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    SubjectRe: [PATCH v1 25/28] rust: add `build_error` crate
    On Thu, Nov 10, 2022 at 05:41:37PM +0100, Miguel Ojeda wrote:
    > From: Gary Guo <gary@garyguo.net>
    [...]
    > diff --git a/rust/build_error.rs b/rust/build_error.rs
    > new file mode 100644
    > index 000000000000..0ff6b33059aa
    > --- /dev/null
    > +++ b/rust/build_error.rs
    > @@ -0,0 +1,24 @@
    > +// SPDX-License-Identifier: GPL-2.0
    > +
    > +//! Build-time error.
    > +//!
    > +//! This crate provides a function `build_error`, which will panic in

    a const function `build_error`

    Without this I read it as a "normal non-const function".

    > +//! compile-time if executed in const context, and will cause a build error
    > +//! if not executed at compile time and the optimizer does not optimise away the
    > +//! call.
    > +//!

    I can work out what the code does, but I also happen to know what Rust's
    const means and its behaviour in non-const context. Other kernel
    developers may not. Even so the description is a bit difficult for me to
    parse.

    Maybe a few sentences about const and its behaviours can help?

    Thanks,
    Wei.

    > +//! It is used by `build_assert!` in the kernel crate, allowing checking of
    > +//! conditions that could be checked statically, but could not be enforced in
    > +//! Rust yet (e.g. perform some checks in const functions, but those
    > +//! functions could still be called in the runtime).
    > +
    > +#![no_std]
    > +
    > +/// Panics if executed in const context, or triggers a build error if not.
    > +#[inline(never)]
    > +#[cold]
    > +#[export_name = "rust_build_error"]
    > +#[track_caller]
    > +pub const fn build_error(msg: &'static str) -> ! {
    > + panic!("{}", msg);
    > +}

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