home-manager: Add home-manager search path to EXTRA_NIX_PATH (#3241)

docs/installation.adoc

@@ -58,16 +58,6 @@ and if you follow a Nixpkgs version 22.11 channel you can run
 $ nix-channel --add https://github.com/nix-community/home-manager/archive/release-22.11.tar.gz home-manager
 $ nix-channel --update
 ----
-+
-On non-NixOS, you may have to add
-+
-[source,bash]
-export NIX_PATH=$HOME/.nix-defexpr/channels:/nix/var/nix/profiles/per-user/root/channels${NIX_PATH:+:$NIX_PATH}
-+
-to your shell (see https://github.com/NixOS/nix/issues/2033[nix#2033]
-and
-https://discourse.nixos.org/t/where-is-nix-path-supposed-to-be-set/16434/8[this
-reply on the Nix Discourse]).
 
 3. Run the Home Manager installation command and create the first Home
 Manager generation:

home-manager/home-manager

@@ -87,7 +87,7 @@ function setHomeManagerNixPath() {
                 "${XDG_CONFIG_HOME:-$HOME/.config}/nixpkgs/home-manager" \
                 "$HOME/.nixpkgs/home-manager" ; do
         if [[ -e "$path" || "$path" =~ ^https?:// ]] ; then
-            export NIX_PATH="home-manager=$path${NIX_PATH:+:}$NIX_PATH"
+            EXTRA_NIX_PATH+=("home-manager=$path")
             return
         fi
     done
@@ -130,7 +130,6 @@ function doInspectOption() {
         exit 1
     fi
     setConfigFile
-    setHomeManagerNixPath
 
     local extraArgs=("$@")
 
@@ -170,7 +169,6 @@ function doInstantiate() {
         exit 1
     fi
     setConfigFile
-    setHomeManagerNixPath
 
     local extraArgs=()
 
@@ -192,7 +190,6 @@ function doInstantiate() {
 
 function doBuildAttr() {
     setConfigFile
-    setHomeManagerNixPath
 
     local extraArgs=("$@")
 
@@ -602,6 +599,8 @@ COMMAND=""
 COMMAND_ARGS=()
 FLAKE_ARG=""
 
+setHomeManagerNixPath
+
 while [[ $# -gt 0 ]]; do
     opt="$1"
     shift