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Date: Thu, 13 Aug 2026 22:04:22 +0900
Message-Id: <DKNU5IBDCA44.28C93KM4IQS44@nvidia.com>
From: "Alexandre Courbot" <acourbot@nvidia.com>
To: "Younes Akhouayri" <git@younes.io>
Cc: "Rust For Linux" <rust-for-linux@vger.kernel.org>, "Yury Norov"
 <yury.norov@gmail.com>, "Ojeda" <ojeda@kernel.org>, "Yu Whisper Personal"
 <yu.whisper.personal@gmail.com>
Subject: Re: From<bool> and Bounded's invariant for signed N = 1
References: <OzuVxu0--J-9@younes.io>
In-Reply-To: <OzuVxu0--J-9@younes.io>
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On Thu Aug 13, 2026 at 6:46 PM JST, Younes Akhouayri wrote:
> Hi,
>
> There seems to be an invariant violation in the generic From<bool>
> implementation for Bounded.
>
> As I understand it, Bounded<i8, 1> can represent only -1 and 0, while
> i8::from(true) produces 1. However, this safe code is accepted:
>
> let value: Bounded<i8, 1> =3D true.into();
> let _raw: i8 =3D *value;
>
> Bounded::<i8, 1>::try_new(1) rejects the same value, but From<bool>
> passes it directly to the unsafe __new() constructor. The resulting
> Bounded value violates the invariant relied upon by Deref, whose
> failure branch calls unreachable_unchecked().
>
> Am I missing an intended constraint on this conversion? If not, it
> seems the signed N =3D 1 case needs to be excluded or handled
> differently.
>
> Any thoughts?

I think you are correct. There is a `Signedness` associated type on the
`Integer` trait, so it should be trivial to exclude signed integers - do
you want to send a patch for that?