Re: [linux-next:master 9676/10599] ld.lld: error: undefined symbol: rust_build_error

[Gary Guo <gary@garyguo.net>]

On Fri, 21 Nov 2025 15:21:45 +0100
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:

> On Fri, Nov 21, 2025 at 3:10 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > This kind of thing is why I keep saying build_error() is too fragile to
> > be used at all.  

The case here I think is a perfectly fine use case of `build_error` as
it's completely by-value and does involve references. If compiler can't
figure out, it's either a compiler bug or a source bug.

> Adding `unsafe` blocks for things that should be able to be statically
> known isn't great.
> 
> `build_assert!` is just too useful, so it is best to try to understand
> what can be done, or find an equivalent solution. Gary et al. may have
> some input here.

I'd argue that these build issues actually helps us catch missed
optimisations opportunities :)

For this particular issue, I noticed that none of the functions
involved here (`from_expr` and `fits_within`) are marked as `#[inline]`.
I suspect after marking them as inline this case should be resolved.

Best,
Gary