nix: make all files self-contained

nix/overlays/default.nix

@@ -1,41 +1,40 @@
-{
-  sources,
-  lib,
-  ...
-}:
-lib.composeManyExtensions [
-  (final: _: {
-    # Isabelle version 2023
-    inherit (import sources.isabelle-pin {}) isabelle;
+let
+  sources = import ../sources.nix;
+  lib = import (sources.nixpkgs + "/lib");
+in
+  lib.composeManyExtensions [
+    (final: _: {
+      # Isabelle version 2023
+      inherit (import sources.isabelle-pin {}) isabelle;
 
-    # Wireshark bug
-    # https://gitlab.com/wireshark/wireshark/-/issues/19574
-    inherit (import sources.wireshark-pin {}) wireshark;
+      # Wireshark bug
+      # https://gitlab.com/wireshark/wireshark/-/issues/19574
+      inherit (import sources.wireshark-pin {}) wireshark;
 
-    inherit (import sources.digikam-pin {}) digikam;
+      inherit (import sources.digikam-pin {}) digikam;
 
-    wallpapers = final.callPackage sources.wallpapers {};
+      wallpapers = final.callPackage sources.wallpapers {};
 
-    # Boomer has no flake-compat built-in, so let's hack it
-    boomer = let
-      flake-compat = import sources.flake-compat;
-      boomer-flake = (flake-compat {src = sources.boomer;}).defaultNix;
-    in
-      boomer-flake.packages.${final.system}.default;
+      # Boomer has no flake-compat built-in, so let's hack it
+      boomer = let
+        flake-compat = import sources.flake-compat;
+        boomer-flake = (flake-compat {src = sources.boomer;}).defaultNix;
+      in
+        boomer-flake.packages.${final.system}.default;
 
-    inherit (final.callPackage sources.agenix {}) agenix;
+      inherit (final.callPackage sources.agenix {}) agenix;
 
-    disko =
-      final.callPackage (sources.disko + "/package.nix")
-      {diskoVersion = sources.disko.version;};
-  })
+      disko =
+        final.callPackage (sources.disko + "/package.nix")
+        {diskoVersion = sources.disko.version;};
+    })
 
-  (_: prev: {
-    nur = import sources.nur {
-      nurpkgs = prev;
-      pkgs = prev;
-    };
-  })
+    (_: prev: {
+      nur = import sources.nur {
+        nurpkgs = prev;
+        pkgs = prev;
+      };
+    })
 
-  ((import sources.wired-notify).overlays.default)
-]
+    ((import sources.wired-notify).overlays.default)
+  ]

nix/overlays/packagesStable.nix

@@ -1,6 +1,9 @@
-{sources, ...}: _: _: {
-  myPkgs = let
-    pkgs = import sources.nixpkgs-stable {};
-  in
-    pkgs.callPackages ../packages {};
-}
+let
+  sources = import ../sources.nix;
+in
+  _: _: {
+    myPkgs = let
+      pkgs = import sources.nixpkgs-stable {};
+    in
+      pkgs.callPackages ../packages {};
+  }