rust: num: add cv! macro to create values from constant expressions

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
`FromConst`. The value is then converted and appears in the
associated constant `FromConst::VALUE`. 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)`.

Add the `cv!` macro to the prelude so it doesn't need to be imported
explicitly to use it.

Suggested-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20261013-cv-v5-1-113a538dfaef@nvidia.com
[ Added a few intra-doc links. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

0 files changed, 0 insertions, 0 deletions