If you have a project where you have:

• Rails 4.0 and no easy way of upgrading to Rails 4.2.2
• Ruby 2.0 and no easy way of upgrading to Ruby 2.3 or later
• MySQL database, with mysql2 gem
• MacOS 10.14 or later

Then you are stuck using mysql2 -v 0.3.x branch, which does not natively build anymore. To “fix” this, we have to install MySQL5.7 and point bundler to the mysql config file:

  brew install mysql@5.7
  brew info mysql@5.7 #take note of the install direcotry
  bundle config build.mysql2 --with-mysql-config=/usr/local/Cellar/mysql\@5.7/5.7.24/bin/mysql_config
  bundle install

Now fix that bug and tell your client that we have maintenance to do and upgrade to Rails 4.2.2 or higher and gain a free speed improvement by upgrading to Ruby 2.3.