SystemService#start_modes returns known modes when service is not found

* It does not have enough information to infer which are the supported
  modes.
* This feature is used during first stage.

library/systemd/src/lib/yast2/system_service.rb

@@ -173,6 +173,13 @@ def initialize(service)
       @errors = {}
     end
 
+    # Determines whether the service exists in the underlying system
+    #
+    # @return [Boolean] true if it exists; false otherwise.
+    def found?
+      !service.not_found?
+    end
+
     # State of the service
     #
     # In case the service is not active but socket is, the socket state is considered
@@ -228,8 +235,13 @@ def currently_active?
     # * :on_demand: The service will be started on demand.
     # * :manual:    The service is disabled and it will be started manually.
     #
+    # @note When the service does not exist in the underlying system (for instance,
+    # during 1st stage) all possible start modes are returned, as there is no way
+    # to find out which of them are supported.
+    #
     # @return [Array<Symbol>] List of supported modes.
     def start_modes
+      @start_modes = [:on_boot, :manual, :on_demand] unless found?
       return @start_modes if @start_modes
       @start_modes = [:on_boot, :manual]
       @start_modes << :on_demand if socket

library/systemd/src/lib/yast2/systemd_unit.rb

@@ -81,7 +81,8 @@ class PropMap < Hash
       :loaded?,
       :active_state,
       :sub_state,
-      :can_reload?
+      :can_reload?,
+      :not_found?
     ].freeze
 
     private_constant :FORWARDED_METHODS

library/systemd/test/yast2/system_service_test.rb

@@ -28,14 +28,16 @@
 
   let(:service) do
     instance_double(Yast::SystemdServiceClass::Service,
-      name:     "cups",
-      enabled?: service_enabled,
-      active?:  service_active,
-      refresh!: true)
+      name:       "cups",
+      enabled?:   service_enabled,
+      active?:    service_active,
+      not_found?: !service_found,
+      refresh!:   true)
   end
 
   let(:service_enabled) { true }
   let(:service_active) { true }
+  let(:service_found) { true }
 
   let(:service_socket) do
     instance_double(Yast::SystemdSocketClass::Socket,
@@ -311,6 +313,15 @@
         expect(system_service.start_modes).to contain_exactly(:on_boot, :manual)
       end
     end
+
+    context "when the service is not found" do
+      let(:socket) { nil }
+      let(:service_found) { false }
+
+      it "returns all available start modes" do
+        expect(system_service.start_modes).to contain_exactly(:on_boot, :manual, :on_demand)
+      end
+    end
   end
 
   describe "#start_mode" do
@@ -1093,4 +1104,22 @@
       end
     end
   end
+
+  describe "#found" do
+    context "when the service is found" do
+      let(:service_found) { true }
+
+      it "returns true" do
+        expect(system_service.found?).to eq(true)
+      end
+    end
+
+    context "when the service is not found" do
+      let(:service_found) { false }
+
+      it "returns false" do
+        expect(system_service.found?).to eq(false)
+      end
+    end
+  end
 end