Change installation instructions to use nix-channel

This avoids the uncontrollable nature of fetching the tarball as part
of the evaluation. Instead the user can decide when to update and also
perform rollbacks, if necessary.

(cherry picked from commit a37b5c9c61)

.travis.yml

@@ -6,8 +6,6 @@ os:
 
 before_script:
   - mkdir -m 0755 -p /nix/var/nix/{profiles,gcroots}/per-user/$USER
-  - mkdir -p ~/.config/nixpkgs
-  - echo "{}" > ~/.config/nixpkgs/home.nix
 
 script:
   nix-shell . -A install

README.md

@@ -54,42 +54,32 @@ Currently the easiest way to install Home Manager is as follows:
     NixOS you can control this option using the
     [`nix.allowedUsers`][nixosAllowedUsers] system option.
 
-2.  Assign a temporary variable holding the URL to the appropriate
+2.  Add the appropriate Home Manager channel. Typically this is
-    archive. Typically this is
 
     ```console
-    $ HM_PATH=https://github.com/rycee/home-manager/archive/master.tar.gz
+    $ nix-channel --add https://github.com/rycee/home-manager/archive/master.tar.gz home-manager
+    $ nix-channel --update
     ```
 
     if you are following Nixpkgs master or an unstable channel and
 
     ```console
-    $ HM_PATH=https://github.com/rycee/home-manager/archive/release-18.09.tar.gz
+    $ nix-channel --add https://github.com/rycee/home-manager/archive/release-18.09.tar.gz home-manager
+    $ nix-channel --update
     ```
 
     if you follow a Nixpkgs version 18.09 channel.
 
-3.  Create an initial Home Manager configuration file:
+3.  Install Home Manager and create the first Home Manager generation:
 
     ```console
-    $ cat > ~/.config/nixpkgs/home.nix <<EOF
+    $ nix-shell '<home-manager>' -A install
-    {
-      programs.home-manager.enable = true;
-      programs.home-manager.path = $HM_PATH;
-    }
-    EOF
     ```
 
-4.  Install Home Manager and create the first Home Manager generation:
+    Once finished, Home Manager should be active and available in your
+    user environment.
 
-    ```console
+3.  If you do not plan on having Home Manager manage your shell
-    $ nix-shell $HM_PATH -A install
-    ```
-
-    Home Manager should now be active and available in your user
-    environment.
-
-5.  If you do not plan on having Home Manager manage your shell
     configuration then you must source the
 
     ```
@@ -107,11 +97,10 @@ Currently the easiest way to install Home Manager is as follows:
 
     to your `~/.profile` file.
 
-Note, because the `HM_PATH` variable above points to the live Home
+If instead of using channels you want to run Home Manager from a Git
-Manager repository you will automatically get updates whenever you
+checkout of the repository then you can use the
-build a new generation. If you dislike automatic updates then perform
+`programs.home-manager.path` option to specify the absolute path to
-a Git clone of the desired branch and instead do the above steps with
+the repository.
-`HM_PATH` set to the _absolute path_ of your clone.
 
 Usage
 -----

home-manager/install.nix

@@ -7,6 +7,23 @@ pkgs.runCommand
     preferLocalBuild = true;
     allowSubstitutes = false;
     shellHook = ''
+      confFile="''${XDG_CONFIG_HOME:-$HOME/.config}/nixpkgs/home.nix"
+
+      if [[ ! -e $confFile ]]; then
+        echo
+        echo "Creating initial Home Manager configuration..."
+
+        mkdir -p "$(dirname "$confFile")"
+        cat > $confFile <<EOF
+      { config, pkgs, ... }:
+
+      {
+        # Let Home Manager install and manage itself.
+        programs.home-manager.enable = true;
+      }
+      EOF
+      fi
+
       echo
       echo "Creating initial Home Manager generation..."
       echo
@@ -17,7 +34,7 @@ pkgs.runCommand
       All done! The home-manager tool should now be installed and you
       can edit
 
-          ''${XDG_CONFIG_HOME:-~/.config}/nixpkgs/home.nix
+          $confFile
 
       to configure Home Manager. Run 'man home-configuration.nix' to
       see all available options.