extract & rework backports overlay

flake.nix

@@ -100,6 +100,8 @@
 
       nixosModules = importFlakeMod ./nix/nixos-modules;
 
+      overlays = importFlakeMod ./nix/overlays;
+
       packages = importFlakeModWithSystem ./nix/packages;
 
     };

nix/nixos-modules/default.nix

@@ -49,14 +49,7 @@
         outputs.nixosModules.banananetwork
       ];
       config = {
-        nixpkgs.overlays = [
+        nixpkgs.overlays = lib.singleton outputs.overlays.backports;
-          # TODO until 24.11
-          (lib.mkIf (!lib.versionAtLeast lib.version "24.11") (
-            final: prev: {
-              inherit ((lib.systemSpecificVars pkgs.system).pkgs_unstable) nixfmt-rfc-style wcurl;
-            }
-          ))
-        ];
       };
     };
 

nix/overlays/backports.nix

@@ -0,0 +1,20 @@
+{ lib, ... }@flakeArg:
+{ pkgs_unstable, ... }@systemArg:
+final: prev:
+let
+  list = [
+    # TODO until 24.11
+    "nixfmt-rfc-style"
+    "wcurl"
+  ];
+  backport =
+    pkgAttrName:
+    let
+      alreadyStable = builtins.hasAttr pkgAttrName prev;
+      stableSource = lib.warn "consider removing ${pkgAttrName} from backports list as it is now available on stable" prev;
+      source = if alreadyStable then stableSource else pkgs_unstable;
+      pkg = builtins.getAttr pkgAttrName source;
+    in
+    pkg;
+in
+lib.genAttrs list backport

nix/overlays/default.nix

@@ -0,0 +1,14 @@
+{ lib, ... }@flakeArg:
+let
+  inherit (lib) systemSpecificVars;
+  rawImport = path: import path flakeArg;
+  wrapOverlay =
+    overlay: final: prev:
+    overlay (systemSpecificVars prev.system) final prev;
+  importOverlay = path: wrapOverlay (rawImport path);
+in
+{
+
+  backports = importOverlay ./backports.nix;
+
+}