home-manger: fix runtime closure (#5174)

Without this fix a `nix-buid . -A home-manager` would successfully
create a `home-manager`. And one could use the included binary until
the next garbage collection, after that it would fail with an
error that it can not find the `home-manager` sources.

Similarily a `nix-copy-closure`d `home-manager` would fail with the
same error on the copies target machine.

This problem existed on both, the flake as well as the non-flake build
of `home-manager`.

default.nix

@@ -1,6 +1,12 @@
 { pkgs ? import <nixpkgs> { } }:
 
-rec {
+let
+  path = builtins.path {
+    path = ./.;
+    name = "home-manager-source";
+  };
+
+in rec {
   docs = let releaseInfo = pkgs.lib.importJSON ./release.json;
   in with import ./docs {
     inherit pkgs;
@@ -12,12 +18,12 @@ rec {
     jsonModuleMaintainers = jsonModuleMaintainers; # Unstable, mainly for CI.
   };
 
-  home-manager = pkgs.callPackage ./home-manager { path = toString ./.; };
+  home-manager = pkgs.callPackage ./home-manager { inherit path; };
 
   install =
     pkgs.callPackage ./home-manager/install.nix { inherit home-manager; };
 
   nixos = import ./nixos;
 
-  path = ./.;
+  inherit path;
 }

flake.nix

@@ -104,7 +104,7 @@
             inherit pkgs;
             inherit (releaseInfo) release isReleaseBranch;
           };
-          hmPkg = pkgs.callPackage ./home-manager { path = "${./.}"; };
+          hmPkg = pkgs.callPackage ./home-manager { path = "${self}"; };
         in {
           default = hmPkg;
           home-manager = hmPkg;