Hi Alistair,

On Fri, Feb 21, 2025 at 2:20 AM Alistair Popple [off-list ref] wrote:

Is this a known issue or limitation? Or is this a bug/rough edge that still
needs fixing? Or alternatively am I just doing something wrong? Would appreciate
any insights as figuring out what I'd done wrong here was a bit of a rough
introduction!

Yeah, it is a result of our `build_assert!` machinery:

    https://rust.docs.kernel.org/kernel/macro.build_assert.html

which works by producing a build (link) error rather than the usual
compiler error and thus the bad error message.

`build_assert!` is really the biggest hammer we have to assert
something is true at build time, since it may rely on the optimizer.
For instance, if `static_assert!` is usable in that context, it should
be instead of `build_assert!`.

Ideally we would have a way to get the message propagated somehow,
because it is indeed confusing.

I hope that helps.

Cheers,
Miguel