Validate that destination, role, and service are not set as labels on roles and accessories

lib/kamal/configuration/validator.rb

@@ -169,6 +169,16 @@ class Kamal::Configuration::Validator
       unknown_keys_error unknown_keys if unknown_keys.present?
     end
 
+    def validate_labels!(labels)
+      with_context("labels") do
+        labels.each do |key, _|
+          with_context(key) do
+            error "invalid label. destination, role, and service are reserved labels" if %w[destination role service].include?(key)
+          end
+        end
+      end
+    end
+
     def validate_docker_options!(options)
       if options
         error "Cannot set restart policy in docker options, unless-stopped is required" if options["restart"]

lib/kamal/configuration/validator/accessory.rb

@@ -6,6 +6,8 @@ class Kamal::Configuration::Validator::Accessory < Kamal::Configuration::Validat
       error "specify one of `host`, `hosts`, `role`, `roles`, `tag` or `tags`"
     end
 
+    validate_labels!(config["labels"]) if config.key?("labels")
+
     validate_docker_options!(config["options"])
   end
 end

lib/kamal/configuration/validator/role.rb

@@ -2,6 +2,8 @@ class Kamal::Configuration::Validator::Role < Kamal::Configuration::Validator
   def validate!
     validate_type! config, Array, Hash
 
+    validate_labels!(config["labels"]) if config.key?("labels")
+
     if config.is_a?(Array)
       validate_servers!(config)
     else