Which fails due to Racc:
https://copr.fedorainfracloud.org/coprs/pvalena/rubygems-testing/build/48...
The issue seems to be fixed upstream:
https://github.com/ruby/racc/pull/191
It is unfortunate that such a minor bug might influence quite lot of the ecosystem.
Hopefully we will be in better shape in few months. And if on, just remember we have to
fix this one ;)
I've backported this.