Nix: Some corrections for overlays (#75)

* flake: use legacyPackages for formatter

* nix: separate xdph and share-picker overlays

* flake: make systems overrideable

* flake: inherit packages from overlaid nixpkgs

flake.nix

@@ -4,6 +4,9 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
 
+    # <https://github.com/nix-systems/nix-systems>
+    systems.url = "github:nix-systems/default-linux";
+
     hyprland-protocols = {
       url = "github:hyprwm/hyprland-protocols";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -13,41 +16,28 @@
   outputs = {
     self,
     nixpkgs,
+    systems,
     ...
   } @ inputs: let
     inherit (nixpkgs) lib;
-    genSystems = lib.genAttrs [
-      "aarch64-linux"
-      "x86_64-linux"
-    ];
-    pkgsFor = genSystems (system:
+    eachSystem = lib.genAttrs (import systems);
+    pkgsFor = eachSystem (system:
       import nixpkgs {
-        inherit system;
+        localSystem = system;
         overlays = [
-          self.overlays.default
           inputs.hyprland-protocols.overlays.default
+          self.overlays.xdg-desktop-portal-hyprland
+          self.overlays.hyprland-share-picker
         ];
       });
-    mkDate = longDate: (lib.concatStringsSep "-" [
-      (builtins.substring 0 4 longDate)
-      (builtins.substring 4 2 longDate)
-      (builtins.substring 6 2 longDate)
-    ]);
-    version = "0.pre" + "+date=" + (mkDate (self.lastModifiedDate or "19700101")) + "_" + (self.shortRev or "dirty");
   in {
-    overlays.default = final: prev: {
-      xdg-desktop-portal-hyprland = final.callPackage ./nix/default.nix {
-        inherit (final) hyprland-protocols hyprland-share-picker;
-        inherit version;
-      };
-
-      hyprland-share-picker = final.libsForQt5.callPackage ./nix/hyprland-share-picker.nix {inherit version;};
-    };
+    overlays = import ./nix/overlays.nix {inherit self inputs lib;};
 
-    packages = genSystems (system:
-      (self.overlays.default pkgsFor.${system} pkgsFor.${system})
-      // {default = self.packages.${system}.xdg-desktop-portal-hyprland;});
+    packages = eachSystem (system: {
+      inherit (pkgsFor.${system}) xdg-desktop-portal-hyprland hyprland-share-picker;
+      default = self.packages.${system}.xdg-desktop-portal-hyprland;
+    });
 
-    formatter = genSystems (system: pkgsFor.${system}.alejandra);
+    formatter = eachSystem (system: nixpkgs.legacyPackages.${system}.alejandra);
   };
 }

nix/overlays.nix

@@ -0,0 +1,28 @@
+{
+  self,
+  inputs,
+  lib,
+}: let
+  mkJoinedOverlays = overlays: final: prev:
+    lib.foldl' (attrs: overlay: attrs // (overlay final prev)) {} overlays;
+  mkDate = longDate: (lib.concatStringsSep "-" [
+    (builtins.substring 0 4 longDate)
+    (builtins.substring 4 2 longDate)
+    (builtins.substring 6 2 longDate)
+  ]);
+  version = "0.pre" + "+date=" + (mkDate (self.lastModifiedDate or "19700101")) + "_" + (self.shortRev or "dirty");
+in {
+  default = mkJoinedOverlays (with self.overlays; [
+    xdg-desktop-portal-hyprland
+    hyprland-share-picker
+  ]);
+  xdg-desktop-portal-hyprland = final: prev: {
+    xdg-desktop-portal-hyprland = final.callPackage ./default.nix {
+      inherit (final) hyprland-protocols hyprland-share-picker;
+      inherit version;
+    };
+  };
+  hyprland-share-picker = final: prev: {
+    hyprland-share-picker = final.libsForQt5.callPackage ./hyprland-share-picker.nix {inherit version;};
+  };
+}