glib: Decouple ObjectInterface impl from interface class struct

This makes ObjectInterface and ObjectSubclass more similar to each other
and allows for cleaner separation between unsafe ffi code and application
implementation.

glib-macros/tests/object_subclass_dynamic.rs

@@ -11,13 +11,21 @@ mod static_ {
         // impl for an object interface to register as a static type.
         #[derive(Clone, Copy)]
         #[repr(C)]
-        pub struct MyStaticInterface {
+        pub struct MyStaticInterfaceClass {
             parent: glib::gobject_ffi::GTypeInterface,
         }
 
+        unsafe impl InterfaceClassStruct for MyStaticInterfaceClass {
+            type Type = MyStaticInterface;
+        }
+
+        pub struct MyStaticInterface;
+
         #[glib::object_interface]
-        unsafe impl ObjectInterface for MyStaticInterface {
+        impl ObjectInterface for MyStaticInterface {
             const NAME: &'static str = "MyStaticInterface";
+
+            type Class = MyStaticInterfaceClass;
         }
 
         pub trait MyStaticInterfaceImpl: ObjectImpl + ObjectSubclass {}
@@ -69,15 +77,22 @@ mod module {
         // impl for a object interface to register as a dynamic type and that extends `MyStaticInterface`.
         #[derive(Clone, Copy)]
         #[repr(C)]
-        pub struct MyModuleInterface {
+        pub struct MyModuleInterfaceClass {
             parent: glib::gobject_ffi::GTypeInterface,
         }
 
+        unsafe impl InterfaceClassStruct for MyModuleInterfaceClass {
+            type Type = MyModuleInterface;
+        }
+
+        pub struct MyModuleInterface;
+
         #[glib::object_interface]
         #[object_interface_dynamic]
-        unsafe impl ObjectInterface for MyModuleInterface {
+        impl ObjectInterface for MyModuleInterface {
             const NAME: &'static str = "MyModuleInterface";
             type Prerequisites = (MyStaticInterface,);
+            type Class = MyModuleInterfaceClass;
         }
 
         pub trait MyModuleInterfaceImpl: ObjectImpl + ObjectSubclass {}
@@ -106,15 +121,22 @@ mod module {
         // impl for an object interface to lazy register as a dynamic type and that extends `MyStaticInterface`.
         #[derive(Clone, Copy)]
         #[repr(C)]
-        pub struct MyModuleInterfaceLazy {
+        pub struct MyModuleInterfaceLazyClass {
             parent: glib::gobject_ffi::GTypeInterface,
         }
 
+        unsafe impl InterfaceClassStruct for MyModuleInterfaceLazyClass {
+            type Type = MyModuleInterfaceLazy;
+        }
+
+        pub struct MyModuleInterfaceLazy;
+
         #[glib::object_interface]
         #[object_interface_dynamic(lazy_registration = true)]
-        unsafe impl ObjectInterface for MyModuleInterfaceLazy {
+        impl ObjectInterface for MyModuleInterfaceLazy {
             const NAME: &'static str = "MyModuleInterfaceLazy";
             type Prerequisites = (MyStaticInterface,);
+            type Class = MyModuleInterfaceLazyClass;
         }
 
         pub trait MyModuleInterfaceLazyImpl: ObjectImpl + ObjectSubclass {}
@@ -295,15 +317,22 @@ pub mod plugin {
         // impl for a object interface to register as a dynamic type and that extends `MyStaticInterface`.
         #[derive(Clone, Copy)]
         #[repr(C)]
-        pub struct MyPluginInterface {
+        pub struct MyPluginInterfaceClass {
             parent: glib::gobject_ffi::GTypeInterface,
         }
 
+        unsafe impl InterfaceClassStruct for MyPluginInterfaceClass {
+            type Type = MyPluginInterface;
+        }
+
+        pub struct MyPluginInterface;
+
         #[glib::object_interface]
         #[object_interface_dynamic(plugin_type = super::MyPlugin)]
-        unsafe impl ObjectInterface for MyPluginInterface {
+        impl ObjectInterface for MyPluginInterface {
             const NAME: &'static str = "MyPluginInterface";
             type Prerequisites = (MyStaticInterface,);
+            type Class = MyPluginInterfaceClass;
         }
 
         pub trait MyPluginInterfaceImpl: ObjectImpl + ObjectSubclass {}
@@ -332,15 +361,22 @@ pub mod plugin {
         // impl for an object interface to lazy register as a dynamic type and that extends `MyStaticInterface`.
         #[derive(Clone, Copy)]
         #[repr(C)]
-        pub struct MyPluginInterfaceLazy {
+        pub struct MyPluginInterfaceLazyClass {
             parent: glib::gobject_ffi::GTypeInterface,
         }
 
+        unsafe impl InterfaceClassStruct for MyPluginInterfaceLazyClass {
+            type Type = MyPluginInterfaceLazy;
+        }
+
+        pub struct MyPluginInterfaceLazy;
+
         #[glib::object_interface]
         #[object_interface_dynamic(plugin_type = super::MyPlugin, lazy_registration = true)]
-        unsafe impl ObjectInterface for MyPluginInterfaceLazy {
+        impl ObjectInterface for MyPluginInterfaceLazy {
             const NAME: &'static str = "MyPluginInterfaceLazy";
             type Prerequisites = (MyStaticInterface,);
+            type Class = MyPluginInterfaceLazyClass;
         }
 
         pub trait MyPluginInterfaceLazyImpl: ObjectImpl + ObjectSubclass {}

glib/src/object.rs

@@ -1317,6 +1317,15 @@ macro_rules! glib_object_wrapper {
         );
     };
 
+    (@object_interface [$($attr:meta)*] $visibility:vis $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)?, $iface:ty,
+    @type_ $get_type_expr:expr, @requires [$($requires:tt)*]) => {
+       $crate::glib_object_wrapper!(
+           @interface [$($attr)*] $visibility $name $(<$($generic $(: $bound $(+ $bound2)*)?),+>)?, $iface, std::os::raw::c_void,
+           @ffi_class  <$iface as $crate::subclass::interface::ObjectInterface>::Class,
+           @type_ $get_type_expr, @requires [$($requires)*]
+       );
+   };
+
     (@interface [$($attr:meta)*] $visibility:vis $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)?, $impl_type:ty, $ffi_name:ty, @ffi_class $ffi_class_name:ty,
      @type_ $get_type_expr:expr, @requires [$($requires:tt)*]) => {
         $crate::glib_object_wrapper!(

glib/src/subclass/interface.rs

@@ -2,7 +2,7 @@
 
 use std::{marker, mem};
 
-use super::{InitializingType, Signal};
+use super::{types::InterfaceClassStruct, InitializingType, Signal};
 use crate::{prelude::*, translate::*, Object, ParamSpec, Type, TypeFlags, TypeInfo};
 
 // rustdoc-stripper-ignore-next
@@ -69,17 +69,15 @@ pub unsafe trait ObjectInterfaceType {
 
 /// The central trait for defining a `GObject` interface.
 ///
-/// Links together the type name, and the interface struct for type registration and allows hooking
-/// into various steps of the type registration and initialization.
-///
-/// This must only be implemented on `#[repr(C)]` structs and have `gobject_ffi::GTypeInterface` as
-/// the first field.
+/// Links together the type name, the empty instance and class structs for type
+/// registration and allows hooking into various steps of the type registration
+/// and initialization.
 ///
 /// See [`register_interface`] for registering an implementation of this trait
 /// with the type system.
 ///
 /// [`register_interface`]: fn.register_interface.html
-pub unsafe trait ObjectInterface: ObjectInterfaceType + Sized + 'static {
+pub trait ObjectInterface: ObjectInterfaceType + Sized + 'static {
     /// `GObject` type name.
     ///
     /// This must be unique in the whole process.
@@ -91,6 +89,10 @@ pub unsafe trait ObjectInterface: ObjectInterfaceType + Sized + 'static {
     /// in case of interfaces.
     type Prerequisites: PrerequisiteList;
 
+    // rustdoc-stripper-ignore-next
+    /// The C class struct.
+    type Class: InterfaceClassStruct<Type = Self>;
+
     /// Additional type initialization.
     ///
     /// This is called right after the type was registered and allows
@@ -107,7 +109,7 @@ pub unsafe trait ObjectInterface: ObjectInterfaceType + Sized + 'static {
     /// and for setting default implementations of interface functions.
     ///
     /// Optional
-    fn interface_init(&mut self) {}
+    fn interface_init(_klass: &mut Self::Class) {}
 
     /// Properties installed for this interface.
     ///
@@ -155,12 +157,12 @@ unsafe extern "C" fn interface_init<T: ObjectInterface>(
     klass: ffi::gpointer,
     _klass_data: ffi::gpointer,
 ) {
-    let iface = &mut *(klass as *mut T);
+    let iface = &mut *(klass as *mut T::Class);
 
     let pspecs = <T as ObjectInterface>::properties();
     for pspec in pspecs {
         gobject_ffi::g_object_interface_install_property(
-            iface as *mut T as *mut _,
+            iface as *mut T::Class as *mut _,
             pspec.to_glib_none().0,
         );
     }
@@ -171,10 +173,10 @@ unsafe extern "C" fn interface_init<T: ObjectInterface>(
         signal.register(type_);
     }
 
-    iface.interface_init();
+    T::interface_init(iface);
 }
 
-/// Register a `glib::Type` ID for `T`.
+/// Register a `glib::Type` ID for `T::Class`.
 ///
 /// This must be called only once and will panic on a second call.
 ///
@@ -195,7 +197,7 @@ pub fn register_interface<T: ObjectInterface>() -> Type {
         let type_ = gobject_ffi::g_type_register_static_simple(
             Type::INTERFACE.into_glib(),
             type_name.as_ptr(),
-            mem::size_of::<T>() as u32,
+            mem::size_of::<T::Class>() as u32,
             Some(interface_init::<T>),
             0,
             None,
@@ -216,7 +218,7 @@ pub fn register_interface<T: ObjectInterface>() -> Type {
     }
 }
 
-/// Registers a `glib::Type` ID for `T` as a dynamic type.
+/// Registers a `glib::Type` ID for `T::Class` as a dynamic type.
 ///
 /// An object interface must be explicitly registered as a dynamic type when
 /// the system loads the implementation by calling [`TypePluginImpl::use_`] or
@@ -243,7 +245,7 @@ pub fn register_dynamic_interface<P: DynamicObjectRegisterExt, T: ObjectInterfac
             gobject_ffi::g_type_from_name(type_name.as_ptr()) != gobject_ffi::G_TYPE_INVALID;
 
         let type_info = TypeInfo(gobject_ffi::GTypeInfo {
-            class_size: mem::size_of::<T>() as u16,
+            class_size: mem::size_of::<T::Class>() as u16,
             class_init: Some(interface_init::<T>),
             ..TypeInfo::default().0
         });

glib/src/subclass/mod.rs

@@ -450,9 +450,9 @@ pub mod prelude {
         type_module::{TypeModuleImpl, TypeModuleImplExt},
         type_plugin::{TypePluginImpl, TypePluginImplExt, TypePluginRegisterImpl},
         types::{
-            ClassStruct, InstanceStruct, InstanceStructExt, IsImplementable, IsSubclassable,
-            IsSubclassableExt, ObjectSubclass, ObjectSubclassExt, ObjectSubclassIsExt,
-            ObjectSubclassType,
+            ClassStruct, InstanceStruct, InstanceStructExt, InterfaceClassStruct, IsImplementable,
+            IsSubclassable, IsSubclassableExt, ObjectSubclass, ObjectSubclassExt,
+            ObjectSubclassIsExt, ObjectSubclassType,
         },
     };
 }

glib/src/subclass/object.rs

@@ -460,9 +460,16 @@ mod test {
             parent: gobject_ffi::GTypeInterface,
         }
 
+        unsafe impl InterfaceClassStruct for DummyInterface {
+            type Type = Dummy;
+        }
+
+        pub struct Dummy;
+
         #[glib::object_interface]
-        unsafe impl ObjectInterface for DummyInterface {
+        impl ObjectInterface for Dummy {
             const NAME: &'static str = "Dummy";
+            type Class = DummyInterface;
         }
     }
 
@@ -475,7 +482,7 @@ mod test {
     }
 
     wrapper! {
-        pub struct Dummy(ObjectInterface<imp::DummyInterface>);
+        pub struct Dummy(ObjectInterface<imp::Dummy>);
     }
 
     unsafe impl<T: ObjectSubclass> IsImplementable<T> for Dummy {}

glib/src/subclass/types.rs

@@ -5,7 +5,7 @@
 
 use std::{any::Any, collections::BTreeMap, marker, mem, ptr};
 
-use super::SignalId;
+use super::{interface::ObjectInterface, SignalId};
 use crate::{
     object::{IsClass, IsInterface, ObjectSubclassIs, ParentClassIs},
     prelude::*,
@@ -280,11 +280,29 @@ impl<U: IsClass + ParentClassIs> IsSubclassableExt for U {
 }
 
 // rustdoc-stripper-ignore-next
-/// Trait for implementable interfaces.
-pub unsafe trait IsImplementable<T: ObjectSubclass>: IsInterface
+/// Trait implemented by structs that implement a `GTypeInterface` C class struct.
+///
+/// This must only be implemented on `#[repr(C)]` structs and have
+/// `gobject_ffi::GTypeInterface` as the first field.
+pub unsafe trait InterfaceClassStruct: Sized + 'static
 where
-    <Self as ObjectType>::GlibClassType: Copy,
+    Self: Copy,
 {
+    // rustdoc-stripper-ignore-next
+    /// Corresponding object interface type for this class struct.
+    type Type: ObjectInterface;
+
+    // rustdoc-stripper-ignore-next
+    /// Set up default implementations for interface vfuncs.
+    ///
+    /// This is automatically called during type initialization.
+    #[inline]
+    fn interface_init(&mut self) {}
+}
+
+// rustdoc-stripper-ignore-next
+/// Trait for implementable interfaces.
+pub unsafe trait IsImplementable<T: ObjectSubclass>: IsInterface {
     // rustdoc-stripper-ignore-next
     /// Override the virtual methods of this interface for the given subclass and do other
     /// interface initialization.
@@ -305,22 +323,22 @@ unsafe extern "C" fn interface_init<T: ObjectSubclass, A: IsImplementable<T>>(
 ) where
     <A as ObjectType>::GlibClassType: Copy,
 {
-    let iface = &mut *(iface as *mut crate::Interface<A>);
+    let klass = &mut *(iface as *mut crate::Interface<A>);
 
     let mut data = T::type_data();
     if data.as_ref().parent_ifaces.is_none() {
         data.as_mut().parent_ifaces = Some(BTreeMap::default());
     }
     {
-        let copy = Box::new(*iface.as_ref());
+        let copy = Box::new(*klass.as_ref());
         data.as_mut()
             .parent_ifaces
             .as_mut()
             .unwrap()
             .insert(A::static_type(), Box::into_raw(copy) as ffi::gpointer);
     }
 
-    A::interface_init(iface);
+    A::interface_init(klass);
 }
 
 // rustdoc-stripper-ignore-next
@@ -631,7 +649,7 @@ pub trait ObjectSubclass: ObjectSubclassType + Sized + 'static {
     // rustdoc-stripper-ignore-next
     /// The C class struct.
     ///
-    /// See [`basic::ClassStruct`] for an basic instance struct that should be
+    /// See [`basic::ClassStruct`] for an basic class struct that should be
     /// used in most cases.
     ///
     /// [`basic::ClassStruct`]: ../basic/struct.ClassStruct.html

glib/src/wrapper.rs

@@ -436,8 +436,7 @@ macro_rules! wrapper {
         $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (ObjectInterface<$iface_name:ty>) $(@requires $($requires:path),+)?;
     ) => {
         $crate::glib_object_wrapper!(
-            @interface [$($attr)*] $visibility $name $(<$($generic $(: $bound $(+ $bound2)*)?),+>)?, *mut std::os::raw::c_void, std::os::raw::c_void,
-            @ffi_class $iface_name,
+            @object_interface [$($attr)*] $visibility $name $(<$($generic $(: $bound $(+ $bound2)*)?),+>)?, $iface_name,
             @type_ $crate::translate::IntoGlib::into_glib(<$iface_name as $crate::subclass::interface::ObjectInterfaceType>::type_()),
             @requires [$( $($requires),+ )?]
         );