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/qemu-api/tests/tests.rs b/rust/qemu-api/tests/tests.rs
index 03569e4..9546e9d 100644
--- a/rust/qemu-api/tests/tests.rs
+++ b/rust/qemu-api/tests/tests.rs
@@ -60,6 +60,7 @@ unsafe impl ObjectType for DummyState {
 impl ObjectImpl for DummyState {
     type ParentType = DeviceState;
     const ABSTRACT: bool = false;
+    const CLASS_INIT: fn(&mut DummyClass) = <Self as ClassInitImpl<DummyClass>>::class_init;
 }
 
 impl ResettablePhasesImpl for DummyState {}
@@ -102,6 +103,8 @@ unsafe impl ObjectType for DummyChildState {
 impl ObjectImpl for DummyChildState {
     type ParentType = DummyState;
     const ABSTRACT: bool = false;
+    const CLASS_INIT: fn(&mut DummyChildClass) =
+        <Self as ClassInitImpl<DummyChildClass>>::class_init;
 }
 
 impl ResettablePhasesImpl for DummyChildState {}