support signatures in dbus_property decorator

The builtin @decorator property recreates itself when the .setter,
.getter or .deleter child-decorators are used. This meant that the
introspection meant for the getter was also being applied to the setter.
I added a guard for this situation to exit early, and instead copy the
already introspected properties over from the getter.

Author: Anders Hellerup Madsen

dbus_next/service.py

@@ -228,18 +228,26 @@ def set_options(self, options):
         self.__dict__['__DBUS_PROPERTY'] = True
 
     def __init__(self, fn, *args, **kwargs):
+        if args:
+            # this is a call to prop.setter - all we need to do call super
+            return super().__init__(fn, *args, **kwargs)
+
         self.prop_getter = fn
         self.prop_setter = None
 
         inspection = inspect.signature(fn)
+
         if len(inspection.parameters) != 1:
             raise ValueError('the property must only have the "self" input parameter')
 
-        return_annotation = parse_annotation(inspection.return_annotation)
+        return_annotation = kwargs.pop('signature', None)
+        if return_annotation is None:
+            return_annotation = parse_annotation(inspection.return_annotation)
 
         if not return_annotation:
             raise ValueError(
-                'the property must specify the dbus type string as a return annotation string')
+                'the property must specify the dbus type string as a return annotation string or with the signature option'
+            )
 
         self.signature = return_annotation
         tree = SignatureTree._get(return_annotation)
@@ -249,26 +257,40 @@ def __init__(self, fn, *args, **kwargs):
 
         self.type = tree.types[0]
 
-        if 'options' in kwargs:
-            options = kwargs['options']
+        options = kwargs.pop('options', None)
+        if options is not None:
             self.set_options(options)
-            del kwargs['options']
 
         super().__init__(fn, *args, **kwargs)
 
     def setter(self, fn, **kwargs):
         # XXX The setter decorator seems to be recreating the class in the list
         # of class members and clobbering the options so we need to reset them.
         # Why does it do that?
+        #
+        #     The default implementation of setter basically looks like this:
+        #
+        #           def setter(self, fset):
+        #               return type(self)(self.fget, fset, self.fdel)
+        #
+        #     That is it creates a new instance, with the new setter, carrying
+        #     the getter and deleter over from the the existing instance.
+        #
+        #     In this case, we need to carry all the private properties from the
+        #     old instance and reset the options on the new instance.
         result = super().setter(fn, **kwargs)
+        result.prop_getter = self.prop_getter
         result.prop_setter = fn
+        result.signature = self.signature
+        result.type = self.type
         result.set_options(self.options)
         return result
 
 
 def dbus_property(access: PropertyAccess = PropertyAccess.READWRITE,
                   name: str = None,
-                  disabled: bool = False):
+                  disabled: bool = False,
+                  signature: Optional[str] = None):
     """A decorator to mark a class method of a :class:`ServiceInterface` to be a DBus property.
 
     The class method must be a Python getter method with a return annotation
@@ -316,7 +338,7 @@ def string_prop(self, val: 's'):
     @no_type_check_decorator
     def decorator(fn):
         options = {'name': name, 'access': access, 'disabled': disabled}
-        return _Property(fn, options=options)
+        return _Property(fn, options=options, signature=signature)
 
     return decorator
 

test/service/test_decorators.py

@@ -10,6 +10,7 @@ def __init__(self):
         self._some_prop = 55
         self._another_prop = 101
         self._weird_prop = 500
+        self._foo_prop = 17
 
     @method()
     def some_method(self, one: 's', two: 's') -> 's':
@@ -19,10 +20,6 @@ def some_method(self, one: 's', two: 's') -> 's':
     def another_method(self, eight: 'o', six: 't'):
         pass
 
-    @method(in_signature="sasu", out_signature="i")
-    def a_third_method(self, one: str, two: List[str], three) -> int:
-        return 42
-
     @signal()
     def some_signal(self) -> 'as':
         return ['result']
@@ -53,6 +50,18 @@ def weird_prop(self) -> 't':
     def setter_for_weird_prop(self, val: 't'):
         self._weird_prop = val
 
+    @method(in_signature="sasu", out_signature="i")
+    def a_third_method(self, one: str, two: List[str], three) -> int:
+        return 42
+
+    @dbus_property(signature='u')
+    def foo_prop(self) -> int:
+        return self._foo_prop
+
+    @foo_prop.setter
+    def foo_prop(self, val: int):
+        self._foo_prop = val
+
 
 def test_method_decorator():
     interface = ExampleInterface()
@@ -101,7 +110,7 @@ def test_method_decorator():
     assert not signal.disabled
     assert type(signal.introspection) is intr.Signal
 
-    assert len(properties) == 3
+    assert len(properties) == 4
 
     renamed_readonly_prop = properties[0]
     assert renamed_readonly_prop.name == 'renamed_readonly_property'
@@ -110,7 +119,18 @@ def test_method_decorator():
     assert renamed_readonly_prop.disabled
     assert type(renamed_readonly_prop.introspection) is intr.Property
 
-    weird_prop = properties[1]
+    foo_prop = properties[1]
+    assert foo_prop.name == 'foo_prop'
+    assert foo_prop.access == PropertyAccess.READWRITE
+    assert foo_prop.signature == 'u'
+    assert not foo_prop.disabled
+    assert foo_prop.prop_getter is not None
+    assert foo_prop.prop_getter.__name__ == 'foo_prop'
+    assert foo_prop.prop_setter is not None
+    assert foo_prop.prop_setter.__name__ == 'foo_prop'
+    assert type(foo_prop.introspection) is intr.Property
+
+    weird_prop = properties[2]
     assert weird_prop.name == 'weird_prop'
     assert weird_prop.access == PropertyAccess.READWRITE
     assert weird_prop.signature == 't'
@@ -121,7 +141,7 @@ def test_method_decorator():
     assert weird_prop.prop_setter.__name__ == 'setter_for_weird_prop'
     assert type(weird_prop.introspection) is intr.Property
 
-    prop = properties[2]
+    prop = properties[3]
     assert prop.name == 'some_prop'
     assert prop.access == PropertyAccess.READWRITE
     assert prop.signature == 'u'
@@ -157,7 +177,7 @@ def test_interface_introspection():
     signals = xml.findall('signal')
     properties = xml.findall('property')
 
-    assert len(xml) == 5
+    assert len(xml) == 6
     assert len(methods) == 2
     assert len(signals) == 1
-    assert len(properties) == 2
+    assert len(properties) == 3