Consider feature for #[may_dangle] on Drop impl to allow usage in cases where normal Vec works

[laundmo]

Normal Vec uses the unstable #[may_dangle] on its Drop impl, avoiding issues with lifetimes when a ArryaVec is used as a struct field and stores references to other fields of the struct. Smallvec has a feature flag to opt in to doing the same.

Playground with the problem: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=1ae3af28bff1fe47748f747755f47326
change ArrayVec to Vec to see that it works.

references/docs:
https://doc.rust-lang.org/nomicon/dropck.html#an-escape-hatch
https://std-dev-guide.rust-lang.org/tricky/may-dangle.html

[bluss]

Playground link is not the right one.

Unstable code is possible, but unlikely due to maintainability

[laundmo]

fixed the link. I came across this limitation trying to optimize something using https://doc.rust-lang.org/stable/nightly-rustc/rustc_data_structures/sso/map/enum.SsoHashMap.html but running into spooky lifetime issues at a distance due to SsoHashMap being based on arrayvec.

from my understanding, may_dangle has been that way for relatively long and is unlikely to change, plus behind a feature flag it would only be the separate Drop impl.