After attempting to update to Magento 2.3.7-p2, a PHP Fatal Error occurs upon reindexing with the following message:
PHP Fatal error: Uncaught Error: Call to undefined method Magento\Framework\Model\ResourceModel\Db\VersionControl\Snapshot::clear() in /var/www/magento/vendor/magento/module-eav/Model/Entity/Collection/VersionControl/AbstractCollection.php:98
This error seems to be related to a call to an undefined method in the VersionControl class during the reindexing process.
Possible Causes
Incompatibility between the Magento version and installed modules
An incomplete or incorrect update process
A conflict with third-party extensions
Solution
1. Check Module Compatibility
Ensure that all installed modules are compatible with Magento 2.3.7-p2.
Incompatibility with the updated Magento version can lead to such fatal errors.
2. Complete Update Process
Revert to the previous version and ensure that the update to 2.3.7-p2 is done correctly.
Incomplete updates can leave the system in an inconsistent state, leading to fatal errors.
3. Disable Third-Party Extensions
Disable all third-party extensions and run the reindex process again.
If the error doesn't occur after disabling the extensions, there might be a conflict with one or more of them.
Re-enable them one by one to identify the problematic extension.
4. Review Custom Code
Review any custom code that interacts with the Entity Collection VersionControl to ensure that it is not causing the error.
It's possible that custom changes are calling the method clear() which is not defined in the Magento core code.
5. Debugging
If the issue persists, debug the reindexing process using tools like Xdebug.
Look into the stack trace to identify the root cause of the error.
Check the files mentioned in the stack trace - AbstractCollection.php and Source.php - to identify any inconsistencies.
By investigating these areas, you can narrow down the cause of the fatal error and take appropriate action to resolve it.