Use same args signatures for PO#on_signal and POI#on_signal

Fixes issue mvidner#31;
ProxyObjectInterface#on_signal shares now the arguments signature whit
ProxyObject#on_signal and can be used without specifying explicitly the
bus parameter, since the POI itself already owns the reference of the
bus is being used on.

Author: stoffie

lib/dbus/introspect.rb

@@ -299,9 +299,24 @@ def define_method(methodname, prototype)
       define(m)
     end
 
+    # @overload on_signal(name, &block)
+    # @overload on_signal(bus, name, &block)
     # Registers a handler (code block) for a signal with _name_ arriving
     # over the given _bus_. If no block is given, the signal is unregistered.
-    def on_signal(bus, name, &block)
+    # Note that specifying _bus_ is discouraged and the option is kept only for
+    # backward compatibility.
+    def on_signal(*args, &block)
+      # Since we must function under ruby 1.8.7, it isn't possible to define the
+      # function as on_signal(bus = nil, name, &block)
+      bus = case args.size
+              when 1
+                @object.bus
+              when 2
+                args.shift
+              else
+                raise ArgumentError, "wrong number of arguments (#{args.size} for 1-2)"
+            end
+      name = args.shift
       mr = DBus::MatchRule.new.from_signal(self, name)
       if block.nil?
         bus.remove_match(mr)
@@ -435,7 +450,7 @@ def has_iface?(name)
     # It uses _default_iface_ which must have been set.
     def on_signal(name, &block)
       if @default_iface and has_iface?(@default_iface)
-        @interfaces[@default_iface].on_signal(@bus, name, &block)
+        @interfaces[@default_iface].on_signal(name, &block)
       else
         # TODO improve
         raise NoMethodError

test/signal_test.rb

@@ -10,13 +10,15 @@ def setup
     @obj = svc.object("/org/ruby/MyInstance")
     @obj.introspect                  # necessary
     @obj.default_iface = "org.ruby.Loop"
+    @intf = @obj["org.ruby.Loop"]
 
     @loop = DBus::Main.new
     @loop << @session_bus
   end
 
   # testing for commit 017c83 (kkaempf)
   def test_overriding_a_handler
+    DBus.logger.debug "Inside test_overriding_a_handler"
     counter = 0
 
     @obj.on_signal "LongTaskEnd" do
@@ -47,6 +49,31 @@ def test_overriding_a_handler
     assert_equal 1, counter
   end
 
+  def test_on_signal_backward_compatibility
+    DBus.logger.debug "Inside test_on_signal_backward_compatibility"
+    counter = 0
+    # Same as intf.on_signal("LongTaskEnd"), just the old way
+    @intf.on_signal @obj.bus, "LongTaskEnd" do
+      counter += 1
+    end
+    @obj.LongTaskBegin 3
+    quitter = Thread.new do
+      DBus.logger.debug "sleep before quit"
+      sleep 1
+      DBus.logger.debug "will quit"
+      @loop.quit
+    end
+    @loop.run
+    quitter.join
+
+    assert_equal 1, counter
+  end
+
+  def test_on_signal_args_check
+    assert_raise(ArgumentError) {@intf.on_signal } # not enough
+    assert_raise(ArgumentError) {@intf.on_signal 'to', 'many', 'yarrrrr!'}
+  end
+
   def test_too_many_rules
     100.times do
       @obj.on_signal "Whichever" do