Many warnings occur!

• lib/cinch/utilities/encoding.rb:20
• lib/cinch/utilities/encoding.rb:33
• lib/cinch/logger.rb:118

I merged cinchrb/cinch#195 into master.
It introduced the quit thread, but the thread uses a busy loop.
The thread should sleep until needed, so it is preferable to use a condition variable.

Cinch::IRC#connect may log the SocketError that occurred on a connection.
In a non-English Windows environment, the message of that exception has the ASCII-8BIT encoding which causes an Encoding::CompatibilityError on encoding it to UTF-8.
I confirmed it on Ubuntu 18.04 running in VirtualBox on a Windows host.

Solution

begin
  # ...
rescue SocketError => e
  e.message.force_encoding(Encoding.default_external)
end

References

• https://tickets.puppetlabs.com/si/jira.issueviews:issue-html/PUP-8368/PUP-8368.html
• https://bugs.ruby-lang.org/issues/14384

A Cinch bot configured to use dummy encoding (e.g. ISO-2022-JP) doesn't work due to Encoding::CompatibilityError. The root cause is that Cinch::Utilities::Encoding.#encode_incoming doesn't encode the given string to UTF-8 (Cinch's internal encoding).

A GUI program using Cinch should show connection established/error messages to the user. But Cinch has no mechanism to notify events about connection. If it exists, it will be useful.

The reference implementation: bcdice/bcdice-irc@cb965a2#diff-a2c0e56343700be5e4608706740d72bd