The AL language proactive debugging experience is greatly enhanced by code analyzers. Code analyzers are part of the standard AL Language extension, and are a set of contextual rules that are applied to extension development. These rules can generate an error or a warning when you're developing an extension.
Code analyzers can be enabled and disabled at will, both per workspace and globally.
To enable code analyzers, perform the following steps:
Go to File | Preferences | Settings (Workspace settings) | Extension | AL language extension and choose to edit the settings.json file.