closes #3486.

fixed by having mixin do the cloning at the beginning of erasure and
then updating the symbol's info to transform it to be valid in current
phase

review by odersky

2 files changed, 18 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/Symbols.scala b/src/compiler/scala/tools/nsc/symtab/Symbols.scala
index 1908b4ded9..e386508bdd 100644
--- a/src/compiler/scala/tools/nsc/symtab/Symbols.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Symbols.scala
@@ -776,6 +776,7 @@ trait Symbols extends reflect.generic.Symbols { self: SymbolTable =>
       assert(phaseId(infos.validFrom) <= phase.id)
       if (phaseId(infos.validFrom) == phase.id) infos = infos.prev
       infos = TypeHistory(currentPeriod, info, infos)
+      validTo = if (info.isComplete) currentPeriod else NoPeriod
       this
     }
 
diff --git a/src/compiler/scala/tools/nsc/transform/Mixin.scala b/src/compiler/scala/tools/nsc/transform/Mixin.scala
index c228ee0e46..d1b3142c8a 100644
--- a/src/compiler/scala/tools/nsc/transform/Mixin.scala
+++ b/src/compiler/scala/tools/nsc/transform/Mixin.scala
@@ -231,12 +231,27 @@ abstract class Mixin extends InfoTransform with ast.TreeDSL {
         for (member <- impl.info.decls.toList) {
           if (isForwarded(member)) {
             val imember = member.overriddenSymbol(iface)
-            //Console.println("mixin member "+member+":"+member.tpe+member.locationString+" "+imember+" "+imember.overridingSymbol(clazz)+" to "+clazz+" with scope "+clazz.info.decls)//DEBUG
+            // atPhase(currentRun.erasurePhase){
+            //   println(""+(clazz, iface, clazz.typeParams, iface.typeParams, imember, clazz.thisType.baseType(iface), clazz.thisType.baseType(iface).memberInfo(imember), imember.info substSym(iface.typeParams, clazz.typeParams)  ))
+            // }
+            // Console.println("mixin member "+member+":"+member.tpe+member.locationString+" "+imember+" "+imember.overridingSymbol(clazz)+" to "+clazz+" with scope "+clazz.info.decls)//DEBUG
             if (imember.overridingSymbol(clazz) == NoSymbol &&
                 clazz.info.findMember(member.name, 0, lateDEFERRED, false).alternatives.contains(imember)) {
+                  val newSym = atPhase(currentRun.erasurePhase){
+                      val res = imember.cloneSymbol(clazz)
+                      // since we used the member (imember) from the interface that represents the trait that's being mixed in,
+                      // have to instantiate the interface type params (that may occur in imember's info) as they are seen from the class
+                      // we can't use the member that we get from the implementation class, as it's a clone that was made after erasure,
+                      // and thus it does not know its info at the beginning of erasure anymore
+                      // optimize: no need if iface has no typeparams
+                      if(iface.typeParams nonEmpty) res.setInfo(clazz.thisType.baseType(iface).memberInfo(imember))
+                      res
+                    } // clone before erasure got rid of type info we'll need to generate a javaSig
+                  // now we'll have the type info at (the beginning of) erasure in our history,
+                  newSym.updateInfo(imember.info.cloneInfo(newSym)) // and now newSym has the info that's been transformed to fit this period (no need for asSeenFrom as phase.erasedTypes)
                   val member1 = addMember(
                     clazz,
-                    member.cloneSymbol(clazz) setPos clazz.pos resetFlag (DEFERRED | lateDEFERRED))
+                    newSym setPos clazz.pos resetFlag (DEFERRED | lateDEFERRED))
                   member1.asInstanceOf[TermSymbol] setAlias member;
                 }
           }