I'm configuring a new laptop and installed MySQL 8.0.11 "Oracle is Benevolent Edition". This may have been a mistake, but it's a mistake that normal users could easily make.
In the default configuration, I'm getting an error #2054, "The server requested authentication method unknown to the client") when trying to connect. Phabricator doesn't handle this specially so it looks like a generic connection failure. This is misleading because the server is running and, e.g., mysql -uroot ... works fine to connect to it.