Manual installation of SIL 2.1 on top of SMW 4.0.2 yields UnexpectedValueException in ExtensionRegistry.php

[hhappel]

Setup and configuration

• MW version. 1.37.6
• PHP version: 8.0.25
• SMW version: 4.0.2
• SIL version: 2.1
• DB (MySQL etc. and version): 5.7.40-43-log

Issue

Due to #95 I tried a manual installation of SIL in the same MW instance. Once activated, the Wiki showed the following error message:

Fatal error: Uncaught UnexpectedValueException: callback 'SemanticInterlanguageLinks::initExtension' is not callable in /is/htdocs/REPLACED/hp/w/includes/registration/ExtensionRegistry.php:572 Stack trace: #0 /is/htdocs/REPLACED/hp/w/includes/registration/ExtensionRegistry.php(258): ExtensionRegistry->exportExtractedData(Array) #1 /is/htdocs/REPLACED/hp/w/includes/Setup.php(168): ExtensionRegistry->loadFromQueue() #2 /is/htdocs/REPLACED/hp/w/includes/WebStart.php(90): require_once('/is/htdocs/wp13...') #3 /is/htdocs/REPLACED/hp/w/index.php(44): require('/is/htdocs/wp13...') #4 {main} thrown in /is/htdocs/REPLACED/hp/w/includes/registration/ExtensionRegistry.php on line 572

I found some references for the same/similar exception at

• PHP Fatal error: Uncaught UnexpectedValueException: callback 'SemanticResultFormats::initExtension' is not callable in includes/registration/ExtensionRegistry.php:360 SemanticResultFormats#452
• https://askubuntu.com/questions/1146057/i-get-this-error-when-i-try-to-load-the-maps-extension-how-can-i-fix-it

..which however did not lead anywhere.