Extensions can't declare constructorsDRT-W1346

The analyzer produces this diagnostic when a constructor declaration is found in an extension. It isn't valid to define a constructor because extensions aren't classes, and it isn't possible to create an instance of an extension.

Example

The following code produces this diagnostic because there is a constructor declaration in E:

extension E on String {
  E() : super();
}

Common fixes

Remove the constructor or replace it with a static method.