Implement all checks for kinds of type references

[gunnarmorling]

Currently still missing are references in:

• method return values
• (nested) type arguments
• constructor calls
• super-class and implemented interfaces
• annotations
• annotation parameters
• assignments to Class variables (Class<?> cls = InvalidAcess.class)
• unused "named" import (com.foo.bar)
• import "on demand" (com.foo.*)
• usages of qualified Types without importing it (eg private other.Bar bar)
• a static method call on an imported type: Bar.bar() (interestingly it is, if the type is not imported and the invocation is other.Bar.bar())
• accessing static fields (String s = Bar.BAR);
• Class literals: foo(Bar.class);
• Generic bounds: Class<? extends Bar> clazz = null;
• Class literal in annotation: @MyAnno(Bar.class)
• Parameters of lambda expressions: v -> { }
• Local inferred variables: var s = getSomething()

[gunnarmorling]

@nilshartmann FYI, logged this issue for completing the detection logic in the visitor.

[gunnarmorling]

I've already expanded the BasicPluginTest to cover the ones above except the super-type ones (commented out the assertions for now).

[nilshartmann]

ok, I'll merge with my tests and push my work-in-progress state

[gunnarmorling]

Thanks, @nilshartmann!

[gunnarmorling]

@nilshartmann Just noticed some more situation where no error is raised:

• a static method call on an imported type: Bar.bar() (interestingly it is, if the type is not imported and the invocation is other.Bar.bar())
• accessing static fields (String s = Bar.BAR);
• Class literals: foo(Bar.class);
• Generic bounds: Class<? extends Bar> clazz = null;
• Class literal in annotation: @MyAnno(Bar.class)

[nilshartmann]

I'll have a look!

[gunnarmorling]

@nilshartmann, added two more cases to the check list above.

[nilshartmann]

@gunnarmorling , I'll add tests for them. If you don't mind you could merge #25 already. Even the new tests in that PR doesn't cover all cases, they'll provide some more safety.

[gunnarmorling]

If you don't mind you could merge #25 already

We can merge it, but it's still missing license headers in some files. Can you run mvn license:format, update the PR and merge it yourself? Thanks!

[gunnarmorling]

@nilshartmann Added the license headers and merged #25. Thanks!