#1377 Add rule for comparing unrelated types

[Sodiaan]

FindBugs could have a rule to detect the comparing unrelated types in Scala.

:::scala

val a : String = "s"

val b : Int = 42

if (a != b) println("bug")

[Tagir Valeev]

FindBugs is Java static analyzer, not Scala analyzer. Though you can feed FindBugs with scalac-generated bytecode, you will get the enormous number of false-positives and simply irrelevant reports, which makes it practically useless. Thus we are not going to fix something for the Scala code.

In Java the equivalent code produces a compilation error, thus no need to check it with FindBugs:

String a = "s";
Integer b = 42;
if(a != b) // error: incomparable types: String and Integer
    System.out.println("bug");

If you use equals instead of !=, then FindBugs warns:

Call to String.equals(Integer) in test.Unrelated.main(String[])

Also FindBugs warns when you use the Object type:

Object a = "s";
Object b = 42;
if(a != b)
    System.out.println("bug");

FindBugs warning:

Using pointer equality to compare a Integer with a String in test.Unrelated.main(String[])

So everything already works for Java and there's nothing to fix.