darwin: show CHANGELOG during activation

CHANGELOG

@@ -0,0 +1,16 @@
+2017-07-23
+- darwin entry in default the nix.nixPath was removed
+
+    Use a channel for nix-darwin or configure nix.nixPath
+
+    sudo nix-channel --add https://github.com/LnL7/nix-darwin/archive/master.tar.gz darwin
+    sudo nix-channel --update
+
+    nix.nixPath =
+      [ "darwin=$HOME/.nix-defexpr/darwin"
+        "darwin-config=$HOME/.nixpkgs/darwin-configuration.nix"
+        "/nix/var/nix/profiles/per-user/root/channels"
+      ];
+
+2017-01-09
+- nix.profile was renamed to nix.package

modules/system/activation-checks.nix

@@ -3,6 +3,19 @@
 with lib;
 
 let
+  darwinChanges = ''
+    if test -e /run/current-system/darwin-changes; then
+      darwinChanges=$(grep -v -f /run/current-system/darwin-changes $systemConfig/darwin-changes 2> /dev/null)
+      if test -n "$darwinChanges"; then
+        echo >&2
+        echo "CHANGELOG" >&2
+        echo >&2
+        echo "$darwinChanges" >&2
+        echo >&2
+      fi
+    fi
+  '';
+
   buildUsers = optionalString config.services.nix-daemon.enable ''
     buildUser=$(dscl . -read /Groups/nixbld GroupMembership 2>&1 | awk '/^GroupMembership: / {print $2}')
     if [ -z $buildUser ]; then
@@ -18,7 +31,7 @@ let
     fi
   '';
 
-  nixPath = optionalString true ''
+  nixPath = ''
     darwinConfig=$(NIX_PATH=${concatStringsSep ":" config.nix.nixPath} nix-instantiate --eval -E '<darwin-config>')
     if ! test -e "$darwinConfig"; then
         echo "error: Changed <darwin-config> but target does not exist, aborting activation" >&2
@@ -68,6 +81,7 @@ in
     system.activationScripts.checks.text = ''
       set +e
 
+      ${darwinChanges}
       ${buildUsers}
       ${nixPath}
 

modules/system/default.nix

@@ -87,6 +87,9 @@ in
 
         systemConfig=$out
 
+        mkdir -p $out/darwin
+        cp -f ${<darwin/CHANGELOG>} $out/darwin-changes
+
         ln -s ${cfg.build.etc}/etc $out/etc
         ln -s ${cfg.path} $out/sw