subclassing: move parent invocation fnct in Ext trait

This reduces the risk for the user to override them, or even worse,
let the user believe that it has an actual effect to override them.

See https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/merge_requests/223#note_112472

Author: fengalin

src/subclass/mod.rs

@@ -186,7 +186,7 @@ pub mod prelude {
     //! Prelude that re-exports all important traits from this crate.
     pub use super::boxed::BoxedType;
     pub use super::interface::{ObjectInterface, ObjectInterfaceExt};
-    pub use super::object::{ObjectClassSubclassExt, ObjectImpl};
+    pub use super::object::{ObjectClassSubclassExt, ObjectImpl, ObjectImplExt};
     pub use super::types::{
         ClassStruct, InstanceStruct, IsImplementable, IsSubclassable, ObjectSubclass,
     };

src/subclass/object.rs

@@ -34,7 +34,7 @@ macro_rules! glib_object_impl {
 /// Trait for implementors of `glib::Object` subclasses.
 ///
 /// This allows overriding the virtual methods of `glib::Object`.
-pub trait ObjectImpl: 'static {
+pub trait ObjectImpl: ObjectImplExt + 'static {
     /// Storage for the type-specific data used during registration.
     ///
     /// This is usually generated by the [`glib_object_impl!`] macro.
@@ -66,20 +66,6 @@ pub trait ObjectImpl: 'static {
     fn constructed(&self, obj: &Object) {
         self.parent_constructed(obj);
     }
-
-    /// Chain up to the parent class' implementation of `glib::Object::constructed()`.
-    ///
-    /// Do not override this, it has no effect.
-    fn parent_constructed(&self, obj: &Object) {
-        unsafe {
-            let data = self.get_type_data();
-            let parent_class = data.as_ref().get_parent_class() as *mut gobject_ffi::GObjectClass;
-
-            if let Some(ref func) = (*parent_class).constructed {
-                func(obj.to_glib_none().0);
-            }
-        }
-    }
 }
 
 unsafe extern "C" fn get_property<T: ObjectSubclass>(
@@ -320,7 +306,29 @@ unsafe impl<T: ObjectSubclass> IsSubclassable<T> for ObjectClass {
     }
 }
 
-pub trait ObjectImplExt: ObjectImpl + ObjectSubclass {
+pub trait ObjectImplExt {
+    /// Chain up to the parent class' implementation of `glib::Object::constructed()`.
+    fn parent_constructed(&self, obj: &Object);
+
+    fn signal_chain_from_overridden(
+        &self,
+        token: &super::SignalClassHandlerToken,
+        values: &[Value],
+    ) -> Option<Value>;
+}
+
+impl<T: ObjectImpl + ObjectSubclass> ObjectImplExt for T {
+    fn parent_constructed(&self, obj: &Object) {
+        unsafe {
+            let data = self.get_type_data();
+            let parent_class = data.as_ref().get_parent_class() as *mut gobject_ffi::GObjectClass;
+
+            if let Some(ref func) = (*parent_class).constructed {
+                func(obj.to_glib_none().0);
+            }
+        }
+    }
+
     fn signal_chain_from_overridden(
         &self,
         token: &super::SignalClassHandlerToken,
@@ -336,8 +344,6 @@ pub trait ObjectImplExt: ObjectImpl + ObjectSubclass {
     }
 }
 
-impl<T: ObjectImpl + ObjectSubclass> ObjectImplExt for T {}
-
 #[cfg(test)]
 mod test {
     use super::super::super::object::ObjectExt;