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

5 files changed, 121 insertions, 66 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Erasure.scala b/src/compiler/scala/tools/nsc/transform/Erasure.scala
index a7cf6d9e8d..7a06c0cf2c 100644
--- a/src/compiler/scala/tools/nsc/transform/Erasure.scala
+++ b/src/compiler/scala/tools/nsc/transform/Erasure.scala
@@ -1189,5 +1189,4 @@ abstract class Erasure extends AddInterfaces
   }
 
   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 17f4471533..d5a7213cfb 100644
--- a/src/compiler/scala/tools/nsc/transform/UnCurry.scala
+++ b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
@@ -26,6 +26,8 @@ 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
@@ -43,6 +45,8 @@ 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
@@ -593,7 +597,13 @@ abstract class UnCurry extends InfoTransform
               case None    => newRhs
             }
           )
-          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)))
@@ -684,7 +694,7 @@ abstract class UnCurry extends InfoTransform
               // declared type and assign this to a synthetic val. Later, we'll patch
               // the method body to refer to this, rather than the parameter.
               val tempVal: ValDef = {
-                // SI-9442: using the "uncurry-erased" type (the one after the uncurry phase) can lead to incorrect 
+                // SI-9442: using the "uncurry-erased" type (the one after the uncurry phase) can lead to incorrect
                 // tree transformations. For example, compiling:
                 // ```
                 //   def foo(c: Ctx)(l: c.Tree): Unit = {
@@ -713,7 +723,7 @@ abstract class UnCurry extends InfoTransform
                 //    to redo this desugaring manually here
                 // 2. the type needs to be normalized, since `gen.mkCast` checks this (no HK here, just aliases have
                 //    to be expanded before handing the type to `gen.mkAttributedCast`, which calls `gen.mkCast`)
-                val info0 = 
+                val info0 =
                   enteringUncurry(p.symbol.info) match {
                     case DesugaredParameterType(desugaredTpe) =>
                       desugaredTpe
@@ -755,68 +765,32 @@ 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)
-
-      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) {
@@ -825,8 +799,8 @@ 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
             }
           }
@@ -837,13 +811,12 @@ 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)
       }
 
diff --git a/src/reflect/scala/reflect/internal/StdAttachments.scala b/src/reflect/scala/reflect/internal/StdAttachments.scala
index 3df31b538c..cddb0c8f72 100644
--- a/src/reflect/scala/reflect/internal/StdAttachments.scala
+++ b/src/reflect/scala/reflect/internal/StdAttachments.scala
@@ -58,4 +58,7 @@ trait StdAttachments {
     * error to indicate that the earlier observation was incomplete.
     */
   case object KnownDirectSubclassesCalled extends PlainAttachment
+
+  /** An attachment carrying information between uncurry and erasure */
+  case class TypeParamVarargsAttachment(val typeParamRef: Type)
 }
diff --git a/src/reflect/scala/reflect/internal/transform/UnCurry.scala b/src/reflect/scala/reflect/internal/transform/UnCurry.scala
index 85e3ac60e8..e86003226a 100644
--- a/src/reflect/scala/reflect/internal/transform/UnCurry.scala
+++ b/src/reflect/scala/reflect/internal/transform/UnCurry.scala
@@ -4,6 +4,7 @@ package internal
 package transform
 
 import Flags._
+import scala.collection.mutable
 
 trait UnCurry {
 
@@ -11,6 +12,12 @@ trait UnCurry {
   import global._
   import definitions._
 
+  /**
+   * The synthetic Java vararg method symbol corresponding to a Scala vararg method
+   * annotated with @varargs.
+   */
+  case class VarargsSymbolAttachment(varargMethod: Symbol)
+
   /** Note: changing tp.normalize to tp.dealias in this method leads to a single
    *  test failure: run/t5688.scala, where instead of the expected output
    *    Vector(ta, tb, tab)
@@ -67,8 +74,25 @@ trait UnCurry {
       tp match {
         case ClassInfoType(parents, decls, clazz) =>
           val parents1 = parents mapConserve uncurry
-          if (parents1 eq parents) tp
-          else ClassInfoType(parents1, decls, clazz) // @MAT normalize in decls??
+          val varargOverloads = mutable.ListBuffer.empty[Symbol]
+
+          // Not using `hasAnnotation` here because of dreaded cyclic reference errors:
+          // it may happen that VarargsClass has not been initialized yet and we get here
+          // while processing one of its superclasses (such as java.lang.Object). Since we
+          // don't need the more precise `matches` semantics, we only check the symbol, which
+          // is anyway faster and safer
+          for (decl <- decls if decl.annotations.exists(_.symbol == VarargsClass)) {
+            if (mexists(decl.paramss)(sym => definitions.isRepeatedParamType(sym.tpe))) {
+              val forwarderSym = varargForwarderSym(clazz, decl, exitingPhase(phase)(decl.info))
+              varargOverloads += forwarderSym
+            }
+          }
+          if ((parents1 eq parents) && varargOverloads.isEmpty) tp
+          else {
+            val newDecls = decls.cloneScope
+            varargOverloads.foreach(newDecls.enter)
+            ClassInfoType(parents1, newDecls, clazz)
+          } // @MAT normalize in decls??
         case PolyType(_, _) =>
           mapOver(tp)
         case _ =>
@@ -77,6 +101,60 @@ trait UnCurry {
     }
   }
 
+  private def varargForwarderSym(currentClass: Symbol, origSym: Symbol, newInfo: Type): Symbol = {
+    val forwSym = currentClass.newMethod(origSym.name.toTermName, origSym.pos, VARARGS | SYNTHETIC | origSym.flags & ~DEFERRED)
+
+    // we are using `origSym.info`, which contains the type *before* the transformation
+    // so we still see repeated parameter types (uncurry replaces them with Seq)
+    val isRepeated = origSym.info.paramss.flatten.map(sym => definitions.isRepeatedParamType(sym.tpe))
+    val oldPs = newInfo.paramss.head
+
+    val forwTpe = {
+      val (oldTps, tps) = newInfo 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  TypeParamVarargsAttachment
+          val originalArg = arg.substSym(oldTps, tps)
+          // Store the type parameter that was replaced by Object to emit the correct generic signature
+          newParam.updateAttachment(new TypeParamVarargsAttachment(originalArg))
+          ObjectTpe
+        } else
+          arg
+        arrayType(elem)
+      }
+
+      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 = newInfo.finalResultType.substSym(oldPs, ps)
+      val mt = MethodType(ps, resTp)
+      val r = if (tps.isEmpty) mt else PolyType(tps, mt)
+      r.substSym(oldTps, tps)
+    }
+
+    origSym.updateAttachment(VarargsSymbolAttachment(forwSym))
+    forwSym.setInfo(forwTpe)
+  }
+
   /** - return symbol's transformed type,
    *  - if symbol is a def parameter with transformed type T, return () => T
    *
diff --git a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
index 8481cd8996..45dd550e3e 100644
--- a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
+++ b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
@@ -42,6 +42,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     this.SyntheticUnitAttachment
     this.SubpatternsAttachment
     this.KnownDirectSubclassesCalled
+    this.TypeParamVarargsAttachment
     this.noPrint
     this.typeDebug
     this.Range
@@ -444,6 +445,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     definitions.ScalaValueClassesNoUnit
     definitions.ScalaValueClasses
 
+    uncurry.VarargsSymbolAttachment
     uncurry.DesugaredParameterType
     erasure.GenericArray
     erasure.scalaErasure