Why doesn't the warning appear in PHP 5.5.9?
git checkout 1e43177
./demo
PHP Warning: Declaration of SpeakCommand::execute() should be compatible with Symfony\Component\Console\Command\Command::execute(Symfony\Component\Console\Input\InputInterface $input, Symfony\Component\Console\Output\OutputInterface $output) in /home/xenial/symcon/src/SpeakCommand.php on line 21
Warning shows up just fine with PHP 7.0.8-0ubuntu0.16.04.2 (cli) ( NTS )