core: migrate to flakes

flake.nix

@@ -0,0 +1,34 @@
+{
+  description = "xeals's flake";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    let
+      inherit (flake-utils.lib) defaultSystems flattenTree;
+      inherit (nixpkgs.lib.attrsets) filterAttrs genAttrs mapAttrs;
+    in
+    {
+      nixosModules = mapAttrs (_: path: import path) (import ./modules);
+      overlay = final: prev: {
+        xeals = nixpkgs.lib.composeExtensions self.overlays.pkgs;
+      };
+      overlays = import ./overlays // {
+        pkgs = final: prev: import ./pkgs/top-level/all-packages.nix { pkgs = prev; };
+      };
+      packages = genAttrs defaultSystems
+        (system:
+          let
+            pkgs = nixpkgs.legacyPackages.${system};
+            xPkgs = import ./pkgs/top-level/all-packages.nix { inherit pkgs; };
+          in
+          filterAttrs
+            (attr: drv:
+              builtins.elem system drv.meta.platforms or [ ])
+            xPkgs
+        );
+    };
+}