SI-10071 Separate compilation for varargs methods

Make sure that methods annotated with varargs are properly mixed-in. This commit
splits the transformation into an info transformer (that works on all symbols, whether
they come from source or binary) and a tree transformer.

The gist of this is that the symbol-creation part of the code was moved to the UnCurry
info transformer, while tree operations remained in the tree transformer. The newly
created symbol is attached to the original method so that the tree transformer can still
retrieve the symbol.

A few fall outs:

- I removed a local map that was identical to TypeParamsVarargsAttachment
- moved the said attachment to StdAttachments so it’s visible between reflect.internal
  and nsc.transform
- a couple more comments in UnCurry to honour the boy-scout rule

2 files changed, 34 insertions, 62 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Erasure.scala b/src/compiler/scala/tools/nsc/transform/Erasure.scala
index 25475515aa..92accaf9dd 100644
--- a/src/compiler/scala/tools/nsc/transform/Erasure.scala
+++ b/src/compiler/scala/tools/nsc/transform/Erasure.scala
@@ -1278,5 +1278,4 @@ abstract class Erasure extends InfoTransform
   }
 
   private class TypeRefAttachment(val tpe: TypeRef)
-  class TypeParamVarargsAttachment(val typeParamRef: Type)
 }
diff --git a/src/compiler/scala/tools/nsc/transform/UnCurry.scala b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
index d8fa7b58e8..ea3c7da014 100644
--- a/src/compiler/scala/tools/nsc/transform/UnCurry.scala
+++ b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
@@ -27,6 +27,8 @@ import scala.reflect.internal.util.ListOfNil
  *  - for every repeated Scala parameter `x: T*' --> x: Seq[T].
  *  - for every repeated Java parameter `x: T...' --> x: Array[T], except:
  *    if T is an unbounded abstract type, replace --> x: Array[Object]
+ *  - for every method defining repeated parameters annotated with @varargs, generate
+ *    a synthetic Java-style vararg method
  *  - for every argument list that corresponds to a repeated Scala parameter
  *       (a_1, ..., a_n) => (Seq(a_1, ..., a_n))
  *  - for every argument list that corresponds to a repeated Java parameter
@@ -44,6 +46,8 @@ import scala.reflect.internal.util.ListOfNil
  *          def liftedTry$1 = try { x_i } catch { .. }
  *          meth(x_1, .., liftedTry$1(), .. )
  *        }
+ *  - remove calls to elidable methods and replace their bodies with NOPs when elide-below
+ *    requires it
  */
 /*</export> */
 abstract class UnCurry extends InfoTransform
@@ -577,7 +581,13 @@ abstract class UnCurry extends InfoTransform
               case None    => literalRhsIfConst
             }
           )
-          addJavaVarargsForwarders(dd, flatdd)
+          // Only class members can reasonably be called from Java due to name mangling.
+          // Additionally, the Uncurry info transformer only adds a forwarder symbol to class members,
+          // since the other symbols are not part of the ClassInfoType (see reflect.internal.transform.UnCurry)
+          if (dd.symbol.owner.isClass)
+            addJavaVarargsForwarders(dd, flatdd)
+          else
+            flatdd
 
         case tree: Try =>
           if (tree.catches exists (cd => !treeInfo.isCatchCase(cd)))
@@ -739,68 +749,32 @@ abstract class UnCurry extends InfoTransform
         if (!hasRepeated) reporter.error(dd.symbol.pos, "A method without repeated parameters cannot be annotated with the `varargs` annotation.")
       }
 
-    /* Called during post transform, after the method argument lists have been flattened.
-     * It looks for the method in the `repeatedParams` map, and generates a Java-style
+    /**
+     * Called during post transform, after the method argument lists have been flattened.
+     * It looks for the forwarder symbol in the symbol attachments and generates a Java-style
      * varargs forwarder.
+     *
+     * @note The Java-style varargs method symbol is generated in the Uncurry info transformer. If the
+     *       symbol can't be found this method reports a warning and carries on.
+     * @see  [[scala.reflect.internal.transform.UnCurry]]
      */
     private def addJavaVarargsForwarders(dd: DefDef, flatdd: DefDef): DefDef = {
       if (!dd.symbol.hasAnnotation(VarargsClass) || !enteringUncurry(mexists(dd.symbol.paramss)(sym => definitions.isRepeatedParamType(sym.tpe))))
         return flatdd
 
-      val forwSym = currentClass.newMethod(dd.name.toTermName, dd.pos, VARARGS | SYNTHETIC | flatdd.symbol.flags & ~DEFERRED)
-
-      val isRepeated = enteringUncurry(dd.symbol.info.paramss.flatten.map(sym => definitions.isRepeatedParamType(sym.tpe)))
-
-      val oldPs = flatdd.symbol.paramss.head
-
-      // see comment in method toArrayType below
-      val arrayTypesMappedToObject = mutable.Map.empty[Symbol, Type]
-
-      val forwTpe = {
-        val (oldTps, tps) = dd.symbol.tpe match {
-          case PolyType(oldTps, _) =>
-            val newTps = oldTps.map(_.cloneSymbol(forwSym))
-            (oldTps, newTps)
-
-          case _ => (Nil, Nil)
-        }
-
-        def toArrayType(tp: Type, newParam: Symbol): Type = {
-          val arg = elementType(SeqClass, tp)
-          val elem = if (arg.typeSymbol.isTypeParameterOrSkolem && !(arg <:< AnyRefTpe)) {
-            // To prevent generation of an `Object` parameter from `Array[T]` parameter later
-            // as this would crash the Java compiler which expects an `Object[]` array for varargs
-            //   e.g.        def foo[T](a: Int, b: T*)
-            //   becomes     def foo[T](a: Int, b: Array[Object])
-            //   instead of  def foo[T](a: Int, b: Array[T]) ===> def foo[T](a: Int, b: Object)
-            //
-            // In order for the forwarder method to type check we need to insert a cast:
-            //   def foo'[T'](a: Int, b: Array[Object]) = foo[T'](a, wrapRefArray(b).asInstanceOf[Seq[T']])
-            // The target element type for that cast (T') is stored in the `arrayTypesMappedToObject` map.
-            val originalArg = arg.substSym(oldTps, tps)
-            arrayTypesMappedToObject(newParam) = originalArg
-            // Store the type parameter that was replaced by Object to emit the correct generic signature
-            newParam.updateAttachment(new erasure.TypeParamVarargsAttachment(originalArg))
-            ObjectTpe
-          } else
-            arg
-          arrayType(elem)
+      val forwSym: Symbol = {
+        currentClass.info // make sure the info is up to date, so the varargs forwarder symbol has been generated
+        flatdd.symbol.attachments.get[VarargsSymbolAttachment] match {
+          case Some(VarargsSymbolAttachment(sym)) => sym
+          case None =>
+            reporter.warning(dd.pos, s"Could not generate Java varargs forwarder for ${flatdd.symbol}. Please file a bug.")
+            return flatdd
         }
-
-        val ps = map2(oldPs, isRepeated)((oldParam, isRep) => {
-          val newParam = oldParam.cloneSymbol(forwSym)
-          val tp = if (isRep) toArrayType(oldParam.tpe, newParam) else oldParam.tpe
-          newParam.setInfo(tp)
-        })
-
-        val resTp = dd.symbol.tpe_*.finalResultType.substSym(oldPs, ps)
-        val mt = MethodType(ps, resTp)
-        val r = if (tps.isEmpty) mt else PolyType(tps, mt)
-        r.substSym(oldTps, tps)
       }
 
-      forwSym.setInfo(forwTpe)
-      val newPs = forwTpe.params
+      val newPs = forwSym.tpe.params
+      val isRepeated = enteringUncurry(dd.symbol.info.paramss.flatten.map(sym => definitions.isRepeatedParamType(sym.tpe)))
+      val oldPs = flatdd.symbol.paramss.head
 
       val theTyper = typer.atOwner(dd, currentClass)
       val forwTree = theTyper.typedPos(dd.pos) {
@@ -809,8 +783,8 @@ abstract class UnCurry extends InfoTransform
           else {
             val parTp = elementType(ArrayClass, param.tpe)
             val wrap = gen.mkWrapArray(Ident(param), parTp)
-            arrayTypesMappedToObject.get(param) match {
-              case Some(tp) => gen.mkCast(wrap, seqType(tp))
+            param.attachments.get[TypeParamVarargsAttachment] match {
+              case Some(TypeParamVarargsAttachment(tp)) => gen.mkCast(wrap, seqType(tp))
               case _ => wrap
             }
           }
@@ -821,13 +795,12 @@ abstract class UnCurry extends InfoTransform
       }
 
       // check if the method with that name and those arguments already exists in the template
-      currentClass.info.member(forwSym.name).alternatives.find(s => s != forwSym && s.tpe.matches(forwSym.tpe)) match {
-        case Some(s) => reporter.error(dd.symbol.pos,
-                                   "A method with a varargs annotation produces a forwarder method with the same signature "
-                                   + s.tpe + " as an existing method.")
+      enteringUncurry(currentClass.info.member(forwSym.name).alternatives.find(s => s != forwSym && s.tpe.matches(forwSym.tpe))) match {
+        case Some(s) =>
+          reporter.error(dd.symbol.pos,
+            s"A method with a varargs annotation produces a forwarder method with the same signature ${s.tpe} as an existing method.")
         case None =>
           // enter symbol into scope
-          currentClass.info.decls enter forwSym
           addNewMember(forwTree)
       }