From 107cb5d2148b83e77d0dac87ea136e4d3a6f9a9c Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Wed, 1 Jul 2020 17:47:40 +0200
Subject: [PATCH 01/12] Generate varargs bridge with the right flags on
 `@varargs` annotation

---
 .../dotty/tools/dotc/core/Definitions.scala   |  1 +
 .../tools/dotc/transform/ElimRepeated.scala   | 69 ++++++++++---------
 .../test/dotc/run-test-pickling.blacklist     |  1 +
 tests/run/i7212/CompatVargs.scala             | 11 +++
 tests/run/i7212/Test.java                     |  9 +++
 5 files changed, 60 insertions(+), 31 deletions(-)
 create mode 100644 tests/run/i7212/CompatVargs.scala
 create mode 100644 tests/run/i7212/Test.java

diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index 875916c62a39..49f281c6521f 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -829,6 +829,7 @@ class Definitions {
   @tu lazy val FunctionalInterfaceAnnot: ClassSymbol = ctx.requiredClass("java.lang.FunctionalInterface")
   @tu lazy val InfixAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.infix")
   @tu lazy val AlphaAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.alpha")
+  @tu lazy val VarargsAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.varargs")
 
   // A list of annotations that are commonly used to indicate that a field/method argument or return
   // type is not null. These annotations are used by the nullification logic in JavaNullInterop to
diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index 069575176bea..713e7b861bc9 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -34,34 +34,34 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     elimRepeated(tp)
 
   override def transform(ref: SingleDenotation)(using Context): SingleDenotation =
-    super.transform(ref) match {
+    super.transform(ref) match
       case ref1: SymDenotation if (ref1 ne ref) && overridesJava(ref1.symbol) =>
         // This method won't override the corresponding Java method at the end of this phase,
         // only the bridge added by `addVarArgsBridge` will.
         ref1.copySymDenotation(initFlags = ref1.flags &~ Override)
       case ref1 =>
         ref1
-    }
 
   override def mayChange(sym: Symbol)(using Context): Boolean = sym.is(Method)
 
   private def overridesJava(sym: Symbol)(using Context) = sym.allOverriddenSymbols.exists(_.is(JavaDefined))
 
-  private def elimRepeated(tp: Type)(using Context): Type = tp.stripTypeVar match {
+  private def hasVargsAnnotation(sym: Symbol)(using ctx: Context) = sym.hasAnnotation(defn.VarargsAnnot)
+
+  /** Eliminate repeated parameters from method types. */
+  private def elimRepeated(tp: Type)(using Context): Type = tp.stripTypeVar match
     case tp @ MethodTpe(paramNames, paramTypes, resultType) =>
       val resultType1 = elimRepeated(resultType)
       val paramTypes1 =
-        if (paramTypes.nonEmpty && paramTypes.last.isRepeatedParam) {
+        if paramTypes.nonEmpty && paramTypes.last.isRepeatedParam then
           val last = paramTypes.last.translateFromRepeated(toArray = tp.isJavaMethod)
           paramTypes.init :+ last
-        }
         else paramTypes
       tp.derivedLambdaType(paramNames, paramTypes1, resultType1)
     case tp: PolyType =>
       tp.derivedLambdaType(tp.paramNames, tp.paramInfos, elimRepeated(tp.resultType))
     case tp =>
       tp
-  }
 
   def transformTypeOfTree(tree: Tree)(using Context): Tree =
     tree.withType(elimRepeated(tree.tpe))
@@ -72,35 +72,35 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   override def transformSelect(tree: Select)(using Context): Tree =
     transformTypeOfTree(tree)
 
-  override def transformApply(tree: Apply)(using Context): Tree = {
+  override def transformApply(tree: Apply)(using Context): Tree =
     val args = tree.args.mapConserve {
       case arg: Typed if isWildcardStarArg(arg) =>
         val isJavaDefined = tree.fun.symbol.is(JavaDefined)
         val tpe = arg.expr.tpe
-        if (isJavaDefined && tpe.derivesFrom(defn.SeqClass))
+        if isJavaDefined && tpe.derivesFrom(defn.SeqClass) then
           seqToArray(arg.expr)
-        else if (!isJavaDefined && tpe.derivesFrom(defn.ArrayClass))
+        else if !isJavaDefined && tpe.derivesFrom(defn.ArrayClass)
           arrayToSeq(arg.expr)
         else
           arg.expr
       case arg => arg
     }
     transformTypeOfTree(cpy.Apply(tree)(tree.fun, args))
-  }
 
   /** Convert sequence argument to Java array */
-  private def seqToArray(tree: Tree)(using Context): Tree = tree match {
+  private def seqToArray(tree: Tree)(using Context): Tree = tree match
     case SeqLiteral(elems, elemtpt) =>
       JavaSeqLiteral(elems, elemtpt)
     case _ =>
       val elemType = tree.tpe.elemType
       var elemClass = erasure(elemType).classSymbol
-      if (defn.NotRuntimeClasses.contains(elemClass)) elemClass = defn.ObjectClass
+      if defn.NotRuntimeClasses.contains(elemClass) then
+        elemClass = defn.ObjectClass
+      end if
       ref(defn.DottyArraysModule)
         .select(nme.seqToArray)
         .appliedToType(elemType)
         .appliedTo(tree, clsOf(elemClass.typeRef))
-  }
 
   /** Convert Java array argument to Scala Seq */
   private def arrayToSeq(tree: Tree)(using Context): Tree =
@@ -109,36 +109,44 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   override def transformTypeApply(tree: TypeApply)(using Context): Tree =
     transformTypeOfTree(tree)
 
-  /** If method overrides a Java varargs method, add a varargs bridge.
-   *  Also transform trees inside method annotation
+  /** If method overrides a Java varargs method or is annotated with @varargs, add a varargs bridge.
+   *  Also transform trees inside method annotation.
    */
   override def transformDefDef(tree: DefDef)(using Context): Tree =
     atPhase(thisPhase) {
-      if (tree.symbol.info.isVarArgsMethod && overridesJava(tree.symbol))
-        addVarArgsBridge(tree)
+      val isOverride = overridesJava(tree.symbol)
+      val hasAnnotation = hasVargsAnnotation(tree.symbol)
+      if tree.symbol.info.isVarArgsMethod && (isOverride || hasAnnotation) then
+        // non-overrides need the varargs bytecode flag and cannot be synthetic
+        // otherwise javac refuses to call them.
+        addVarArgsBridge(tree, isOverride)
       else
         tree
     }
 
   /** Add a Java varargs bridge
-   *  @param  ddef  the original method definition which is assumed to override
-   *                a Java varargs method JM up to this phase.
-   *  @return  a thicket consisting of `ddef` and a varargs bridge method
-   *           which overrides the Java varargs method JM from this phase on
-   *           and forwards to `ddef`.
+   *  @param  ddef   the original method definition
+   *  @param addFlag the flag to add to the method symbol
+
+   *  @return a thicket consisting of `ddef` and a varargs bridge method
+   *          which forwards java varargs to `ddef`. It retains all the
+   *          flags of `ddef` except `Private`.
    *
-   *  A bridge is necessary because the following hold
+   *  A bridge is necessary because the following hold:
    *    - the varargs in `ddef` will change from `RepeatedParam[T]` to `Seq[T]` after this phase
-   *    - _but_ the callers of `ddef` expect its varargs to be changed to `Array[? <: T]`, since it overrides
-   *      a Java varargs
+   *    - _but_ the callers of `ddef` expect its varargs to be changed to `Array[? <: T]`
    *  The solution is to add a "bridge" method that converts its argument from `Array[? <: T]` to `Seq[T]` and
    *  forwards it to `ddef`.
    */
-  private def addVarArgsBridge(ddef: DefDef)(using Context): Tree = {
+  private def addVarArgsBridge(ddef: DefDef, synthetic: Boolean)(using Context): Tree =
     val original = ddef.symbol.asTerm
+    // For simplicity we always set the varargs flag
+    val flags = ddef.symbol.flags | JavaVarargs &~ Private
     val bridge = original.copy(
-      flags = ddef.symbol.flags &~ Private | Artifact,
-      info = toJavaVarArgs(ddef.symbol.info)).enteredAfter(thisPhase).asTerm
+        flags = if synthetic then flags | Artifact else flags,
+        info = toJavaVarArgs(ddef.symbol.info)
+      ).enteredAfter(thisPhase).asTerm
+
     val bridgeDef = polyDefDef(bridge, trefs => vrefss => {
       val (vrefs :+ varArgRef) :: vrefss1 = vrefss
       // Can't call `.argTypes` here because the underlying array type is of the
@@ -151,15 +159,14 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     })
 
     Thicket(ddef, bridgeDef)
-  }
 
   /** Convert type from Scala to Java varargs method */
-  private def toJavaVarArgs(tp: Type)(using Context): Type = tp match {
+  private def toJavaVarArgs(tp: Type)(using Context): Type = tp match
     case tp: PolyType =>
       tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(tp.resultType))
     case tp: MethodType =>
       val inits :+ last = tp.paramInfos
       val last1 = last.translateFromRepeated(toArray = true)
       tp.derivedLambdaType(tp.paramNames, inits :+ last1, tp.resultType)
-  }
+
 }
diff --git a/compiler/test/dotc/run-test-pickling.blacklist b/compiler/test/dotc/run-test-pickling.blacklist
index ebcf2b861abe..b69d517ca893 100644
--- a/compiler/test/dotc/run-test-pickling.blacklist
+++ b/compiler/test/dotc/run-test-pickling.blacklist
@@ -26,3 +26,4 @@ i7868.scala
 enum-java
 zero-arity-case-class.scala
 tuple-ops.scala
+i7212
diff --git a/tests/run/i7212/CompatVargs.scala b/tests/run/i7212/CompatVargs.scala
new file mode 100644
index 000000000000..0269d27c5841
--- /dev/null
+++ b/tests/run/i7212/CompatVargs.scala
@@ -0,0 +1,11 @@
+import scala.annotation._
+
+class CompatVargs {
+  @varargs
+  def vargs(args: String*): Unit = println(args)
+
+  def vargsFromScala(): Unit =
+    vargs("single")
+    vargs("a", "b")
+    vargs(Seq("a", "b"): _*)
+}
diff --git a/tests/run/i7212/Test.java b/tests/run/i7212/Test.java
new file mode 100644
index 000000000000..e2d21bd76dfd
--- /dev/null
+++ b/tests/run/i7212/Test.java
@@ -0,0 +1,9 @@
+public class Test {
+    public static void main(String[] args) {
+        CompatVargs c = new CompatVargs();
+        c.vargs("single");
+        c.vargs("a", "b");
+        c.vargs(new String[]{"a", "b"});
+        c.vargsFromScala();
+    }
+}

From f3c4f8c5fe40257d116946780df8abc08909693b Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Thu, 2 Jul 2020 15:53:30 +0200
Subject: [PATCH 02/12] Check parent methods for varargs annotation

---
 .../tools/dotc/transform/ElimRepeated.scala   | 39 ++++++++++++++-----
 .../test/dotc/run-test-pickling.blacklist     |  1 +
 tests/run/varargs-abstract/Test.java          | 19 +++++++++
 tests/run/varargs-abstract/test.scala         | 18 +++++++++
 4 files changed, 67 insertions(+), 10 deletions(-)
 create mode 100644 tests/run/varargs-abstract/Test.java
 create mode 100644 tests/run/varargs-abstract/test.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index 713e7b861bc9..667516cc97b5 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -46,7 +46,9 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
 
   private def overridesJava(sym: Symbol)(using Context) = sym.allOverriddenSymbols.exists(_.is(JavaDefined))
 
-  private def hasVargsAnnotation(sym: Symbol)(using ctx: Context) = sym.hasAnnotation(defn.VarargsAnnot)
+  private def hasVarargsAnnotation(sym: Symbol)(using Context) = sym.hasAnnotation(defn.VarargsAnnot)
+
+  private def parentHasAnnotation(sym: Symbol)(using Context) = sym.allOverriddenSymbols.exists(hasVarargsAnnotation)
 
   /** Eliminate repeated parameters from method types. */
   private def elimRepeated(tp: Type)(using Context): Type = tp.stripTypeVar match
@@ -114,8 +116,9 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
    */
   override def transformDefDef(tree: DefDef)(using Context): Tree =
     atPhase(thisPhase) {
-      val isOverride = overridesJava(tree.symbol)
-      val hasAnnotation = hasVargsAnnotation(tree.symbol)
+      val sym = tree.symbol
+      val isOverride = overridesJava(sym)
+      val hasAnnotation = hasVarargsAnnotation(sym) || parentHasAnnotation(sym)
       if tree.symbol.info.isVarArgsMethod && (isOverride || hasAnnotation) then
         // non-overrides need the varargs bytecode flag and cannot be synthetic
         // otherwise javac refuses to call them.
@@ -125,7 +128,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     }
 
   /** Add a Java varargs bridge
-   *  @param  ddef   the original method definition
+   *  @param ddef    the original method definition
    *  @param addFlag the flag to add to the method symbol
 
    *  @return a thicket consisting of `ddef` and a varargs bridge method
@@ -141,6 +144,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   private def addVarArgsBridge(ddef: DefDef, synthetic: Boolean)(using Context): Tree =
     val original = ddef.symbol.asTerm
     // For simplicity we always set the varargs flag
+    // although it's not strictly necessary for overrides
     val flags = ddef.symbol.flags | JavaVarargs &~ Private
     val bridge = original.copy(
         flags = if synthetic then flags | Artifact else flags,
@@ -162,11 +166,26 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
 
   /** Convert type from Scala to Java varargs method */
   private def toJavaVarArgs(tp: Type)(using Context): Type = tp match
-    case tp: PolyType =>
-      tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(tp.resultType))
-    case tp: MethodType =>
-      val inits :+ last = tp.paramInfos
-      val last1 = last.translateFromRepeated(toArray = true)
-      tp.derivedLambdaType(tp.paramNames, inits :+ last1, tp.resultType)
+      case tp: PolyType =>
+        tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(tp.resultType))
+      case tp: MethodType =>
+        val inits :+ last = tp.paramInfos
+        val vararg = varargArrayType(last)
+        val params = inits :+ vararg
+        tp.derivedLambdaType(tp.paramNames, params, tp.resultType)
+
+  /** Translate a repeated type T* to an `Array[? <: Upper]`
+   *  such that it is compatible with java varargs.
+   *
+   *  If T is not a primitive type, we set `Upper = T & AnyRef`
+   *  to prevent the erasure of `Array[? <: Upper]` to Object,
+   *  which would break the varargs from Java.
+   */
+  private def varargArrayType(tp: Type)(using Context): Type =
+    val array = tp.translateFromRepeated(toArray = true)
+    val element = array.elemType.typeSymbol
+
+    if element.isPrimitiveValueClass then array
+    else defn.ArrayOf(TypeBounds.upper(AndType(element.typeRef, defn.AnyRefType)))
 
 }
diff --git a/compiler/test/dotc/run-test-pickling.blacklist b/compiler/test/dotc/run-test-pickling.blacklist
index b69d517ca893..aefe3b14b017 100644
--- a/compiler/test/dotc/run-test-pickling.blacklist
+++ b/compiler/test/dotc/run-test-pickling.blacklist
@@ -27,3 +27,4 @@ enum-java
 zero-arity-case-class.scala
 tuple-ops.scala
 i7212
+varargs-abstract
diff --git a/tests/run/varargs-abstract/Test.java b/tests/run/varargs-abstract/Test.java
new file mode 100644
index 000000000000..31dfcedc07a7
--- /dev/null
+++ b/tests/run/varargs-abstract/Test.java
@@ -0,0 +1,19 @@
+import java.util.Comparator;
+
+public class Test {
+  public static void main(String[] args) {
+    ClassImplementsClass c = new ClassImplementsClass();
+
+    c.x("a", "b", "c");
+    c.y("a", "b", "c");
+    c.z("a", "b", "c");
+
+    VarargAbstractClass i = new ClassImplementsClass();
+
+    i.x("a", "b", "c");
+    i.y("a", "b", "c");
+    // i.z("a", "b", "c");
+    // ClassCastException at runtime because the generated
+    // signature of z doesn't mention the type parameter (it should)
+  }
+}
diff --git a/tests/run/varargs-abstract/test.scala b/tests/run/varargs-abstract/test.scala
new file mode 100644
index 000000000000..073f8d086f28
--- /dev/null
+++ b/tests/run/varargs-abstract/test.scala
@@ -0,0 +1,18 @@
+import scala.annotation.varargs
+
+abstract class VarargAbstractClass[T] {
+  @varargs
+  def x(els: String*): Int
+
+  @varargs
+  def y(els: String*): Int
+
+  @varargs
+  def z(els: T*): Int
+}
+class ClassImplementsClass extends VarargAbstractClass[String] {
+
+  override def x(els: String*): Int = els.length
+  override def y(els: String*): Int = els.length
+  override def z(els: String*): Int = els.length
+}

From f671a0df30fed2a68581782714b6f99956749e7d Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Fri, 3 Jul 2020 01:32:04 +0200
Subject: [PATCH 03/12] Detect wrong usages of `@varargs` + tests

---
 .../tools/dotc/transform/ElimRepeated.scala   | 86 ++++++++++++++-----
 tests/neg/varargs-annot.scala                 | 27 ++++++
 tests/run/varargs-abstract/Test.java          |  2 +-
 3 files changed, 93 insertions(+), 22 deletions(-)
 create mode 100644 tests/neg/varargs-annot.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index 667516cc97b5..5e73b68a8ef7 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -68,6 +68,9 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   def transformTypeOfTree(tree: Tree)(using Context): Tree =
     tree.withType(elimRepeated(tree.tpe))
 
+  override def transformTypeApply(tree: TypeApply)(using Context): Tree =
+    transformTypeOfTree(tree)
+
   override def transformIdent(tree: Ident)(using Context): Tree =
     transformTypeOfTree(tree)
 
@@ -108,25 +111,52 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   private def arrayToSeq(tree: Tree)(using Context): Tree =
     tpd.wrapArray(tree, tree.tpe.elemType)
 
-  override def transformTypeApply(tree: TypeApply)(using Context): Tree =
-    transformTypeOfTree(tree)
-
   /** If method overrides a Java varargs method or is annotated with @varargs, add a varargs bridge.
    *  Also transform trees inside method annotation.
    */
   override def transformDefDef(tree: DefDef)(using Context): Tree =
     atPhase(thisPhase) {
       val sym = tree.symbol
-      val isOverride = overridesJava(sym)
-      val hasAnnotation = hasVarargsAnnotation(sym) || parentHasAnnotation(sym)
-      if tree.symbol.info.isVarArgsMethod && (isOverride || hasAnnotation) then
-        // non-overrides need the varargs bytecode flag and cannot be synthetic
-        // otherwise javac refuses to call them.
-        addVarArgsBridge(tree, isOverride)
+      val hasAnnotation = hasVarargsAnnotation(sym)
+      if hasRepeatedParams(sym) then
+        val isOverride = overridesJava(sym)
+        if isOverride || hasAnnotation || parentHasAnnotation(sym) then
+          // java varargs are more restrictive than scala's
+          // see https://github.com/scala/bug/issues/11714
+          if !isValidJavaVarArgs(sym.info) then
+            ctx.error("""To generate java-compatible varargs:
+                      |  - there must be a single repeated parameter
+                      |  - it must be the last argument in the last parameter list
+                      |""".stripMargin,
+              tree.sourcePos)
+            tree
+          else
+            addVarArgsBridge(tree, isOverride)
+        else
+          tree
       else
+        if hasAnnotation then
+          ctx.error("A method without repeated parameters cannot be annotated with @varargs", tree.sourcePos)
         tree
     }
 
+  /** Is there a repeated parameter in some parameter list? */
+  private def hasRepeatedParams(sym: Symbol)(using Context): Boolean =
+    sym.info.paramInfoss.flatten.exists(_.isRepeatedParam)
+
+  /** Is this the type of a method that has a repeated parameter type as
+   *  its last parameter in the last parameter list?
+   */
+  private def isValidJavaVarArgs(t: Type)(using Context): Boolean = t match
+    case mt: MethodType =>
+      val initp :+ lastp = mt.paramInfoss
+      initp.forall(_.forall(!_.isRepeatedParam)) &&
+      lastp.nonEmpty &&
+      lastp.init.forall(!_.isRepeatedParam) &&
+      lastp.last.isRepeatedParam
+    case _ => false
+
+
   /** Add a Java varargs bridge
    *  @param ddef    the original method definition
    *  @param addFlag the flag to add to the method symbol
@@ -141,38 +171,52 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
    *  The solution is to add a "bridge" method that converts its argument from `Array[? <: T]` to `Seq[T]` and
    *  forwards it to `ddef`.
    */
-  private def addVarArgsBridge(ddef: DefDef, synthetic: Boolean)(using Context): Tree =
+  private def addVarArgsBridge(ddef: DefDef, javaOverride: Boolean)(using ctx: Context): Tree =
     val original = ddef.symbol.asTerm
     // For simplicity we always set the varargs flag
     // although it's not strictly necessary for overrides
-    val flags = ddef.symbol.flags | JavaVarargs &~ Private
+    // (but it is for non-overrides)
+    val flags = ddef.symbol.flags | JavaVarargs
     val bridge = original.copy(
-        flags = if synthetic then flags | Artifact else flags,
+        // non-overrides cannot be synthetic otherwise javac refuses to call them
+        flags = if javaOverride then flags | Artifact else flags,
         info = toJavaVarArgs(ddef.symbol.info)
       ).enteredAfter(thisPhase).asTerm
 
     val bridgeDef = polyDefDef(bridge, trefs => vrefss => {
-      val (vrefs :+ varArgRef) :: vrefss1 = vrefss
+      val init :+ (last :+ vararg) = vrefss
       // Can't call `.argTypes` here because the underlying array type is of the
       // form `Array[? <: SomeType]`, so we need `.argInfos` to get the `TypeBounds`.
-      val elemtp = varArgRef.tpe.widen.argInfos.head
+      val elemtp = vararg.tpe.widen.argInfos.head
       ref(original.termRef)
         .appliedToTypes(trefs)
-        .appliedToArgs(vrefs :+ tpd.wrapArray(varArgRef, elemtp))
-        .appliedToArgss(vrefss1)
+        .appliedToArgss(init)
+        .appliedToArgs(last :+ tpd.wrapArray(vararg, elemtp))
     })
 
-    Thicket(ddef, bridgeDef)
+    val bridgeDenot = bridge.denot
+    currentClass.info.member(bridge.name).alternatives.find { s =>
+      s.matches(bridgeDenot) &&
+      !(s.asSymDenotation.is(JavaDefined) && javaOverride)
+    } match
+      case Some(conflict) =>
+        ctx.error(s"@varargs produces a forwarder method that conflicts with ${conflict.showDcl}", ddef.sourcePos)
+        EmptyTree
+      case None =>
+        Thicket(ddef, bridgeDef)
 
   /** Convert type from Scala to Java varargs method */
   private def toJavaVarArgs(tp: Type)(using Context): Type = tp match
       case tp: PolyType =>
         tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(tp.resultType))
       case tp: MethodType =>
-        val inits :+ last = tp.paramInfos
-        val vararg = varargArrayType(last)
-        val params = inits :+ vararg
-        tp.derivedLambdaType(tp.paramNames, params, tp.resultType)
+        tp.resultType match
+          case m: MethodType => // multiple param lists
+            tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(m))
+          case _ =>
+            val init :+ last = tp.paramInfos
+            val vararg = varargArrayType(last)
+            tp.derivedLambdaType(tp.paramNames, init :+ vararg, tp.resultType)
 
   /** Translate a repeated type T* to an `Array[? <: Upper]`
    *  such that it is compatible with java varargs.
diff --git a/tests/neg/varargs-annot.scala b/tests/neg/varargs-annot.scala
new file mode 100644
index 000000000000..04352263ad52
--- /dev/null
+++ b/tests/neg/varargs-annot.scala
@@ -0,0 +1,27 @@
+import annotation.varargs
+
+// Failing varargs annotation
+object Test {
+
+  trait A {
+    def v1(a: Int, b: Array[String]) = a
+  }
+
+  trait B extends A { // error (could we get rid of that one?)
+    @varargs def v1(a: Int, b: String*) = a + b.length // error
+  }
+
+  @varargs def nov(a: Int) = 0 // error: A method without repeated parameters cannot be annotated with @varargs
+  @varargs def v(a: Int, b: String*) = a + b.length // ok
+
+  @varargs def v2(a: Int, b: String*) = 0 // error
+  def v2(a: Int, b: Array[String]) = 0
+
+  @varargs def v3(a: String*)(b: Int) = b + a.length // error
+  @varargs def v4(a: String)(b: Int) = b + a.length // error
+  @varargs def v5(a: String)(b: Int*) = a + b.sum // ok
+
+  @varargs def v6: Int = 1 // error
+  @varargs def v7(i: Int*)() = i.sum // error
+
+}
diff --git a/tests/run/varargs-abstract/Test.java b/tests/run/varargs-abstract/Test.java
index 31dfcedc07a7..de19a7d23d57 100644
--- a/tests/run/varargs-abstract/Test.java
+++ b/tests/run/varargs-abstract/Test.java
@@ -8,7 +8,7 @@ public static void main(String[] args) {
     c.y("a", "b", "c");
     c.z("a", "b", "c");
 
-    VarargAbstractClass i = new ClassImplementsClass();
+    VarargAbstractClass<String> i = new ClassImplementsClass();
 
     i.x("a", "b", "c");
     i.y("a", "b", "c");

From 5cb324d73b3ad4922661825fa4704521d2675b1c Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Fri, 3 Jul 2020 02:35:45 +0200
Subject: [PATCH 04/12] Validate PolyType for `@varargs`

---
 compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index 5e73b68a8ef7..9c188b60bb30 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -147,13 +147,15 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   /** Is this the type of a method that has a repeated parameter type as
    *  its last parameter in the last parameter list?
    */
-  private def isValidJavaVarArgs(t: Type)(using Context): Boolean = t match
+  private def isValidJavaVarArgs(tp: Type)(using Context): Boolean = tp match
     case mt: MethodType =>
       val initp :+ lastp = mt.paramInfoss
       initp.forall(_.forall(!_.isRepeatedParam)) &&
       lastp.nonEmpty &&
       lastp.init.forall(!_.isRepeatedParam) &&
       lastp.last.isRepeatedParam
+    case pt: PolyType =>
+      isValidJavaVarArgs(pt.resultType)
     case _ => false
 
 

From b527a75dd8443472fbef8e156f41bace1b590455 Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Wed, 8 Jul 2020 23:50:06 +0200
Subject: [PATCH 05/12] Fix "types differ" error

---
 .../tools/dotc/transform/ElimRepeated.scala   | 26 +++++++++++--------
 tests/neg/varargs-annot.scala                 |  2 +-
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index 9c188b60bb30..be4246c0c693 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -185,17 +185,6 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
         info = toJavaVarArgs(ddef.symbol.info)
       ).enteredAfter(thisPhase).asTerm
 
-    val bridgeDef = polyDefDef(bridge, trefs => vrefss => {
-      val init :+ (last :+ vararg) = vrefss
-      // Can't call `.argTypes` here because the underlying array type is of the
-      // form `Array[? <: SomeType]`, so we need `.argInfos` to get the `TypeBounds`.
-      val elemtp = vararg.tpe.widen.argInfos.head
-      ref(original.termRef)
-        .appliedToTypes(trefs)
-        .appliedToArgss(init)
-        .appliedToArgs(last :+ tpd.wrapArray(vararg, elemtp))
-    })
-
     val bridgeDenot = bridge.denot
     currentClass.info.member(bridge.name).alternatives.find { s =>
       s.matches(bridgeDenot) &&
@@ -205,6 +194,21 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
         ctx.error(s"@varargs produces a forwarder method that conflicts with ${conflict.showDcl}", ddef.sourcePos)
         EmptyTree
       case None =>
+        val bridgeDef = polyDefDef(bridge, trefs => vrefss => {
+          val init :+ (last :+ vararg) = vrefss
+          // Can't call `.argTypes` here because the underlying array type is of the
+          // form `Array[? <: SomeType]`, so we need `.argInfos` to get the `TypeBounds`.
+          val elemtp = vararg.tpe.widen.argInfos.head
+
+          // The generation of the forwarding call needs to be deferred, otherwise
+          // generic and curried methods won't pass the tree checker.
+          atNextPhase {
+            ref(original.termRef)
+              .appliedToTypes(trefs)
+              .appliedToArgss(init)
+              .appliedToArgs(last :+ tpd.wrapArray(vararg, elemtp))
+            }
+          })
         Thicket(ddef, bridgeDef)
 
   /** Convert type from Scala to Java varargs method */
diff --git a/tests/neg/varargs-annot.scala b/tests/neg/varargs-annot.scala
index 04352263ad52..f5629e7ae027 100644
--- a/tests/neg/varargs-annot.scala
+++ b/tests/neg/varargs-annot.scala
@@ -7,7 +7,7 @@ object Test {
     def v1(a: Int, b: Array[String]) = a
   }
 
-  trait B extends A { // error (could we get rid of that one?)
+  trait B extends A {
     @varargs def v1(a: Int, b: String*) = a + b.length // error
   }
 

From 3ae6cc4351606e47241440f51a9659f5769c8326 Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Thu, 9 Jul 2020 21:00:07 +0200
Subject: [PATCH 06/12] Fix generic signature of java-compatible varargs

---
 .../src/dotty/tools/dotc/transform/ElimRepeated.scala | 11 +++++------
 .../tools/dotc/transform/GenericSignatures.scala      |  7 ++++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index be4246c0c693..af34256d9c87 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -227,15 +227,14 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   /** Translate a repeated type T* to an `Array[? <: Upper]`
    *  such that it is compatible with java varargs.
    *
-   *  If T is not a primitive type, we set `Upper = T & AnyRef`
+   *  When necessary we set `Upper = T & AnyRef`
    *  to prevent the erasure of `Array[? <: Upper]` to Object,
    *  which would break the varargs from Java.
    */
   private def varargArrayType(tp: Type)(using Context): Type =
-    val array = tp.translateFromRepeated(toArray = true)
-    val element = array.elemType.typeSymbol
-
-    if element.isPrimitiveValueClass then array
-    else defn.ArrayOf(TypeBounds.upper(AndType(element.typeRef, defn.AnyRefType)))
+    val array = tp.translateFromRepeated(toArray = true) // Array[? <: T]
+    val element = array.elemType.hiBound // T
 
+    if element <:< defn.AnyRefType || element.typeSymbol.isPrimitiveValueClass then array
+    else defn.ArrayOf(TypeBounds.upper(AndType(element, defn.AnyRefType))) // Array[? <: T & AnyRef]
 }
diff --git a/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala b/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
index e2d6362ce1ff..515f2660d85b 100644
--- a/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
+++ b/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
@@ -186,10 +186,11 @@ object GenericSignatures {
         case defn.ArrayOf(elemtp) =>
           if (isUnboundedGeneric(elemtp))
             jsig(defn.ObjectType)
-          else {
+          else
             builder.append(ClassfileConstants.ARRAY_TAG)
-            jsig(elemtp)
-          }
+            elemtp match
+              case TypeBounds(lo, hi) => jsig(hi.widenDealias)
+              case _ => jsig(elemtp)
 
         case RefOrAppliedType(sym, pre, args) =>
           if (sym == defn.PairClass && tp.tupleArity > Definitions.MaxTupleArity)

From cced03713b98f5100b01f854c16f536b93275ad4 Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Thu, 9 Jul 2020 21:13:25 +0200
Subject: [PATCH 07/12] Improve `@varargs` errors and fix some doc

---
 .../tools/dotc/transform/ElimRepeated.scala   | 42 ++++++++++---------
 .../dotc/transform/GenericSignatures.scala    |  4 +-
 2 files changed, 24 insertions(+), 22 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index af34256d9c87..e36f315c169c 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -128,7 +128,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
                       |  - there must be a single repeated parameter
                       |  - it must be the last argument in the last parameter list
                       |""".stripMargin,
-              tree.sourcePos)
+              sym.sourcePos)
             tree
           else
             addVarArgsBridge(tree, isOverride)
@@ -136,7 +136,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
           tree
       else
         if hasAnnotation then
-          ctx.error("A method without repeated parameters cannot be annotated with @varargs", tree.sourcePos)
+          ctx.error("A method without repeated parameters cannot be annotated with @varargs", sym.sourcePos)
         tree
     }
 
@@ -156,7 +156,8 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
       lastp.last.isRepeatedParam
     case pt: PolyType =>
       isValidJavaVarArgs(pt.resultType)
-    case _ => false
+    case _ =>
+      throw new Exception("Match error in @varargs bridge logic. This should not happen, please open an issue " + tp)
 
 
   /** Add a Java varargs bridge
@@ -179,22 +180,23 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     // although it's not strictly necessary for overrides
     // (but it is for non-overrides)
     val flags = ddef.symbol.flags | JavaVarargs
+
+    // The java-compatible bridge symbol
     val bridge = original.copy(
         // non-overrides cannot be synthetic otherwise javac refuses to call them
         flags = if javaOverride then flags | Artifact else flags,
         info = toJavaVarArgs(ddef.symbol.info)
-      ).enteredAfter(thisPhase).asTerm
+      ).asTerm
 
-    val bridgeDenot = bridge.denot
     currentClass.info.member(bridge.name).alternatives.find { s =>
-      s.matches(bridgeDenot) &&
-      !(s.asSymDenotation.is(JavaDefined) && javaOverride)
+      s.matches(bridge) &&
+      !(javaOverride && s.asSymDenotation.is(JavaDefined))
     } match
       case Some(conflict) =>
-        ctx.error(s"@varargs produces a forwarder method that conflicts with ${conflict.showDcl}", ddef.sourcePos)
-        EmptyTree
+        ctx.error(s"@varargs produces a forwarder method that conflicts with ${conflict.showDcl}", original.sourcePos)
+        ddef
       case None =>
-        val bridgeDef = polyDefDef(bridge, trefs => vrefss => {
+        val bridgeDef = polyDefDef(bridge.enteredAfter(thisPhase), trefs => vrefss => {
           val init :+ (last :+ vararg) = vrefss
           // Can't call `.argTypes` here because the underlying array type is of the
           // form `Array[? <: SomeType]`, so we need `.argInfos` to get the `TypeBounds`.
@@ -213,16 +215,16 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
 
   /** Convert type from Scala to Java varargs method */
   private def toJavaVarArgs(tp: Type)(using Context): Type = tp match
-      case tp: PolyType =>
-        tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(tp.resultType))
-      case tp: MethodType =>
-        tp.resultType match
-          case m: MethodType => // multiple param lists
-            tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(m))
-          case _ =>
-            val init :+ last = tp.paramInfos
-            val vararg = varargArrayType(last)
-            tp.derivedLambdaType(tp.paramNames, init :+ vararg, tp.resultType)
+    case tp: PolyType =>
+      tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(tp.resultType))
+    case tp: MethodType =>
+      tp.resultType match
+        case m: MethodType => // multiple param lists
+          tp.derivedLambdaType(tp.paramNames, tp.paramInfos, toJavaVarArgs(m))
+        case _ =>
+          val init :+ last = tp.paramInfos
+          val vararg = varargArrayType(last)
+          tp.derivedLambdaType(tp.paramNames, init :+ vararg, tp.resultType)
 
   /** Translate a repeated type T* to an `Array[? <: Upper]`
    *  such that it is compatible with java varargs.
diff --git a/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala b/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
index 515f2660d85b..5b2592b5009b 100644
--- a/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
+++ b/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
@@ -314,8 +314,8 @@ object GenericSignatures {
     *  - If the list contains one or more occurrences of scala.Array with
     *    type parameters El1, El2, ... then the dominator is scala.Array with
     *    type parameter of intersectionDominator(List(El1, El2, ...)).           <--- @PP: not yet in spec.
-    *  - Otherwise, the list is reduced to a subsequence containing only types
-    *    which are not subtypes of other listed types (the span.)
+    *  - Otherwise, the list is reduced to a subsequence containing only the
+    *    types that are not supertypes of other listed types (the span.)
     *  - If the span is empty, the dominator is Object.
     *  - If the span contains a class Tc which is not a trait and which is
     *    not Object, the dominator is Tc.                                        <--- @PP: "which is not Object" not in spec.

From 5c007b03cb6d7a52bf735daabf48dba5c7f25355 Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Thu, 9 Jul 2020 21:14:45 +0200
Subject: [PATCH 08/12] Add more varargs tests

---
 tests/pos/varargs-annot-currying.scala | 18 ++++++++++++++++
 tests/pos/varargs-annot-generics.scala | 21 +++++++++++++++++++
 tests/run/varargs-abstract/Test.java   | 20 +++++++++++-------
 tests/run/varargs-abstract/test.scala  | 29 +++++++++++++++++++-------
 tests/untried/neg/varargs.check        | 10 ---------
 tests/untried/neg/varargs.scala        | 27 ------------------------
 6 files changed, 74 insertions(+), 51 deletions(-)
 create mode 100644 tests/pos/varargs-annot-currying.scala
 create mode 100644 tests/pos/varargs-annot-generics.scala
 delete mode 100644 tests/untried/neg/varargs.check
 delete mode 100644 tests/untried/neg/varargs.scala

diff --git a/tests/pos/varargs-annot-currying.scala b/tests/pos/varargs-annot-currying.scala
new file mode 100644
index 000000000000..f34e4f2190a9
--- /dev/null
+++ b/tests/pos/varargs-annot-currying.scala
@@ -0,0 +1,18 @@
+import scala.annotation.varargs
+
+object VarArgs {
+   @varargs
+   def two(a: Int)(b: String*): Nothing = ???
+
+   @varargs
+   def twoPrimitive(a: Int)(b: Int*): Nothing = ???
+
+   @varargs
+   def three(a3: Int)(b3: String)(c3: String*): Nothing = ???
+
+   @varargs
+   def threePrimitive(a3: Int)(b3: String)(c3: Int*): Nothing = ???
+
+   @varargs
+   def emptyOk()()(xs: String*): Nothing = ???
+}
diff --git a/tests/pos/varargs-annot-generics.scala b/tests/pos/varargs-annot-generics.scala
new file mode 100644
index 000000000000..d3e0ee49ea2f
--- /dev/null
+++ b/tests/pos/varargs-annot-generics.scala
@@ -0,0 +1,21 @@
+import scala.annotation.varargs
+
+object VarArgs {
+   @varargs
+   def foo1[A](x: A, xs: String*): A = ???
+
+   @varargs
+   def foo2[A](x: List[A], xs: String*): A = ???
+
+   @varargs
+   def foo3[A](n: Int*): Unit = ???
+
+   @varargs
+   def bar1[A](x: A*): Unit = ???
+
+   @varargs
+   def bar2[A](x: A, xs: A*): A = ???
+
+   @varargs
+   def bar3[A <: Comparable[A]](xs: A*): A = ???
+}
diff --git a/tests/run/varargs-abstract/Test.java b/tests/run/varargs-abstract/Test.java
index de19a7d23d57..3233d2412894 100644
--- a/tests/run/varargs-abstract/Test.java
+++ b/tests/run/varargs-abstract/Test.java
@@ -2,18 +2,24 @@
 
 public class Test {
   public static void main(String[] args) {
-    ClassImplementsClass c = new ClassImplementsClass();
+    VarargImplClass c = new VarargImplClass();
 
-    c.x("a", "b", "c");
+    c.x(0, 1, 2);
     c.y("a", "b", "c");
     c.z("a", "b", "c");
+    c.generic("a", "b", "c");
+    c.genericBounded("a", "b", "c");
 
-    VarargAbstractClass<String> i = new ClassImplementsClass();
+    VarargAbstractClass<String> i = new VarargImplClass();
 
-    i.x("a", "b", "c");
+    i.x(0, 1, 2);
     i.y("a", "b", "c");
-    // i.z("a", "b", "c");
-    // ClassCastException at runtime because the generated
-    // signature of z doesn't mention the type parameter (it should)
+    i.z("a", "b", "c");
+    i.generic("a", "b", "c");
+    i.genericBounded("a", "b", "c");
+
+    VarargClassBounded<String> b = new VarargClassBounded<>();
+    b.v1("a", "b", "c");
+    b.v2("a", "b", "c");
   }
 }
diff --git a/tests/run/varargs-abstract/test.scala b/tests/run/varargs-abstract/test.scala
index 073f8d086f28..2edb43c4cf50 100644
--- a/tests/run/varargs-abstract/test.scala
+++ b/tests/run/varargs-abstract/test.scala
@@ -2,17 +2,32 @@ import scala.annotation.varargs
 
 abstract class VarargAbstractClass[T] {
   @varargs
-  def x(els: String*): Int
+  def x(v: Int*): Int
 
   @varargs
-  def y(els: String*): Int
+  def y(v: String*): Int
 
   @varargs
-  def z(els: T*): Int
+  def z(v: T*): Int
+
+  @varargs
+  def generic[E](e: E*): Unit = ()
+
+  @varargs
+  def genericBounded[E <: Comparable[E] & Serializable](e: E*): Unit = ()
+}
+
+class VarargImplClass extends VarargAbstractClass[String] {
+
+  override def x(v: Int*): Int = v.length
+  override def y(v: String*): Int = v.length
+  override def z(v: String*): Int = v.length
 }
-class ClassImplementsClass extends VarargAbstractClass[String] {
 
-  override def x(els: String*): Int = els.length
-  override def y(els: String*): Int = els.length
-  override def z(els: String*): Int = els.length
+class VarargClassBounded[B <: Comparable[B]] {
+  @varargs
+  def v1(v: B*): Unit = ()
+
+  @varargs
+  def v2(first: B, more: B*): B = first
 }
diff --git a/tests/untried/neg/varargs.check b/tests/untried/neg/varargs.check
deleted file mode 100644
index 5f002fdae4a9..000000000000
--- a/tests/untried/neg/varargs.check
+++ /dev/null
@@ -1,10 +0,0 @@
-varargs.scala:16: error: A method with a varargs annotation produces a forwarder method with the same signature (a: Int, b: Array[String])Int as an existing method.
-    @varargs def v1(a: Int, b: String*) = a + b.length
-                 ^
-varargs.scala:19: error: A method without repeated parameters cannot be annotated with the `varargs` annotation.
-  @varargs def nov(a: Int) = 0
-               ^
-varargs.scala:21: error: A method with a varargs annotation produces a forwarder method with the same signature (a: Int, b: Array[String])Int as an existing method.
-  @varargs def v2(a: Int, b: String*) = 0
-               ^
-3 errors found
diff --git a/tests/untried/neg/varargs.scala b/tests/untried/neg/varargs.scala
deleted file mode 100644
index ce7f0d71fee8..000000000000
--- a/tests/untried/neg/varargs.scala
+++ /dev/null
@@ -1,27 +0,0 @@
-
-
-
-import annotation.varargs
-
-
-
-// Failing varargs annotation
-object Test {
-
-  trait A {
-    def v1(a: Int, b: Array[String]) = a
-  }
-
-  trait B extends A {
-    @varargs def v1(a: Int, b: String*) = a + b.length
-  }
-
-  @varargs def nov(a: Int) = 0
-  @varargs def v(a: Int, b: String*) = a + b.length
-  @varargs def v2(a: Int, b: String*) = 0
-  def v2(a: Int, b: Array[String]) = 0
-
-  def main(args: Array[String]): Unit = {
-  }
-
-}

From 06c0ef7572fb1022f71796a2752495d1933767ea Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Fri, 10 Jul 2020 10:55:43 +0200
Subject: [PATCH 09/12] Update sconfig submodule

---
 .gitmodules                                | 2 +-
 community-build/community-projects/sconfig | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.gitmodules b/.gitmodules
index 6cf9427b78b5..99cfc8fe442d 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -67,7 +67,7 @@
 	url = https://github.com/dotty-staging/upickle.git
 [submodule "community-build/community-projects/sconfig"]
 	path = community-build/community-projects/sconfig
-	url = https://github.com/ekrich/sconfig.git
+	url = https://github.com/dotty-staging/sconfig.git
 [submodule "community-build/community-projects/zio"]
 	path = community-build/community-projects/zio
 	url = https://github.com/dotty-staging/zio.git
diff --git a/community-build/community-projects/sconfig b/community-build/community-projects/sconfig
index a1579a935f79..38d620bdab66 160000
--- a/community-build/community-projects/sconfig
+++ b/community-build/community-projects/sconfig
@@ -1 +1 @@
-Subproject commit a1579a935f79d34c66a813f0cf71a674c092179b
+Subproject commit 38d620bdab6656850ab0358583d2bb3638f83150

From b828c69194a1d68b7de7594f541a9c070164cf8c Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Sat, 11 Jul 2020 19:31:18 +0200
Subject: [PATCH 10/12] Replace "bridge" by more correct "forwarder"

---
 .../tools/dotc/transform/ElimRepeated.scala   | 40 +++++++++----------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index e36f315c169c..c53b5fdd6119 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -28,7 +28,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
 
   override def phaseName: String = ElimRepeated.name
 
-  override def changesMembers: Boolean = true // the phase adds vararg bridges
+  override def changesMembers: Boolean = true // the phase adds vararg forwarders
 
   def transformInfo(tp: Type, sym: Symbol)(using Context): Type =
     elimRepeated(tp)
@@ -37,7 +37,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     super.transform(ref) match
       case ref1: SymDenotation if (ref1 ne ref) && overridesJava(ref1.symbol) =>
         // This method won't override the corresponding Java method at the end of this phase,
-        // only the bridge added by `addVarArgsBridge` will.
+        // only the forwarder added by `addVarArgsForwarder` will.
         ref1.copySymDenotation(initFlags = ref1.flags &~ Override)
       case ref1 =>
         ref1
@@ -131,7 +131,7 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
               sym.sourcePos)
             tree
           else
-            addVarArgsBridge(tree, isOverride)
+            addVarArgsForwarder(tree, isOverride)
         else
           tree
       else
@@ -157,46 +157,46 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     case pt: PolyType =>
       isValidJavaVarArgs(pt.resultType)
     case _ =>
-      throw new Exception("Match error in @varargs bridge logic. This should not happen, please open an issue " + tp)
+      throw new Exception("Match error in @varargs checks. This should not happen, please open an issue " + tp)
 
 
-  /** Add a Java varargs bridge
-   *  @param ddef    the original method definition
-   *  @param addFlag the flag to add to the method symbol
-
-   *  @return a thicket consisting of `ddef` and a varargs bridge method
-   *          which forwards java varargs to `ddef`. It retains all the
+  /** Add a Java varargs forwarder
+   *  @param ddef     the original method definition
+   *  @param isBridge true if we are generating a "bridge" (synthetic override forwarder)
+   *
+   *  @return a thicket consisting of `ddef` and an additional method
+   *          that forwards java varargs to `ddef`. It retains all the
    *          flags of `ddef` except `Private`.
    *
-   *  A bridge is necessary because the following hold:
+   *  A forwarder is necessary because the following hold:
    *    - the varargs in `ddef` will change from `RepeatedParam[T]` to `Seq[T]` after this phase
    *    - _but_ the callers of `ddef` expect its varargs to be changed to `Array[? <: T]`
-   *  The solution is to add a "bridge" method that converts its argument from `Array[? <: T]` to `Seq[T]` and
+   *  The solution is to add a method that converts its argument from `Array[? <: T]` to `Seq[T]` and
    *  forwards it to `ddef`.
    */
-  private def addVarArgsBridge(ddef: DefDef, javaOverride: Boolean)(using ctx: Context): Tree =
+  private def addVarArgsForwarder(ddef: DefDef, isBridge: Boolean)(using ctx: Context): Tree =
     val original = ddef.symbol.asTerm
     // For simplicity we always set the varargs flag
     // although it's not strictly necessary for overrides
     // (but it is for non-overrides)
     val flags = ddef.symbol.flags | JavaVarargs
 
-    // The java-compatible bridge symbol
-    val bridge = original.copy(
+    // The java-compatible forwarder symbol
+    val sym = original.copy(
         // non-overrides cannot be synthetic otherwise javac refuses to call them
-        flags = if javaOverride then flags | Artifact else flags,
+        flags = if isBridge then flags | Artifact else flags,
         info = toJavaVarArgs(ddef.symbol.info)
       ).asTerm
 
-    currentClass.info.member(bridge.name).alternatives.find { s =>
-      s.matches(bridge) &&
-      !(javaOverride && s.asSymDenotation.is(JavaDefined))
+    currentClass.info.member(sym.name).alternatives.find { s =>
+      s.matches(sym) &&
+      !(isBridge && s.asSymDenotation.is(JavaDefined))
     } match
       case Some(conflict) =>
         ctx.error(s"@varargs produces a forwarder method that conflicts with ${conflict.showDcl}", original.sourcePos)
         ddef
       case None =>
-        val bridgeDef = polyDefDef(bridge.enteredAfter(thisPhase), trefs => vrefss => {
+        val bridgeDef = polyDefDef(sym.enteredAfter(thisPhase), trefs => vrefss => {
           val init :+ (last :+ vararg) = vrefss
           // Can't call `.argTypes` here because the underlying array type is of the
           // form `Array[? <: SomeType]`, so we need `.argInfos` to get the `TypeBounds`.

From 20754c2d7e223a76eb0d12ea8728a1a8cfa90cbe Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Sun, 12 Jul 2020 00:13:59 +0200
Subject: [PATCH 11/12] Remove atNextPhase and use atPhase only where necessary

---
 .../tools/dotc/transform/ElimRepeated.scala   | 88 ++++++++++---------
 1 file changed, 47 insertions(+), 41 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
index c53b5fdd6119..c2effb6fc7b0 100644
--- a/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala
@@ -115,30 +115,34 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
    *  Also transform trees inside method annotation.
    */
   override def transformDefDef(tree: DefDef)(using Context): Tree =
-    atPhase(thisPhase) {
-      val sym = tree.symbol
-      val hasAnnotation = hasVarargsAnnotation(sym)
-      if hasRepeatedParams(sym) then
-        val isOverride = overridesJava(sym)
-        if isOverride || hasAnnotation || parentHasAnnotation(sym) then
-          // java varargs are more restrictive than scala's
-          // see https://github.com/scala/bug/issues/11714
-          if !isValidJavaVarArgs(sym.info) then
-            ctx.error("""To generate java-compatible varargs:
-                      |  - there must be a single repeated parameter
-                      |  - it must be the last argument in the last parameter list
-                      |""".stripMargin,
-              sym.sourcePos)
-            tree
-          else
-            addVarArgsForwarder(tree, isOverride)
-        else
+    val sym = tree.symbol
+    val hasAnnotation = hasVarargsAnnotation(sym)
+
+    // atPhase(thisPhase) is used where necessary to see the repeated
+    // parameters before their elimination
+    val hasRepeatedParam = atPhase(thisPhase)(hasRepeatedParams(sym))
+    if hasRepeatedParam then
+      val isOverride = atPhase(thisPhase)(overridesJava(sym))
+      if isOverride || hasAnnotation || parentHasAnnotation(sym) then
+        // java varargs are more restrictive than scala's
+        // see https://github.com/scala/bug/issues/11714
+        val validJava = atPhase(thisPhase)(isValidJavaVarArgs(sym.info))
+        if !validJava then
+          ctx.error("""To generate java-compatible varargs:
+                    |  - there must be a single repeated parameter
+                    |  - it must be the last argument in the last parameter list
+                    |""".stripMargin,
+            sym.sourcePos)
           tree
+        else
+          // non-overrides cannot be synthetic otherwise javac refuses to call them
+          addVarArgsForwarder(tree, isBridge = isOverride)
       else
-        if hasAnnotation then
-          ctx.error("A method without repeated parameters cannot be annotated with @varargs", sym.sourcePos)
         tree
-    }
+    else
+      if hasAnnotation then
+        ctx.error("A method without repeated parameters cannot be annotated with @varargs", sym.sourcePos)
+      tree
 
   /** Is there a repeated parameter in some parameter list? */
   private def hasRepeatedParams(sym: Symbol)(using Context): Boolean =
@@ -175,23 +179,30 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
    *  forwards it to `ddef`.
    */
   private def addVarArgsForwarder(ddef: DefDef, isBridge: Boolean)(using ctx: Context): Tree =
-    val original = ddef.symbol.asTerm
-    // For simplicity we always set the varargs flag
-    // although it's not strictly necessary for overrides
-    // (but it is for non-overrides)
-    val flags = ddef.symbol.flags | JavaVarargs
+    val original = ddef.symbol
 
     // The java-compatible forwarder symbol
-    val sym = original.copy(
-        // non-overrides cannot be synthetic otherwise javac refuses to call them
+    val sym = atPhase(thisPhase) {
+      // Capture the flags before they get modified by #transform.
+      // For simplicity we always set the varargs flag,
+      // although it's not strictly necessary for overrides.
+      val flags = original.flags | JavaVarargs
+      original.copy(
         flags = if isBridge then flags | Artifact else flags,
         info = toJavaVarArgs(ddef.symbol.info)
       ).asTerm
+    }
 
-    currentClass.info.member(sym.name).alternatives.find { s =>
-      s.matches(sym) &&
-      !(isBridge && s.asSymDenotation.is(JavaDefined))
-    } match
+    // Find a method that would conflict with the forwarder if the latter existed.
+    // This needs to be done at thisPhase so that parent @varargs don't conflict.
+    val conflict = atPhase(thisPhase) {
+      currentClass.info.member(sym.name).alternatives.find { s =>
+        s.matches(sym) &&
+        !(isBridge && s.asSymDenotation.is(JavaDefined))
+      }
+    }
+
+    conflict match
       case Some(conflict) =>
         ctx.error(s"@varargs produces a forwarder method that conflicts with ${conflict.showDcl}", original.sourcePos)
         ddef
@@ -201,15 +212,10 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
           // Can't call `.argTypes` here because the underlying array type is of the
           // form `Array[? <: SomeType]`, so we need `.argInfos` to get the `TypeBounds`.
           val elemtp = vararg.tpe.widen.argInfos.head
-
-          // The generation of the forwarding call needs to be deferred, otherwise
-          // generic and curried methods won't pass the tree checker.
-          atNextPhase {
-            ref(original.termRef)
-              .appliedToTypes(trefs)
-              .appliedToArgss(init)
-              .appliedToArgs(last :+ tpd.wrapArray(vararg, elemtp))
-            }
+          ref(original.termRef)
+            .appliedToTypes(trefs)
+            .appliedToArgss(init)
+            .appliedToArgs(last :+ tpd.wrapArray(vararg, elemtp))
           })
         Thicket(ddef, bridgeDef)
 

From d8100b272e2f6a7d449f2c221915de2ecad4b2d6 Mon Sep 17 00:00:00 2001
From: Guillaume Raffin <theelectronwill@gmail.com>
Date: Sun, 12 Jul 2020 00:16:49 +0200
Subject: [PATCH 12/12] Add more varargs tests (again)

---
 tests/neg/varargs-annot.scala                 |  1 +
 tests/run/vararg-extend-java/Vararg.java      |  3 ++
 .../vararg-extend-java/VarargAbstract.java    |  4 +++
 tests/run/vararg-extend-java/test.scala       | 28 +++++++++++++++++++
 4 files changed, 36 insertions(+)
 create mode 100644 tests/run/vararg-extend-java/Vararg.java
 create mode 100644 tests/run/vararg-extend-java/VarargAbstract.java
 create mode 100644 tests/run/vararg-extend-java/test.scala

diff --git a/tests/neg/varargs-annot.scala b/tests/neg/varargs-annot.scala
index f5629e7ae027..085c211e4081 100644
--- a/tests/neg/varargs-annot.scala
+++ b/tests/neg/varargs-annot.scala
@@ -13,6 +13,7 @@ object Test {
 
   @varargs def nov(a: Int) = 0 // error: A method without repeated parameters cannot be annotated with @varargs
   @varargs def v(a: Int, b: String*) = a + b.length // ok
+  def v(a: Int, b: String) = a // ok
 
   @varargs def v2(a: Int, b: String*) = 0 // error
   def v2(a: Int, b: Array[String]) = 0
diff --git a/tests/run/vararg-extend-java/Vararg.java b/tests/run/vararg-extend-java/Vararg.java
new file mode 100644
index 000000000000..c3f286640b7b
--- /dev/null
+++ b/tests/run/vararg-extend-java/Vararg.java
@@ -0,0 +1,3 @@
+public class Vararg {
+  void v(int... i) {}
+}
diff --git a/tests/run/vararg-extend-java/VarargAbstract.java b/tests/run/vararg-extend-java/VarargAbstract.java
new file mode 100644
index 000000000000..be9565f3eaef
--- /dev/null
+++ b/tests/run/vararg-extend-java/VarargAbstract.java
@@ -0,0 +1,4 @@
+public abstract class VarargAbstract {
+  public abstract void v1(String... s);
+  public abstract void v2(String... s);
+}
diff --git a/tests/run/vararg-extend-java/test.scala b/tests/run/vararg-extend-java/test.scala
new file mode 100644
index 000000000000..39e3c632124c
--- /dev/null
+++ b/tests/run/vararg-extend-java/test.scala
@@ -0,0 +1,28 @@
+import scala.annotation.varargs
+
+class VarargImpl extends VarargAbstract {
+  def v1(s: String*) = ()
+
+  override def v2(s: String*) = ()
+}
+
+class VarargSub extends Vararg {
+  override def v(i: Int*) = ()
+}
+
+object Test {
+  def main(args: Array[String]): Unit =
+    val a: VarargAbstract = VarargImpl()
+    a.v1("a", "b", "c")
+    a.v2("a", "b", "c")
+
+    val i: VarargImpl = VarargImpl()
+    i.v1("a", "b", "c")
+    i.v2("a", "b", "c")
+
+    val b: Vararg = VarargSub()
+    b.v(1, 2, 3)
+
+    val c: VarargSub = VarargSub()
+    c.v(1, 2, 3)
+}