16mzU=";
++    })
+   ] ++ gypPatches;
+ }