darwin: add --check flag

modules/system/activation-checks.nix

@@ -67,8 +67,15 @@ in
 
     system.activationScripts.checks.text = ''
       set +e
+
       ${buildUsers}
       ${nixPath}
+
+      if test ''${checkActivation:-0} -eq 1; then
+        echo "ok" >&2
+        exit 0
+      fi
+
       set -e
     '';
 

pkgs/nix-tools/darwin-rebuild.sh

@@ -52,6 +52,10 @@ while [ "$#" -gt 0 ]; do
       k="$1"; shift 1
       extraBuildFlags+=("$i" "$j" "$k")
       ;;
+    --check)
+      action="check"
+      export checkActivation=1
+      ;;
     --rollback)
       action="rollback"
       extraProfileFlags=("$i")
@@ -85,12 +89,12 @@ done
 
 if [ -z "$action" ]; then showSyntax; fi
 
-if [ "$action" = switch ]; then
+if [ "$action" = switch -o "$action" = check ]; then
   extraBuildFlags+=("--no-out-link")
 fi
 
 echo "building the system configuration..." >&2
-if [ "$action" = switch -o "$action" = build ]; then
+if [ "$action" = switch -o "$action" = build -o "$action" = check ]; then
   systemConfig="$(nix-build '<darwin>' ${extraBuildFlags[@]} -A system)"
 fi
 
@@ -127,3 +131,7 @@ if [ "$action" = switch -o "$action" = rollback ]; then
     $systemConfig/activate
   fi
 fi
+
+if [ "$action" = check ]; then
+  $systemConfig/activate-user
+fi