Yeah this is a bit stupid from the ruby side, see below...

> root@fireball / # emerge -auDN world
> 
> These are the packages that would be merged, in order:
> 
> Calculating dependencies |
> 
> !!! Problem resolving dependencies for sci-electronics/klayout from
> @selected
> ... done!
> Dependency resolution took 4.79 s.
> 
> 
> !!! The ebuild selected to satisfy "sci-electronics/klayout" has unmet
> requirements.
> - sci-electronics/klayout-0.28.5::gentoo USE="" ABI_X86="(64)"
> PYTHON_SINGLE_TARGET="python3_11 -python3_10" RUBY_TARGETS="-ruby30"
> 
>   The following REQUIRED_USE flag constraints are unsatisfied:
>     ruby_targets_ruby30
> 
>   The above constraints are a subset of the following complete expression:
>     exactly-one-of ( python_single_target_python3_10
> python_single_target_python3_11 ) any-of ( ruby_targets_ruby30 )

^ Essentially, it wants "ruby_targets_ruby30" to be enabled, but the default
switched to 3.1.  
The ruby eclass misses the feature of the python eclasses that you can build
against "one of the following"...

As you already noticed, 0.28.9 wants "ruby_targets_ruby31" and is thus fine
with the new default. 
(And it's also stable since now.)



-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, toolchain, base-system, perl, libreoffice)