They were stabilized in Rust 1.79.0.
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250908105005.2119297-6-pbonzini@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
docs/devel/rust.rst | 9 +++------
rust/qemu-api/src/callbacks.rs | 27 +--------------------------
rust/qemu-api/src/chardev.rs | 2 +-
rust/qemu-api/src/qdev.rs | 2 +-
rust/qemu-api/src/timer.rs | 2 +-
rust/qemu-api/src/vmstate.rs | 2 +-
6 files changed, 8 insertions(+), 36 deletions(-)
diff --git a/docs/devel/rust.rst b/docs/devel/rust.rst
index e0ee4a9837d..98e3a33a3ce 100644
--- a/docs/devel/rust.rst
+++ b/docs/devel/rust.rst
@@ -79,9 +79,6 @@ QEMU supports rustc version 1.83.0 and newer. The following features
from relatively new versions of Rust are not used for historical reasons;
patches are welcome:
-* inline const expression (stable in 1.79.0), currently worked around with
- associated constants in the ``FnCall`` trait.
-
* associated constants are still explicitly marked ``'static`` (`changed in
1.81.0`__)
@@ -97,9 +94,9 @@ patches are welcome:
before QEMU can use them. For now, there is special code in
``util/error.c`` to support non-NUL-terminated file names.
-* associated const equality would be nice to have for some users of
- ``callbacks::FnCall``, but is still experimental. ``ASSERT_IS_SOME``
- replaces it.
+Associated const equality would be nice to have for some users of
+``callbacks::FnCall``, but is still experimental. Const assertions
+are used instead.
__ https://github.com/rust-lang/rust/pull/125258
diff --git a/rust/qemu-api/src/callbacks.rs b/rust/qemu-api/src/callbacks.rs
index 9642a16eb89..dbe2305f509 100644
--- a/rust/qemu-api/src/callbacks.rs
+++ b/rust/qemu-api/src/callbacks.rs
@@ -113,31 +113,6 @@
/// This is always true for zero-capture closures and function pointers, as long
/// as the code is able to name the function in the first place.
pub unsafe trait FnCall<Args, R = ()>: 'static + Sync + Sized {
- /// Referring to this internal constant asserts that the `Self` type is
- /// zero-sized. Can be replaced by an inline const expression in
- /// Rust 1.79.0+.
- const ASSERT_ZERO_SIZED: () = { assert!(mem::size_of::<Self>() == 0) };
-
- /// Referring to this constant asserts that the `Self` type is an actual
- /// function type, which can be used to catch incorrect use of `()`
- /// at compile time.
- ///
- /// # Examples
- ///
- /// ```compile_fail
- /// # use qemu_api::callbacks::FnCall;
- /// fn call_it<F: for<'a> FnCall<(&'a str,), String>>(_f: &F, s: &str) -> String {
- /// let _: () = F::ASSERT_IS_SOME;
- /// F::call((s,))
- /// }
- ///
- /// let s: String = call_it((), "hello world"); // does not compile
- /// ```
- ///
- /// Note that this can be more simply `const { assert!(F::IS_SOME) }` in
- /// Rust 1.79.0 or newer.
- const ASSERT_IS_SOME: () = { assert!(Self::IS_SOME) };
-
/// `true` if `Self` is an actual function type and not `()`.
///
/// # Examples
@@ -195,7 +170,7 @@ unsafe impl<F, $($args,)* R> FnCall<($($args,)*), R> for F
#[inline(always)]
fn call(a: ($($args,)*)) -> R {
- let _: () = Self::ASSERT_ZERO_SIZED;
+ const { assert!(mem::size_of::<Self>() == 0) };
// SAFETY: the safety of this method is the condition for implementing
// `FnCall`. As to the `NonNull` idiom to create a zero-sized type,
diff --git a/rust/qemu-api/src/chardev.rs b/rust/qemu-api/src/chardev.rs
index 6e0590d758e..cb27be52569 100644
--- a/rust/qemu-api/src/chardev.rs
+++ b/rust/qemu-api/src/chardev.rs
@@ -138,7 +138,7 @@ pub fn enable_handlers<
F::call((owner, event))
}
- let _: () = CanReceiveFn::ASSERT_IS_SOME;
+ const { assert!(CanReceiveFn::IS_SOME) };
let receive_cb: Option<unsafe extern "C" fn(*mut c_void, *const u8, c_int)> =
if ReceiveFn::is_some() {
Some(rust_receive_cb::<T, ReceiveFn>)
diff --git a/rust/qemu-api/src/qdev.rs b/rust/qemu-api/src/qdev.rs
index 36f02fb57db..52d54a4494e 100644
--- a/rust/qemu-api/src/qdev.rs
+++ b/rust/qemu-api/src/qdev.rs
@@ -373,7 +373,7 @@ fn do_init_gpio_in(
}
}
- let _: () = F::ASSERT_IS_SOME;
+ const { assert!(F::IS_SOME) };
unsafe extern "C" fn rust_irq_handler<T, F: for<'a> FnCall<(&'a T, u32, u32)>>(
opaque: *mut c_void,
line: c_int,
diff --git a/rust/qemu-api/src/timer.rs b/rust/qemu-api/src/timer.rs
index 0daec62f926..1e639eaf221 100644
--- a/rust/qemu-api/src/timer.rs
+++ b/rust/qemu-api/src/timer.rs
@@ -56,7 +56,7 @@ pub fn init_full<'timer, 'opaque: 'timer, T, F>(
) where
F: for<'a> FnCall<(&'a T,)>,
{
- let _: () = F::ASSERT_IS_SOME;
+ const { assert!(F::IS_SOME) };
/// timer expiration callback
unsafe extern "C" fn rust_timer_handler<T, F: for<'a> FnCall<(&'a T,)>>(
diff --git a/rust/qemu-api/src/vmstate.rs b/rust/qemu-api/src/vmstate.rs
index 812f390d780..8515e382135 100644
--- a/rust/qemu-api/src/vmstate.rs
+++ b/rust/qemu-api/src/vmstate.rs
@@ -457,7 +457,7 @@ macro_rules! vmstate_exist_fn {
const fn test_cb_builder__<T, F: for<'a> $crate::callbacks::FnCall<(&'a T, u8), bool>>(
_phantom: ::core::marker::PhantomData<F>,
) -> $crate::vmstate::VMSFieldExistCb {
- let _: () = F::ASSERT_IS_SOME;
+ const { assert!(F::IS_SOME) };
$crate::vmstate::rust_vms_test_field_exists::<T, F>
}
--
2.51.0