Missing hashCode definitions

[fpoli]

The Scalastyle linter complains about missing hashCode definitions in Silver. I'm not sure if we did that intentionally but it seems worth double-checking, adding a comment to Silver if there is nothing to fix.

Defining either equals() or hashCode() in a class without defining the other is a known source of bugs. Usually, when you define one, you should also define the other.

Further Reading: Scalastyle - EqualsHashCode

silver/src/main/scala/viper/silver/ast/utility/rewriter/Strategy.scala

Lines 38 to 44 in c352aa5

	case class NodeEq(node: Rewritable) {
	override def equals(that: Any): Boolean = that match {
	case req: NodeEq => this.node eq req.node
	case ref: AnyRef => this.node eq ref
	case _ => false
	}
	}

silver/src/main/scala/viper/silver/utility/Common.scala

Lines 25 to 37 in c352aa5

	trait StructuralEquality { self: AnyRef =>
	protected val equalityDefiningMembers: Seq[Any]
	override val hashCode = generateHashCode(equalityDefiningMembers)
	override def equals(other: Any) = (
	this.eq(other.asInstanceOf[AnyRef])
	|| (other match {
	case se: StructuralEquality if this.getClass.eq(se.getClass) =>
	equalityDefiningMembers == se.equalityDefiningMembers
	case _ => false
	}))
	}