Date: Thu, 13 Aug 2026 11:46:32 +0200 (CEST)
From: Younes Akhouayri <git@younes.io>
To: Rust For Linux <rust-for-linux@vger.kernel.org>
Cc: Acourbot <acourbot@nvidia.com>, Yury Norov <yury.norov@gmail.com>,
	Ojeda <ojeda@kernel.org>,
	Yu Whisper Personal <yu.whisper.personal@gmail.com>,
	Git <git@younes.io>
Message-ID: <OzuVxu0--J-9@younes.io>
Subject: From<bool> and Bounded's invariant for signed N = 1
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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> = true.into();
let _raw: i8 = *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 = 1 case needs to be excluded or handled
differently.

Any thoughts?

Thanks,
Younes