rust: build_assert: add `build_{error,assert}!` macros

Add the `build_error!` and `build_assert!` macros which leverage
the previously introduced `build_error` crate. Do so in a new
module, called `build_assert`.

The former fails the build if the code path calling it can possibly
be executed. The latter asserts that a boolean expression is `true`
at compile time.

In particular, `build_assert!` can be used in some contexts where
`static_assert!` cannot:

    fn f1<const N: usize>() {
        static_assert!(N > 1);` // Error.
        build_assert!(N > 1);   // Build-time check.
        assert!(N > 1);         // Run-time check.
    }

    #[inline]
    fn f2(n: usize) {
        static_assert!(n > 1);  // Error.
        build_assert!(n > 1);   // Build-time check.
        assert!(n > 1);         // Run-time check.
    }

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 9b83ef736298..a3abc110ff97 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -23,6 +23,7 @@ compile_error!("Missing kernel configuration for conditional compilation");
 #[cfg(not(test))]
 #[cfg(not(testlib))]
 mod allocator;
+mod build_assert;
 pub mod error;
 pub mod prelude;
 pub mod print;
@@ -35,6 +36,9 @@ pub mod str;
 pub use bindings;
 pub use macros;
 
+#[doc(hidden)]
+pub use build_error::build_error;
+
 /// Prefix to appear before log messages printed from within the `kernel` crate.
 const __LOG_PREFIX: &[u8] = b"rust_kernel\0";