No compiler warning for valueClassInstance == value

[scabug]

When comparing a value class instance with the value itself, I expect a compiler warning the same way as is issued if comparing unrelated objects.

In the example below, the instance of S and 10 are recognized as unrelated (as expected), but the value class instance of T and 10 are not recognized as unrelated (although they are never equal). This is dangerous, since I want to use value classes just for the purpose of having e.g. a type-safe implementation of "Size" that can not be mixed by accident with other Int values. So the compiler should enforce comparing a size like this: "currentFileSize == new Size(10)" (where currentFileSize is an instance of the value type Size). Instead, if I write "currentFileSize == 10", I always get "false" and no warning about it.

scala> class S(val n: Int)
defined class S

scala> val s = new S(10)
s: S = S@56a96eba

scala> s == 10
<console>:10: warning: S and Int are unrelated: they will most likely never compare equal
              s == 10
                ^
res0: Boolean = false

scala> class T(val n: Int) extends AnyVal
defined class T

scala> val t = new T(10)
t: T = T@a

scala> t == 10
res1: Boolean = false

scala>

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6943?orig=1
Reporter: Georg Dietrich (ugdietrich)
Affected Versions: 2.10.0

[scabug]

@paulp said:
scala/scala#2444