Upstream CI switched to 23.0 by default a month ago: https://github.com/rabbitmq/rabbitmq-server/commit/30d3ffb89a5a27982c45da57f961461cd27cf9a6 Current depends pull in outdated erlang: """ $ emerge -pv1 net-misc/rabbitmq-server These are the packages that would be merged, in order: Calculating dependencies... done! [ebuild N ] dev-python/simplejson-3.17.2::gentoo PYTHON_TARGETS="python3_7 (-pypy3) -python2_7 -python3_6 -python3_8 (-python3_9)" 82 KiB [ebuild UD~] dev-lang/erlang-22.3.4:0/22.3.4::gentoo [23.0.2:0/23.0.2::gentoo] USE="emacs hipe kpoll ssl systemd -doc -java -libressl -odbc -sctp -tk -wxwidgets" 0 KiB [ebuild N ] net-misc/rabbitmq-server-3.8.4::gentoo 3 014 KiB Total: 3 packages (1 downgrade, 2 new), Size of downloads: 3 096 KiB !!! Multiple package instances within a single package slot have been pulled !!! into the dependency graph, resulting in a slot conflict: dev-lang/erlang:0 (dev-lang/erlang-22.3.4:0/22.3.4::gentoo, ebuild scheduled for merge) USE="emacs hipe kpoll ssl systemd -doc -java -libressl -odbc -sctp -tk -wxwidgets" ABI_X86="(64)" pulled in by <dev-lang/erlang-23.0[ssl] required by (net-misc/rabbitmq-server-3.8.4:0/0::gentoo, ebuild scheduled for merge) USE="" ABI_X86="(64)" ^ ^^^^ (dev-lang/erlang-23.0.2:0/23.0.2::gentoo, installed) USE="emacs hipe kpoll ssl systemd -doc -java -libressl -odbc -sctp -tk -wxwidgets" ABI_X86="(64)" pulled in by >=dev-lang/erlang-21:0/23.0.2=[ssl] required by (dev-lang/elixir-1.10.4:0/0::gentoo, installed) USE="test" ABI_X86="(64)" """
rabbitmq-server-3.8.7 seems to allow erlang-23.0 (was added on Sept 2). Filed bug #744568 to stabilize it.