Fix #442: Name hash of value class should include underlying type

internal/compiler-bridge/src/main/scala/xsbt/ExtractAPI.scala

@@ -359,7 +359,16 @@ class ExtractAPI[GlobalType <: Global](
    * TODO: can we include hashes for parent classes instead? This seems a bit messy.
    */
   private def mkStructureWithInherited(info: Type, s: Symbol): xsbti.api.Structure = {
-    val ancestorTypes = linearizedAncestorTypes(info)
+    val ancestorTypes0 = linearizedAncestorTypes(info)
+    val ancestorTypes =
+      if (s.isDerivedValueClass) {
+        val underlying = s.derivedValueClassUnbox.tpe.finalResultType
+        // The underlying type of a value class should be part of the name hash
+        // of the value class (see the test `value-class-underlying`), this is accomplished
+        // by adding the underlying type to the list of parent types.
+        underlying :: ancestorTypes0
+      } else
+        ancestorTypes0
     val decls = info.decls.toList
     val declsNoModuleCtor = if (s.isModuleClass) removeConstructors(decls) else decls
     val declSet = decls.toSet

zinc/src/sbt-test/source-dependencies/value-class-underlying/C.scala

@@ -1,6 +1,6 @@
 object C {
   def main(args: Array[String]): Unit = {
-    val x = B.foo
-    println("x: " + x) // Need to use x in an expression to see if it crashes or not
+    val duck = B.foo
+    println("duck: " + duck) // Need to use duck in an expression to see if it crashes or not
   }
 }