error/E0691: include alignment in error message

Include the computed alignment of the violating field when rejecting
transparent types with non-trivially aligned ZSTs.

ZST member fields in transparent types must have an alignment of 1 (to
ensure it does not raise the layout requirements of the transparent
field). The current error message looks like this:

 LL | struct Foobar(u32, [u32; 0]);
    |                    ^^^^^^^^ has alignment larger than 1

This patch changes the report to include the alignment of the violating
field:

 LL | struct Foobar(u32, [u32; 0]);
    |                    ^^^^^^^^ has alignment of 4, which is larger than 1

In case of unknown alignments, it will yield:

 LL | struct Foobar<T>(u32, [T; 0]);
    |                       ^^^^^^ may have alignment larger than 1

This allows developers to get a better grasp why a specific field is
rejected. Knowing the alignment of the violating field makes it easier
to judge where that alignment-requirement originates, and thus hopefully
provide better hints on how to mitigate the problem.

This idea was proposed in 2022 in #98071 as part of a bigger change.
This commit simply extracts this error-message change, to decouple it
from the other diagnostic improvements.

0 files changed, 0 insertions, 0 deletions