feat: emit the old value as second argument in Signals from SignalGro…

…upDescriptor (evented dataclass) (#257)

* add emit_old_value

* style(pre-commit.ci): auto fixes [...]

* merge conflicts

* merge conflicts

* correct tests

* minimal changes

* correct signal signature

* test: fix bench

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Talley Lambert <[email protected]>

src/psygnal/_group_descriptor.py

@@ -155,7 +155,7 @@ def _build_dataclass_signal_group(
         else:
             eq_map[name] = _pick_equality_operator(type_)
         field_type = object if type_ is None else type_
-        signals[name] = sig = Signal(field_type)
+        signals[name] = sig = Signal(field_type, field_type)
         # patch in our custom SignalInstance class with maxargs=1 on connect_setattr
         sig._signal_instance_class = _DataclassFieldSignalInstance
 
@@ -204,7 +204,7 @@ def __enter__(self) -> None:
     def __exit__(self, *args: Any) -> None:
         new: Any = getattr(self.obj, self.field, _NULL)
         if not _check_field_equality(type(self.obj), self.field, self._prev, new):
-            self.signal.emit(new)
+            self.signal.emit(new, self._prev)
 
 
 SetAttr = Callable[[Any, str, Any], None]

tests/test_bench.py

@@ -24,6 +24,7 @@
     "print",
 ]
 
+
 # fmt: off
 class Emitter:
     one_int = Signal(int)
@@ -221,6 +222,9 @@ def _doit() -> None:
         foo.e = (2, "hello")
 
     benchmark(_doit)
-    for newval, attr in zip([2, "hello", False, 2.0, (2, "hello")], "abcde"):
-        mock.assert_any_call(EmissionInfo(getattr(foo.events, attr), (newval,)))
-        assert getattr(foo, attr) == newval
+    for emitted, attr in zip(
+        [(2, 1), ("hello", "hi"), (False, True), (2.0, 1.0), ((2, "hello"), (1, "hi"))],
+        "abcde",
+    ):
+        mock.assert_any_call(EmissionInfo(getattr(foo.events, attr), emitted))
+        assert getattr(foo, attr) == emitted[0]

tests/test_evented_decorator.py

@@ -45,7 +45,7 @@ def _check_events(cls, events_ns="events"):
     assert obj.bar == 1
     obj.bar = 2
     assert obj.bar == 2
-    mock.assert_called_once_with(2)
+    mock.assert_called_once_with(2, 1)
 
     mock.reset_mock()
     obj.baz = "3"

tests/test_group_descriptor.py

@@ -126,7 +126,7 @@ class Foo:
     foo._events.a.connect(mock)
     foo.a = 2
     if patch_setattr:
-        mock.assert_called_once_with(2)
+        mock.assert_called_once_with(2, 1)
     else:
         mock.assert_not_called()
 
@@ -142,7 +142,8 @@ class Foo:
 
         @_group_descriptor.evented_setattr("_events")
         def __setattr__(self, __name: str, __value: Any) -> None:
-            mock1(__name, __value)
+            old = getattr(self, __name, None)
+            mock1(__name, __value, old)
             super().__setattr__(__name, __value)
 
     assert _group_descriptor.is_evented(Foo.__setattr__)
@@ -154,8 +155,8 @@ def __setattr__(self, __name: str, __value: Any) -> None:
     mock = Mock()
     foo._events.a.connect(mock)
     foo.a = 2
-    mock.assert_called_once_with(2)  # confirm no double event emission
-    mock1.assert_called_with("a", 2)
+    mock.assert_called_once_with(2, 1)  # confirm no double event emission
+    mock1.assert_called_with("a", 2, 1)
 
 
 def test_no_getattr_on_non_evented_fields() -> None:
@@ -180,7 +181,7 @@ def b(self, value: int) -> None:
     foo = Foo(a=1)
     foo.events.a.connect(a_mock)
     foo.a = 2
-    a_mock.assert_called_once_with(2)
+    a_mock.assert_called_once_with(2, 1)
 
     foo.b = 1
     b_mock.assert_not_called()  # getter shouldn't have been called