Revert "nix: make channel entries for NIX_PATH dynamic"

This reverts commit 95fb1cb2aa, 1324ccf2c1 and e5c988edf1.

CHANGELOG

@@ -1,10 +1,3 @@
-2018-10-26
-- the nix.nixPath option no longer includes the paths for channels, these are
-  added dynamically instead to avoid warnings.  This can be disabled using the
-  following option.
-
-    nix.enableChannels = false;
-
 2018-03-29
 - default nix.package no longer uses the default profile.
   system.stateVersion > 2

modules/nix/default.nix

@@ -315,23 +315,13 @@ in
       default =
         [ # Include default path <darwin-config>.
           "darwin-config=${config.environment.darwinConfig}"
+          "/nix/var/nix/profiles/per-user/root/channels"
+          "$HOME/.nix-defexpr/channels"
         ];
       description = ''
         The default Nix expression search path, used by the Nix
         evaluator to look up paths enclosed in angle brackets
-        (e.g. <literal>&lt;nixpkgs&gt;</literal>).  This value gets
+        (e.g. <literal>&lt;nixpkgs&gt;</literal>).
-        extended with user and/or root channels if those exist and
-        nix.enableChannels isn't disabled.
-      '';
-    };
-
-    nix.enableChannels = mkOption {
-      type = types.bool;
-      default = true;
-      description = ''
-        Whether to extend <envar>NIX_PATH</envar> with <filename>~/.nix-defexpr/channels</filename>
-        and <filename>/nix/var/nix/profiles/per-user/root/channels</filename>
-        if they exist.
       '';
     };
   };
@@ -404,14 +394,6 @@ in
       if [ ! -w /nix/var/nix/db ]; then
           export NIX_REMOTE=daemon
       fi
-    '' + optionalString cfg.enableChannels ''
-      # Set up NIX_PATH with root and/or user channels.
-      if [ -d "$HOME/.nix-defexpr/channels" ]; then
-          export NIX_PATH="''${NIX_PATH:+$NIX_PATH:}$HOME/.nix-defexpr/channels"
-      fi
-      if [ -d /nix/var/nix/profiles/per-user/root/channels ]; then
-          export NIX_PATH="''${NIX_PATH:+$NIX_PATH:}/nix/var/nix/profiles/per-user/root/channels"
-      fi
     '';
 
     # Set up the environment variables for running Nix.

modules/system/checks.nix

@@ -81,7 +81,7 @@ let
   '';
 
   nixPath = ''
-    darwinConfig=$(NIX_PATH="${concatStringsSep ":" config.nix.nixPath}${optionalString config.nix.enableChannels ":$HOME/.nix-defexpr/channels:/nix/var/nix/profiles/per-user/root/channels"}" nix-instantiate --eval -E '<darwin-config>' || echo "$HOME/.nixpkgs/darwin-configuration.nix") || true
+    darwinConfig=$(NIX_PATH=${concatStringsSep ":" config.nix.nixPath} nix-instantiate --eval -E '<darwin-config>' || echo "$HOME/.nixpkgs/darwin-configuration.nix") || true
     if ! test -e "$darwinConfig"; then
         echo "error: Changed <darwin-config> but target does not exist, aborting activation" >&2
         echo "Create $darwinConfig or set environment.darwinConfig:" >&2
@@ -95,7 +95,7 @@ let
         exit 2
     fi
 
-    darwinPath=$(NIX_PATH="${concatStringsSep ":" config.nix.nixPath}${optionalString config.nix.enableChannels ":$HOME/.nix-defexpr/channels:/nix/var/nix/profiles/per-user/root/channels"}" nix-instantiate --eval -E '<darwin>') || true
+    darwinPath=$(NIX_PATH=${concatStringsSep ":" config.nix.nixPath} nix-instantiate --eval -E '<darwin>') || true
     if ! test -e "$darwinPath"; then
         echo "error: Changed <darwin> but target does not exist, aborting activation" >&2
         echo "Add the darwin repo as a channel or set nix.nixPath:" >&2
@@ -109,7 +109,7 @@ let
         exit 2
     fi
 
-    nixpkgsPath=$(NIX_PATH="${concatStringsSep ":" config.nix.nixPath}${optionalString config.nix.enableChannels ":$HOME/.nix-defexpr/channels:/nix/var/nix/profiles/per-user/root/channels"}" nix-instantiate --eval -E '<nixpkgs>') || true
+    nixpkgsPath=$(NIX_PATH=${concatStringsSep ":" config.nix.nixPath} nix-instantiate --eval -E '<nixpkgs>') || true
     if ! test -e "$nixpkgsPath"; then
         echo "error: Changed <nixpkgs> but target does not exist, aborting activation" >&2
         echo "Add a nixpkgs channel or set nix.nixPath:" >&2