Made synthetic classes extending java.lang.Object. Fix lightbend-labs#74

All classes extends `java.lang.Object`, synthetic (i.e., compiler generated)
classes being no exception.

Furthermore, implemented typesafe equality (`===`) for comparing `ClassInfo`
instances, since the existing calls to `==` where only comparing references
(since `ClassInfo` does not implement `equals`).

core/src/main/scala/com/typesafe/tools/mima/core/ClassInfo.scala

@@ -10,6 +10,13 @@ object ClassInfo {
    *  class path.
    */
   lazy val ObjectClass = Config.baseDefinitions.fromName("java.lang.Object")
+
+  implicit class EqualClassInfo(c1: ClassInfo) {
+    def ===(c2: ClassInfo): Boolean = {
+      if(c1 == null & c2 == null) true
+      else c1 != null && c2 != null && c1.fullName == c2.fullName
+    }
+  }
 }
 
 import com.typesafe.tools.mima.core.util.log.{ConsoleLogging, Logging}
@@ -20,9 +27,9 @@ import com.typesafe.tools.mima.core.util.log.{ConsoleLogging, Logging}
 class SyntheticClassInfo(owner: PackageInfo, override val bytecodeName: String) extends ClassInfo(owner) {
   loaded = true
   def file: AbstractFile = throw new UnsupportedOperationException
-  override lazy val superClasses = Nil
   override lazy val allTraits = Set.empty[ClassInfo]
   override lazy val allInterfaces: Set[ClassInfo] = Set.empty[ClassInfo]
+  override lazy val superClasses = Set(ClassInfo.ObjectClass)
 }
 
 /** As the name implies. */
@@ -97,8 +104,8 @@ abstract class ClassInfo(val owner: PackageInfo) extends HasDeclarationName with
   def flags_=(x: Int) = _flags = x
   def isScala_=(x: Boolean) = _isScala = x
 
-  lazy val superClasses: List[ClassInfo] =
-    (if (this == ClassInfo.ObjectClass) Nil else superClass :: superClass.superClasses)
+  lazy val superClasses: Set[ClassInfo] =
+    (if (this === ClassInfo.ObjectClass) Set.empty else (superClass.superClasses + superClass))
 
   def lookupClassFields(name: String): Iterator[MemberInfo] =
     (Iterator.single(this) ++ superClasses.iterator) flatMap (_.fields.get(name))
@@ -169,12 +176,12 @@ abstract class ClassInfo(val owner: PackageInfo) extends HasDeclarationName with
 
   /** All traits inherited directly or indirectly by this class */
   lazy val allTraits: Set[ClassInfo] =
-    if (this == ClassInfo.ObjectClass) Set.empty
+    if (this === ClassInfo.ObjectClass) Set.empty
     else superClass.allTraits ++ directTraits
 
   /** All interfaces inherited directly or indirectly by this class */
   lazy val allInterfaces: Set[ClassInfo] =
-    if (this == ClassInfo.ObjectClass) Set.empty
+    if (this === ClassInfo.ObjectClass) Set.empty
     else superClass.allInterfaces ++ interfaces ++ (interfaces flatMap (_.allInterfaces))
 
   private def unimplemented(sel: ClassInfo => Traversable[MemberInfo]): List[MemberInfo] = {

reporter/src/main/scala/com/typesafe/tools/mima/lib/analyze/template/TemplateRules.scala

@@ -43,12 +43,8 @@ import com.typesafe.tools.mima.lib.analyze.Rule
   }
 
   private[TemplateRules] trait ClassTypesHelper {
-    def diff(thisTypes: Iterable[ClassInfo], thatTypes: Iterable[ClassInfo]) = {
-      val thisSuperclasses = thisTypes.map(_.fullName).toSet
-      val thatSuperclasses = thisTypes.map(_.fullName).toSet
-
-      thisTypes.filter(sc => !thatTypes.exists(_.fullName == sc.fullName))
-    }
+    def diff(thisTypes: Set[ClassInfo], thatTypes: Set[ClassInfo]) =
+      thisTypes.filter(sc => !thatTypes.exists(_ === sc))
   }
 
   object Superclasses extends TemplateRule with ClassTypesHelper {