rust: qom: add ObjectImpl::CLASS_INIT

As shown in the PL011 device, the orphan rules required a manual
implementation of ClassInitImpl for anything not in the qemu_api crate;
this gets in the way of moving system emulation-specific code (including
DeviceClass, which as a blanket ClassInitImpl<DeviceClass> implementation)
into its own crate.

Make ClassInitImpl optional, at the cost of having to specify the CLASS_INIT
member by hand in every implementation of ObjectImpl.  The next commits will
get rid of it, replacing all the "impl<T> ClassInitImpl<Class> for T" blocks
with a generic class_init<T> method on Class.

Right now the definition is always the same, but do not provide a default
as that will not be true once ClassInitImpl goes away.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/rust/hw/char/pl011/src/device.rs b/rust/hw/char/pl011/src/device.rs
index bea9723..ead361b 100644
--- a/rust/hw/char/pl011/src/device.rs
+++ b/rust/hw/char/pl011/src/device.rs
@@ -160,6 +160,7 @@ impl ObjectImpl for PL011State {
 
     const INSTANCE_INIT: Option<unsafe fn(&mut Self)> = Some(Self::init);
     const INSTANCE_POST_INIT: Option<fn(&Self)> = Some(Self::post_init);
+    const CLASS_INIT: fn(&mut Self::Class) = <Self as ClassInitImpl<Self::Class>>::class_init;
 }
 
 impl DeviceImpl for PL011State {
@@ -744,6 +745,8 @@ unsafe impl ObjectType for PL011Luminary {
 
 impl ObjectImpl for PL011Luminary {
     type ParentType = PL011State;
+
+    const CLASS_INIT: fn(&mut Self::Class) = <Self as ClassInitImpl<Self::Class>>::class_init;
 }
 
 impl DeviceImpl for PL011Luminary {}