Re: [PATCH v8 03/12] rust: num: add cv! macro to create values from constant expressions

[Alice Ryhl <aliceryhl@google.com>]

On Thu, Aug 27, 2026 at 04:28:31PM +0900, Eliot Courtney wrote:
> Currently, using NonZero/Bounded constants is quite verbose. It's
> unfortunate because it disincentivizes using it in interface boundaries.
> Introduce a macro to make it nicer to use. The macro `cv!` (for constant
> value) takes a const integer expression and widens it to i128 (at build
> time only) before passing it as a const generic value to a new trait
> function `FromConst::from_const`. The trait is implemented by NonZero,
> Bounded, and Alignment and lets values of each be constructed from
> constants without a verbose turbofish syntax. For example,
> `const { NonZero::new(1).unwrap() }` can be written as `cv!(1)`.
> 
> Suggested-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>

This doesn't work in const context, so I don't think this is a great
strategy.

I would want to use it for cases like this:

drivers/android/binder/netlink.rs
        const BINDER_CMD_REPORT: u8 = kernel::uapi::BINDER_CMD_REPORT as u8;
        const BINDER_A_REPORT_ERROR: c_int = kernel::uapi::BINDER_A_REPORT_ERROR as c_int;
        const BINDER_A_REPORT_CONTEXT: c_int = kernel::uapi::BINDER_A_REPORT_CONTEXT as c_int;
        const BINDER_A_REPORT_FROM_PID: c_int = kernel::uapi::BINDER_A_REPORT_FROM_PID as c_int;
        const BINDER_A_REPORT_FROM_TID: c_int = kernel::uapi::BINDER_A_REPORT_FROM_TID as c_int;
        const BINDER_A_REPORT_TO_PID: c_int = kernel::uapi::BINDER_A_REPORT_TO_PID as c_int;
        const BINDER_A_REPORT_TO_TID: c_int = kernel::uapi::BINDER_A_REPORT_TO_TID as c_int;
        const BINDER_A_REPORT_IS_REPLY: c_int = kernel::uapi::BINDER_A_REPORT_IS_REPLY as c_int;
        const BINDER_A_REPORT_FLAGS: c_int = kernel::uapi::BINDER_A_REPORT_FLAGS as c_int;
        const BINDER_A_REPORT_CODE: c_int = kernel::uapi::BINDER_A_REPORT_CODE as c_int;
        const BINDER_A_REPORT_DATA_SIZE: c_int = kernel::uapi::BINDER_A_REPORT_DATA_SIZE as c_int;

Alice