[PATCH 1/2] rust: make unsafe_precondition_assert! const compatible

[JX]

The no-message form of unsafe_precondition_assert! routes the
stringified condition through the formatting machinery. This prevents
the macro from being used in const unsafe functions.

Build its static diagnostic with concat! instead. This preserves the
message while allowing the no-message form in const contexts. Keep the
custom-message form unchanged since it intentionally supports runtime
formatting.

Suggested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Link: https://github.com/Rust-for-Linux/linux/issues/1232
Signed-off-by: JX <1239989762@xxxxxx>
---
 rust/kernel/safety.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/safety.rs b/rust/kernel/safety.rs
index c1c6bd0fa2..a45a574709 100644
--- a/rust/kernel/safety.rs
+++ b/rust/kernel/safety.rs
@@ -7,6 +7,8 @@
 /// The check is enabled at runtime if debug assertions (`CONFIG_RUST_DEBUG_ASSERTIONS`)
 /// are enabled. Otherwise, this macro is a no-op.
 ///
+/// The form without a custom message can be used in const contexts.
+///
 /// # Examples
 ///
 /// ```no_run
@@ -40,7 +42,13 @@
 #[macro_export]
 macro_rules! unsafe_precondition_assert {
     ($cond:expr $(,)?) => {
-        $crate::unsafe_precondition_assert!(@inner $cond, ::core::stringify!($cond))
+        ::core::debug_assert!(
+            $cond,
+            ::core::concat!(
+                "unsafe precondition violated: ",
+                ::core::stringify!($cond),
+            ),
+        )
     };
 
     ($cond:expr, $($arg:tt)+) => {
-- 
2.54.0