rust: split Rust-only "common" crate

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Link: https://lore.kernel.org/r/20250827104147.717203-6-marcandre.lureau@redhat.com
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 148 insertions, 0 deletions

diff --git a/rust/common/src/assertions.rs b/rust/common/src/assertions.rs
new file mode 100644
index 0000000000..91f83a5d3d
--- /dev/null
+++ b/rust/common/src/assertions.rs
@@ -0,0 +1,148 @@
+// Copyright 2024, Red Hat Inc.
+// Author(s): Paolo Bonzini <pbonzini@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#![doc(hidden)]
+//! This module provides macros to check the equality of types and
+//! the type of `struct` fields.  This can be useful to ensure that
+//! types match the expectations of C code.
+//!
+//! Documentation is hidden because it only exposes macros, which
+//! are exported directly from `common`.
+
+// Based on https://stackoverflow.com/questions/64251852/x/70978292#70978292
+// (stackoverflow answers are released under MIT license).
+
+#[doc(hidden)]
+pub trait EqType {
+    type Itself;
+}
+
+impl<T> EqType for T {
+    type Itself = T;
+}
+
+/// Assert that two types are the same.
+///
+/// # Examples
+///
+/// ```
+/// # use common::assert_same_type;
+/// # use std::ops::Deref;
+/// assert_same_type!(u32, u32);
+/// assert_same_type!(<Box<u32> as Deref>::Target, u32);
+/// ```
+///
+/// Different types will cause a compile failure
+///
+/// ```compile_fail
+/// # use common::assert_same_type;
+/// assert_same_type!(&Box<u32>, &u32);
+/// ```
+#[macro_export]
+macro_rules! assert_same_type {
+    ($t1:ty, $t2:ty) => {
+        const _: () = {
+            #[allow(unused)]
+            fn assert_same_type(v: $t1) {
+                fn types_must_be_equal<T, U>(_: T)
+                where
+                    T: $crate::assertions::EqType<Itself = U>,
+                {
+                }
+                types_must_be_equal::<_, $t2>(v);
+            }
+        };
+    };
+}
+
+/// Assert that a field of a struct has the given type.
+///
+/// # Examples
+///
+/// ```
+/// # use common::assert_field_type;
+/// pub struct A {
+///     field1: u32,
+/// }
+///
+/// assert_field_type!(A, field1, u32);
+/// ```
+///
+/// Different types will cause a compile failure
+///
+/// ```compile_fail
+/// # use common::assert_field_type;
+/// # pub struct A { field1: u32 }
+/// assert_field_type!(A, field1, i32);
+/// ```
+#[macro_export]
+macro_rules! assert_field_type {
+    (@internal $param_name:ident, $ti:ty, $t:ty, $($field:tt)*) => {
+        const _: () = {
+            #[allow(unused)]
+            const fn assert_field_type($param_name: &$t) {
+                const fn types_must_be_equal<T, U>(_: &T)
+                where
+                    T: $crate::assertions::EqType<Itself = U>,
+                {
+                }
+                types_must_be_equal::<_, $ti>(&$($field)*);
+            }
+        };
+    };
+
+    ($t:ty, $i:tt, $ti:ty) => {
+        $crate::assert_field_type!(@internal v, $ti, $t, v.$i);
+    };
+}
+
+/// Assert that an expression matches a pattern.  This can also be
+/// useful to compare enums that do not implement `Eq`.
+///
+/// # Examples
+///
+/// ```
+/// # use common::assert_match;
+/// // JoinHandle does not implement `Eq`, therefore the result
+/// // does not either.
+/// let result: Result<std::thread::JoinHandle<()>, u32> = Err(42);
+/// assert_match!(result, Err(42));
+/// ```
+#[macro_export]
+macro_rules! assert_match {
+    ($a:expr, $b:pat) => {
+        assert!(
+            match $a {
+                $b => true,
+                _ => false,
+            },
+            "{} = {:?} does not match {}",
+            stringify!($a),
+            $a,
+            stringify!($b)
+        );
+    };
+}
+
+/// 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 common::static_assert;
+/// static_assert!("abc".len() == 3);
+/// ```
+///
+/// ```compile_fail
+/// # use common::static_assert;
+/// static_assert!("abc".len() == 2); // does not compile
+/// ```
+#[macro_export]
+macro_rules! static_assert {
+    ($x:expr) => {
+        const _: () = assert!($x);
+    };
+}