Re: [PATCH v7 05/10] rust: bitmap: add contiguous area operations

[Alexandre Courbot]

On Fri Aug 21, 2026 at 5:31 PM JST, Miguel Ojeda wrote:
> On Fri, Aug 21, 2026 at 10:11 AM Alexandre Courbot <acourbot@xxxxxxxxxx> wrote:
>>
>> Mutating methods should definitely keep that check, but for querying
>> this looks like a legitimate way to use the API.
>
> If there is a need to use the API in a certain way (and there is no
> other intended/"better" way to do something), then yeah.
>
> Otherwise, having `debug_assert!`s or similar are more than welcome.

I think there are two kinds of operations to distinguish here:

- Setting/clearing a bit, which can be thought of as an array access
  operation. These are accepted to panic in Rust, so it makes sense that
  the bitmap methods do the same. There is a side-effect expected, if it
  cannot be performed then something has to report it.
- Look for a bit/group of bits that match a certain condition. These
  operations don't have any side-effect, so IMHO it is fine to say that
  there are no bits set after `start` if `start >= self.len()`.

I'm not super fond of the different behavior introduced by
CONFIG_RUST_BITMAP_HARDENED. We don't have a fallback in Rust to
silently not set an array element if its index is invalid - we only have
panicking and checked variants. Bitmaps should not be different. Fixing
this (if that's desired) is beyond this patchset, but maybe we can at
least make the `next*` operations avoid that.