Missing respond_to_missing? when delegating to Mysql2::Client

[ivoanjo]

Hey 👋!

I'm Ivo and I work at Datadog on our ddtrace gem.

Recently we ran into a bug with the way mysql2-aurora replaces the Mysql2::Client class. When our gem is starting up, it probes which version of libmysqlclient is in use by the mysql2 gem to decide if it should apply a workaround for a bug in old versions of this library.

It did this by checking the following:

defined?(Mysql2::Client) && Mysql2::Client.respond_to?(:info)

libmysqlclient_version = Gem::Version.new(Mysql2::Client.info[:version])

The extra safety checks need to happen because we don't know if mysql2 is installed or correctly loaded.

These checks failed when mysql2-aurora was loaded because it doesn't implement respond_to_missing? on the class that replaces Mysql2::Client. This broke our check and we needed to add a workaround for it (DataDog/dd-trace-rb#2956) as we were getting this output:

irb(main):002:0> Mysql2::Client.respond_to?(:info)
=> false
irb(main):003:0> Mysql2::Client.info[:version]
=> "8.0.33"

In our case, we've added the workaround, but I thought I'd report this issue upstream, so that hopefully this can be fixed and we can in the future remove the workaround :)

Have an awesome week!