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

[Andreas Hindborg]

"Alice Ryhl" <aliceryhl@xxxxxxxxxx> writes:

> 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.

The example above [1] is using the BTreeMap entry API to produce the
issue. Are the BTreeMap and HashMap entry APIs significantly different,
or is there something else I missed?

Best regards,
Andreas Hindborg

[1] https://lore.kernel.org/r/87y0kytggx.fsf@xxxxxxxxxx