gtk/templates: Add missing traits for TemplateChild

Fixes #1842

gtk4-macros/tests/templates.rs

@@ -303,3 +303,50 @@ glib::wrapper! {
 fn blueprint_file() {
     let _: MyWidget5 = glib::Object::new();
 }
+
+mod imp6 {
+    use super::*;
+
+    #[derive(Default, glib::Properties, gtk::CompositeTemplate)]
+    #[template(string = r#"
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+<template class="TestWidget" parent="GtkWidget">
+<child>
+<object class="GtkWidget" id="widget" />
+</child>
+</template>
+</interface>
+"#)]
+    #[properties(wrapper_type = super::TestWidget)]
+    pub struct TestWidget {
+        #[property(get)]
+        #[template_child]
+        test_widget: gtk::TemplateChild<gtk::Widget>,
+    }
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for TestWidget {
+        const NAME: &'static str = "TestWidget";
+        type Type = super::TestWidget;
+        type ParentType = gtk::Widget;
+
+        fn class_init(klass: &mut Self::Class) {
+            klass.bind_template();
+        }
+
+        fn instance_init(obj: &glib::subclass::InitializingObject<Self>) {
+            obj.init_template();
+        }
+    }
+
+    #[glib::derived_properties]
+    impl ObjectImpl for TestWidget {}
+    impl WidgetImpl for TestWidget {}
+    impl TestWidget {}
+}
+
+glib::wrapper! {
+    pub struct TestWidget(ObjectSubclass<imp6::TestWidget>)
+    @extends gtk::Widget;
+}

gtk4/src/subclass/widget.rs

@@ -1245,6 +1245,43 @@ where
     }
 }
 
+impl<T> ToValue for TemplateChild<T>
+where
+    T: ToValue + ObjectType + FromGlibPtrNone<*mut <T as ObjectType>::GlibType>,
+{
+    #[inline]
+    fn to_value(&self) -> glib::Value {
+        T::to_value(&self.get())
+    }
+
+    #[inline]
+    fn value_type(&self) -> glib::Type {
+        T::static_type()
+    }
+}
+
+impl<T> glib::value::ValueType for TemplateChild<T>
+where
+    T: glib::value::ValueType + ObjectType + FromGlibPtrNone<*mut <T as ObjectType>::GlibType>,
+{
+    type Type = <T as glib::value::ValueType>::Type;
+}
+
+unsafe impl<'a, T> glib::value::FromValue<'a> for TemplateChild<T>
+where
+    T: ObjectType + FromGlibPtrNone<*mut <T as ObjectType>::GlibType>,
+{
+    type Checker = glib::value::GenericValueTypeChecker<T>;
+
+    #[inline]
+    unsafe fn from_value(value: &'a glib::Value) -> Self {
+        skip_assert_initialized!();
+        TemplateChild {
+            ptr: T::from_value(value).as_ptr(),
+        }
+    }
+}
+
 impl<T> std::ops::Deref for TemplateChild<T>
 where
     T: ObjectType + FromGlibPtrNone<*mut <T as ObjectType>::GlibType>,