Make sure Generic values get updated according to expected type in some cases

src/main/scala/leon/codegen/CompilationUnit.scala

@@ -213,8 +213,9 @@ class CompilationUnit(val ctx: LeonContext,
       }
       Tuple(elems)
 
-    case (gv : GenericValue, _: TypeParameter) =>
-      gv
+    case (gv @ GenericValue(gtp, id), tp: TypeParameter) =>
+      if (gtp == tp) gv
+      else GenericValue(tp, id).copiedFrom(gv)
 
     case (set : runtime.Set, SetType(b)) =>
       FiniteSet(set.getElements().asScala.map(jvmToExpr(_, b)).toSet).setType(SetType(b))

src/main/scala/leon/purescala/TypeTreeOps.scala

@@ -302,6 +302,14 @@ object TypeTreeOps {
           case Error(tpe, desc) =>
             Error(tpeSub(tpe), desc).copiedFrom(e)
           
+          case g @ GenericValue(tpar, id) =>
+            tpeSub(tpar) match {
+              case newTpar : TypeParameter => 
+                GenericValue(newTpar, id).copiedFrom(g)
+              case other => // FIXME any better ideas?
+                sys.error(s"Tried to substitute $tpar with $other within GenericValue $g")
+            }
+          
           case ens @ Ensuring(body, id, pred) =>
             val newId = freshId(id, tpeSub(id.getType))
             Ensuring(srec(body), newId, rec(idsMap + (id -> newId))(pred)).copiedFrom(ens)