Alternative solution for issue 536.
Gives warning "$this might not be bound by invoker of callable or might be bound to object of any class. Consider adding instance class check." for $this var usage.
And hints developer to check class of $this before usage.
Class check can be added in form "if ($this instanceof [class])" {/*use $this*/}.
Note: if class check added no type checking is done its in language server it just hides the warning.
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