[PATCH 1/3] rust: assertions: add static_assert

[Peter Maydell <peter.maydell@linaro.org>]

From: Paolo Bonzini <pbonzini@redhat.com>

Add a new assertion that is similar to "const { assert!(...) }" but can be used
outside functions and with older versions of Rust.  A similar macro is found in
Linux, whereas the "static_assertions" crate has a const_assert macro that
produces worse error messages.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Supersedes: <20250320113356.799412-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 rust/qemu-api/src/assertions.rs | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/rust/qemu-api/src/assertions.rs b/rust/qemu-api/src/assertions.rs
index 104dec39774..bba38cfda11 100644
--- a/rust/qemu-api/src/assertions.rs
+++ b/rust/qemu-api/src/assertions.rs
@@ -120,3 +120,25 @@ macro_rules! assert_match {
         );
     };
 }
+
+/// Assert at compile time that an expression is true.  This is similar
+/// to `const { assert!(...); }` but it works outside functions, as well as
+/// on versions of Rust before 1.79.
+///
+/// # Examples
+///
+/// ```
+/// # use qemu_api::static_assert;
+/// static_assert!("abc".len() == 3);
+/// ```
+///
+/// ```compile_fail
+/// # use qemu_api::static_assert;
+/// static_assert!("abc".len() == 2); // does not compile
+/// ```
+#[macro_export]
+macro_rules! static_assert {
+    ($x:expr) => {
+        const _: () = assert!($x);
+    };
+}
-- 
2.43.0