rust: enable clippy::ptr_cast_constness

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/devel/rust.rst

@@ -74,8 +74,6 @@ Supported tools
 QEMU supports rustc version 1.63.0 and newer.  Notably, the following features
 are missing:
 
-* ``cast_mut()``/``cast_const()`` (1.65.0).  Use ``as`` instead.
-
 * Generic Associated Types (1.65.0)
 
 * ``CStr::from_bytes_with_nul()`` as a ``const`` function (1.72.0).

rust/Cargo.toml

@@ -71,6 +71,7 @@ no_effect_underscore_binding = "deny"
 option_option = "deny"
 or_fun_call = "deny"
 ptr_as_ptr = "deny"
+ptr_cast_constness = "deny"
 pub_underscore_fields = "deny"
 redundant_clone = "deny"
 redundant_closure_for_method_calls = "deny"
@@ -92,7 +93,6 @@ used_underscore_binding = "deny"
 
 # nice to have, but cannot be enabled yet
 #wildcard_imports = "deny"   # still have many bindings::* imports
-#ptr_cast_constness = "deny" # needs 1.65.0 for cast_mut()/cast_const()
 
 # these may have false positives
 #option_if_let_else = "deny"

rust/hw/timer/hpet/src/hpet.rs

@@ -219,7 +219,7 @@ impl HPETTimer {
             // SAFETY: the HPETTimer will only be used after the timer
             // is initialized below.
             qemu_timer: unsafe { Timer::new() },
-            state: NonNull::new(state as *const _ as *mut _).unwrap(),
+            state: NonNull::new((state as *const HPETState).cast_mut()).unwrap(),
             config: 0,
             cmp: 0,
             fsb: 0,

rust/qemu-api/src/cell.rs

@@ -1016,7 +1016,7 @@ impl<T> Opaque<T> {
 
     /// Returns a raw pointer to the opaque data.
     pub const fn as_ptr(&self) -> *const T {
-        self.as_mut_ptr() as *const _
+        self.as_mut_ptr().cast_const()
     }
 
     /// Returns a raw pointer to the opaque data that can be passed to a

rust/qemu-api/src/chardev.rs

@@ -160,7 +160,7 @@ impl CharBackend {
                 receive_cb,
                 event_cb,
                 None,
-                (owner as *const T as *mut T).cast::<c_void>(),
+                (owner as *const T).cast_mut().cast::<c_void>(),
                 core::ptr::null_mut(),
                 true,
             );

rust/qemu-api/src/qom.rs

@@ -388,7 +388,7 @@ where
     {
         #[allow(clippy::as_ptr_cast_mut)]
         {
-            self.as_ptr::<U>() as *mut _
+            self.as_ptr::<U>().cast_mut()
         }
     }
 }
@@ -638,7 +638,7 @@ impl<T: ObjectType> Owned<T> {
         // SAFETY NOTE: while NonNull requires a mutable pointer, only
         // Deref is implemented so the pointer passed to from_raw
         // remains const
-        Owned(NonNull::new(ptr as *mut T).unwrap())
+        Owned(NonNull::new(ptr.cast_mut()).unwrap())
     }
 
     /// Obtain a raw C pointer from a reference.  `src` is consumed

rust/qemu-api/src/timer.rs

@@ -81,7 +81,7 @@ impl Timer {
                 scale as c_int,
                 attributes as c_int,
                 Some(timer_cb),
-                (opaque as *const T).cast::<c_void>() as *mut c_void,
+                (opaque as *const T).cast::<c_void>().cast_mut(),
             )
         }
     }