Re: [PATCH v3 03/12] rust: xarray: add `contains_index` method

[Alice Ryhl]

On Thu, Feb 12, 2026 at 11:52 AM Andreas Hindborg <a.hindborg@xxxxxxxxxx> wrote:
>
> Andreas Hindborg <a.hindborg@xxxxxxxxxx> writes:
>
> > As far as I understand, this is a borrow checker limitation. It is easy
> > for us to look at this code and decide that the borrow on line 51 will
> > never alias with the borrow on line 49.
>
> I did a bit of googling, and this seems to be a well known issue with
> the current implementation of lifetime analysis in the rust compiler.
> Apparently this kind of code used to be OK [1] but the Rust devs decided
> to remove the code that allowed this, because it was causing excessive
> compilation times [2]. The upside is that this is solved by the new
> lifetime analysis implementation called "Polonius" and it is the
> intention to replace the existing implementation with Polonius at some
> point [3].

I believe the standard fix for this issue is to provide an entry api
similar to HashMap::entry(). See the rbtree for an example, as it
already provides such API.

Alice