Overlay: Add discarding for Java classes, interfaces & fields

Author: kaspersv

java/ql/lib/semmle/code/java/Member.qll

@@ -848,6 +848,9 @@ class Field extends Member, ExprParent, @field, Variable {
   override string getAPrimaryQlClass() { result = "Field" }
 }
 
+overlay[local]
+private class DiscardableField extends DiscardableReferableLocatable, @field { }
+
 /** An instance field. */
 class InstanceField extends Field {
   InstanceField() { not this.isStatic() }

java/ql/lib/semmle/code/java/Type.qll

@@ -16,6 +16,8 @@ import Member
 import Modifier
 import JDK
 
+private import semmle.code.java.Overlay
+
 /**
  * Holds if reference type `t` is an immediate super-type of `sub`.
  */
@@ -998,6 +1000,9 @@ class ClassOrInterface extends RefType, @classorinterface {
   CompanionObject getCompanionObject() { type_companion_object(this, _, result) }
 }
 
+overlay[local]
+private class DiscardableClassOrInterface extends DiscardableReferableLocatable, @classorinterface { }
+
 private string getAPublicObjectMethodSignature() {
   exists(Method m |
     m.getDeclaringType() instanceof TypeObject and