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, 2 insertions, 0 deletions

diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index 178fe8e6cb6d..7a90249ee9b9 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -17,6 +17,8 @@ pub use alloc::{boxed::Box, vec::Vec};
 
 pub use macros::{module, vtable};
 
+pub use super::build_assert;
+
 pub use super::{dbg, pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
 
 pub use super::static_assert;