Re: [PATCH v3 16/27] rust: types: add `ForLt` trait for higher-ranked lifetime support

[Danilo Krummrich]

On Tue May 19, 2026 at 1:39 PM CEST, Gary Guo wrote:
> Danilo, what do you think?

Two thoughts about this:

  (1) The blast radius is bigger than just auxiliary device registrations; this
      pattern is applicable to all kinds of registrations that provide the
      guarantee to be scoped to the bus device being bound. I.e. it is true for
      any class device registration, IRQ registration, etc. They should all
      support HRT eventually; there is a subsequent series where I started to
      implement this for DRM.

  (2) I'm not concerned about the UnsafeForLtImpl approach, as I think for a
      human one would really need to be willing to abuse it by intention. I.e.
      it is not really different to just using unsafe {} while knowing not to be
      able to satisfy the safety requirement.

      That said, I expect LLMs to be (heavily) used to write drivers, and LLMs
      are typically trained to be compliant. So, I could imagine that a prompt
      along the lines of "Can't we make this work without unsafe somehow?" leads
      to an LLM abusing this, while going unnoticed for the user.

That said, I think that requiring define_for_lt!() wouldn't be that big of an
issue; the number of registrations per driver is rather limited.

Besides that, considering (2) it may actually address a practical concern.

If you want to make the change I'm happy to integrate it in a v4, otherwise a
follow-up seems reasonable as well.