home-manager: point <home-manager> to project root

Before this path would point to the modules path. Using the project
root instead makes it possible to set `<home-manager>` to point to a
downloadable archive of Home Manager. This should make it
significantly easier to install and keep Home Manager up to date.

To match this change we also deprecate the Home Manager option

    programs.home-manager.modulesPath

and instead ask users to use

    programs.home-manager.path

default.nix

@@ -1,2 +1,14 @@
-# Simply defer to the home-manager script derivation.
-import ./home-manager
+{ pkgs ? import <nixpkgs> {} }:
+
+rec {
+  home-manager = import ./home-manager {
+    inherit pkgs;
+    path = ./.;
+  };
+
+  install =
+    pkgs.runCommand
+      "home-manager-install"
+      { propagatedBuildInputs = [ home-manager ]; }
+      "";
+}

home-manager/default.nix

@@ -1,14 +1,14 @@
 { pkgs
 
-  # Extra path to the Home Manager modules. If set then this path will
-  # be tried before `$HOME/.config/nixpkgs/home-manager/modules` and
-  # `$HOME/.nixpkgs/home-manager/modules`.
-, modulesPath ? null
+  # Extra path to Home Manager. If set then this path will be tried
+  # before `$HOME/.config/nixpkgs/home-manager` and
+  # `$HOME/.nixpkgs/home-manager`.
+, path ? null
 }:
 
 let
 
-  modulesPathStr = if modulesPath == null then "" else modulesPath;
+  pathStr = if path == null then "" else path;
 
 in
 
@@ -24,8 +24,7 @@ pkgs.stdenv.mkDerivation {
       --subst-var-by bash "${pkgs.bash}" \
       --subst-var-by coreutils "${pkgs.coreutils}" \
       --subst-var-by less "${pkgs.less}" \
-      --subst-var-by MODULES_PATH '${modulesPathStr}' \
-      --subst-var-by HOME_MANAGER_EXPR_PATH "${./home-manager.nix}"
+      --subst-var-by HOME_MANAGER_PATH '${pathStr}'
   '';
 
   meta = with pkgs.stdenv.lib; {

home-manager/home-manager

@@ -40,13 +40,13 @@ function setConfigFile() {
     exit 1
 }
 
-function setHomeManagerModulesPath() {
-    local modulesPath
-    for modulesPath in "@MODULES_PATH@" \
-                       "$HOME/.config/nixpkgs/home-manager/modules" \
-                       "$HOME/.nixpkgs/home-manager/modules" ; do
-        if [[ -e "$modulesPath" ]] ; then
-            export NIX_PATH="$NIX_PATH${NIX_PATH:+:}home-manager=$modulesPath"
+function setHomeManagerNixPath() {
+    local path
+    for path in "@HOME_MANAGER_PATH@" \
+                "$HOME/.config/nixpkgs/home-manager" \
+                "$HOME/.nixpkgs/home-manager" ; do
+        if [[ -e "$path" || "$path" =~ ^https?:// ]] ; then
+            export NIX_PATH="$NIX_PATH${NIX_PATH:+:}home-manager=$path"
             return
         fi
     done
@@ -54,7 +54,7 @@ function setHomeManagerModulesPath() {
 
 function doBuildAttr() {
     setConfigFile
-    setHomeManagerModulesPath
+    setHomeManagerNixPath
 
     local extraArgs="$*"
 
@@ -67,7 +67,7 @@ function doBuildAttr() {
     fi
 
     nix-build \
-        "@HOME_MANAGER_EXPR_PATH@" \
+        "<home-manager/home-manager/home-manager.nix>" \
         $extraArgs \
         --argstr confPath "$HOME_MANAGER_CONFIG" \
         --argstr confAttr "$HOME_MANAGER_CONFIG_ATTRIBUTE"

home-manager/home-manager.nix

@@ -9,7 +9,7 @@ with pkgs.lib;
 
 let
 
-  env = import <home-manager> {
+  env = import <home-manager/modules> {
     configuration =
       let
         conf = import confPath;

modules/misc/news.nix

@@ -370,6 +370,46 @@ in
           chosen version.
         '';
       }
+
+      {
+        time = "2017-10-23T22:54:33+00:00";
+        condition = config.programs.home-manager.modulesPath != null;
+        message = ''
+          The 'programs.home-manager.modulesPath' option is now
+          deprecated and will be removed on November 24, 2017. Please
+          use the option 'programs.home-manager.path' instead.
+        '';
+      }
+
+      {
+        time = "2017-10-23T23:10:29+00:00";
+        condition = !config.programs.home-manager.enable;
+        message = ''
+          Unfortunately, due to some internal restructuring it is no
+          longer possible to install the home-manager command when
+          having
+
+              home-manager = import ./home-manager { inherit pkgs; };
+
+          in the '~/.config/nixpkgs/config.nix' package override
+          section. Attempting to use the above override will now
+          result in the error "cannot coerce a set to a string".
+
+          To resolve this please delete the override from the
+          'config.nix' file and either link the Home Manager overlay
+
+              $ ln -s ~/.config/nixpkgs/home-manager/overlay.nix \
+                      ~/.config/nixpkgs/overlays/home-manager.nix
+
+          or add
+
+              programs.home-manager.enable = true;
+
+          to your Home Manager configuration. The latter is
+          recommended as the home-manager tool then is updated
+          automatically whenever you do a switch.
+        '';
+      }
     ];
   };
 }

modules/programs/home-manager.nix

@@ -16,6 +16,19 @@ in
     programs.home-manager = {
       enable = mkEnableOption "Home Manager";
 
+      path = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        example = "$HOME/devel/home-manager";
+        description = ''
+          The default path to use for Home Manager. If this path does
+          not exist then
+          <filename>$HOME/.config/nixpkgs/home-manager</filename> and
+          <filename>$HOME/.nixpkgs/home-manager</filename> will be
+          attempted.
+        '';
+      };
+
       modulesPath = mkOption {
         type = types.nullOr types.str;
         default = null;
@@ -25,17 +38,28 @@ in
           path does not exist then
           <filename>$HOME/.config/nixpkgs/home-manager/modules</filename>
           and <filename>$HOME/.nixpkgs/home-manager/modules</filename>
-          will be attempted.
+          will be attempted. DEPRECATED: Use
+          <varname>programs.home-manager.path</varname> instead.
         '';
       };
     };
   };
 
   config = mkIf cfg.enable {
+    assertions = [{
+      assertion = cfg.path == null || cfg.modulesPath == null;
+      message = "Cannot simultaneously use "
+        + "'programs.home-manager.path' and "
+        + "'programs.home-manager.modulesPath'.";
+    }];
+
     home.packages = [
       (import ../../home-manager {
         inherit pkgs;
-        inherit (cfg) modulesPath;
+        path =
+          if cfg.modulesPath != null
+          then "$(dirname ${cfg.modulesPath})"
+          else cfg.path;
       })
     ];