gtk: add Scrollable subclassing support

gtk4/src/subclass/mod.rs

@@ -16,6 +16,7 @@ pub mod layout_manager;
 pub mod list_box_row;
 pub mod native_dialog;
 pub mod popover;
+pub mod scrollable;
 pub mod sorter;
 pub mod style_context;
 pub mod toggle_button;
@@ -37,6 +38,7 @@ pub mod prelude {
     pub use super::list_box_row::ListBoxRowImpl;
     pub use super::native_dialog::NativeDialogImpl;
     pub use super::popover::PopoverImpl;
+    pub use super::scrollable::ScrollableImpl;
     pub use super::sorter::SorterImpl;
     pub use super::style_context::StyleContextImpl;
     pub use super::toggle_button::ToggleButtonImpl;

gtk4/src/subclass/scrollable.rs

@@ -0,0 +1,37 @@
+use crate::{Border, Scrollable};
+use glib::subclass::prelude::*;
+use glib::translate::*;
+use glib::Cast;
+
+pub trait ScrollableImpl: ObjectImpl {
+    fn get_border(&self, scrollable: &Self::Type) -> Option<Border>;
+}
+
+unsafe impl<T: ScrollableImpl> IsImplementable<T> for Scrollable {
+    unsafe extern "C" fn interface_init(
+        iface: glib::ffi::gpointer,
+        _iface_data: glib::ffi::gpointer,
+    ) {
+        let scrollable_iface = &mut *(iface as *mut ffi::GtkScrollableInterface);
+
+        scrollable_iface.get_border = Some(scrollable_get_border::<T>);
+    }
+}
+
+unsafe extern "C" fn scrollable_get_border<T: ScrollableImpl>(
+    scrollable: *mut ffi::GtkScrollable,
+    borderptr: *mut ffi::GtkBorder,
+) -> glib::ffi::gboolean {
+    let instance = &*(scrollable as *mut T::Instance);
+    let imp = instance.get_impl();
+
+    if let Some(border) =
+        imp.get_border(from_glib_borrow::<_, Scrollable>(scrollable).unsafe_cast_ref())
+    {
+        *borderptr = *border.to_glib_full();
+        true.to_glib()
+    } else {
+        *borderptr = *std::ptr::null();
+        false.to_glib()
+    }
+}