lib: create 'my' extensions

Inspired by this [1] repo, I want to add some functions to `lib.my`. I
would have liked to make it work without having to use an overlay, but I
did not manage to do it...

[1]: https://github.com/hlissner/dotfiles

flake.nix

@@ -8,11 +8,14 @@
     futils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs, nur, home-manager, futils }:
+  outputs = { self, nixpkgs, nur, home-manager, futils } @ inputs:
     let
-      inherit (nixpkgs) lib;
       inherit (futils.lib) eachDefaultSystem;
 
+      lib = nixpkgs.lib.extend (self: super: {
+        my = import ./lib { inherit inputs; pkgs = nixpkgs; lib = self; };
+      });
+
       defaultModules = [
         ({ ... }: {
           # Let 'nixos-version --json' know about the Git revision
@@ -21,7 +24,7 @@
             then self.rev
             else throw "Refusing to build from a dirty Git tree!";
         })
-        { nixpkgs.overlays = [ nur.overlay ]; }
+        { nixpkgs.overlays = [ nur.overlay self.overlay ]; }
         home-manager.nixosModules.home-manager
         {
           home-manager.users.ambroisie = import ./home;
@@ -52,6 +55,12 @@
             ];
           };
         }) // {
+      overlay = self.overlays.lib;
+
+      overlays = {
+        lib = final: prev: { inherit lib; };
+      };
+
       nixosConfigurations = lib.mapAttrs buildHost {
         porthos = "x86_64-linux";
       };

lib/attrs.nix

@@ -0,0 +1,7 @@
+{ lib, ... }:
+let
+  inherit (lib) filterAttrs mapAttrs';
+in
+{
+  mapFilterAttrs = pred: f: attrs: filterAttrs pred (mapAttrs' f attrs);
+}

lib/default.nix

@@ -0,0 +1,21 @@
+# Extension mechanism shamelessly stolen from [1].
+#
+# [1]: https://github.com/hlissner/dotfiles/blob/master/lib/default.nix
+{ lib, pkgs, inputs }:
+let
+  inherit (lib) makeExtensible attrValues foldr;
+  inherit (modules) mapModules;
+
+  modules = import ./modules.nix {
+    inherit lib;
+    self.attrs = import ./attrs.nix { inherit lib; self = { }; };
+  };
+
+  mylib = makeExtensible (self:
+    with self; mapModules ./.
+      (file: import file { inherit self lib pkgs inputs; })
+  );
+in
+mylib.extend (self: super:
+  foldr (a: b: a // b) { } (attrValues super)
+)

lib/modules.nix

@@ -0,0 +1,23 @@
+{ self, lib, ... }:
+let
+  inherit (builtins) readDir pathExists;
+  inherit (lib) hasPrefix hasSuffix nameValuePair removeSuffix;
+  inherit (self.attrs) mapFilterAttrs;
+in
+{
+  mapModules = dir: fn:
+    mapFilterAttrs
+      (n: v:
+        v != null &&
+        !(hasPrefix "_" n))
+      (n: v:
+        let path = "${toString dir}/${n}"; in
+        if v == "directory" && pathExists "${path}/default.nix"
+        then nameValuePair n (fn path)
+        else if v == "regular" &&
+          n != "default.nix" &&
+          hasSuffix ".nix" n
+        then nameValuePair (removeSuffix ".nix" n) (fn path)
+        else nameValuePair "" null)
+      (readDir dir);
+}