Re: [PATCH] rust: num: reject bool conversion to signed one-bit Bounded

On Sat Aug 15, 2026 at 9:06 AM BST, Younes Akhouayri via B4 Relay wrote:
> From: Younes Akhouayri <[email protected]>
>
> From<bool> turns true into 1. A signed Bounded with N = 1 can hold
> only -1 and 0. From<bool> therefore creates a value that the type does
> not allow. Deref assumes the value is valid and calls
> unreachable_unchecked() when it is not. Safe Rust can therefore reach
> undefined behavior.
>
> Rust cannot write N >= 2 directly in this From implementation. Add a
> private BoolFits trait. It accepts every valid unsigned width and signed
> widths from 2 through 128. The current Integer types do not use more
> than 128 bits, so this keeps every valid conversion.

Given that the existing `From<Bounded<T, N>> for uXX` implementation all
requires signedness match, I think this is being inconsistent (if we view bool
as u1). I think restricting it to just unsigned integer is better.

Best,
Gary

>
> Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type")
> Closes: https://lore.kernel.org/rust-for-linux/[email protected]/
> Cc: [email protected]
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Younes Akhouayri <[email protected]>