Magento should create a log entry if an observer does not implement ObserverInterface

[bnymn]

Summary (*)

In developer mode, if an observer does not implement ObserverInterface, Magento throws an exception. This is the expected behavior.

What I don't understand is that it does not do anything for other deploy modes (default and production). It silently discards the observer without even putting an entry to logs.

Examples (*)

This is the method where problem occurs. There is only one condition for developer mode, but other deploy modes are ignored.

    /**
     * @param \Magento\Framework\Event\ObserverInterface $object
     * @param Observer $observer
     * @return $this
     * @throws \LogicException
     */
    protected function _callObserverMethod($object, $observer)
    {
        if ($object instanceof \Magento\Framework\Event\ObserverInterface) {
            $object->execute($observer);
        } elseif ($this->_appState->getMode() == \Magento\Framework\App\State::MODE_DEVELOPER) {
            throw new \LogicException(
                sprintf(
                    'Observer "%s" must implement interface "%s"',
                    get_class($object),
                    \Magento\Framework\Event\ObserverInterface::class
                )
            );
        }
        return $this;
    }

Proposed solution

We can put an else condition. Then, we can log the same exception message in warning level.

[magento-engcom-team]

Hi @bnymn. Thank you for your report.
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@bnymn do you confirm that you was able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
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[magento-engcom-team]

✅ Confirmed by @engcom-backlog-nazar
Thank you for verifying the issue. Based on the provided information internal tickets MAGETWO-98704 were created

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