Fix #4785: change typing rule for _* args

In expression position, if a tree is of the form `expr: _*`, try to type
`expr` as an `Array` and as a `Seq` if there are errors

Author: allanrenucci

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -345,11 +345,6 @@ class Definitions {
     def Predef_classOf(implicit ctx: Context) = Predef_classOfR.symbol
     lazy val Predef_undefinedR = ScalaPredefModule.requiredMethodRef("???")
     def Predef_undefined(implicit ctx: Context) = Predef_undefinedR.symbol
-    // The set of all wrap{X, Ref}Array methods, where X is a value type
-    val Predef_wrapArray = new PerRun[collection.Set[Symbol]]({ implicit ctx =>
-      val methodNames = ScalaValueTypes.map(TreeGen.wrapArrayMethodName) + nme.wrapRefArray
-      methodNames.map(ScalaPredefModule.requiredMethodRef(_).symbol)
-    })
 
   lazy val ScalaRuntimeModuleRef = ctx.requiredModuleRef("scala.runtime.ScalaRunTime")
   def ScalaRuntimeModule(implicit ctx: Context) = ScalaRuntimeModuleRef.symbol

compiler/src/dotty/tools/dotc/core/TypeApplications.scala

@@ -492,7 +492,7 @@ class TypeApplications(val self: Type) extends AnyVal {
   }
 
   /** The element type of a sequence or array */
-  def elemType(implicit ctx: Context): Type = self match {
+  def elemType(implicit ctx: Context): Type = self.widenDealias match {
     case defn.ArrayOf(elemtp) => elemtp
     case JavaArrayType(elemtp) => elemtp
     case _ => self.baseType(defn.SeqClass).argInfos.headOption.getOrElse(NoType)

compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala

@@ -85,9 +85,14 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
     val args1 = tree.args.zipWithConserve(formals) { (arg, formal) =>
       arg match {
         case arg: Typed if isWildcardStarArg(arg) =>
-          if (tree.fun.symbol.is(JavaDefined) && arg.expr.tpe.derivesFrom(defn.SeqClass))
-            seqToArray(arg.expr, formal.underlyingIfRepeated(isJava = true))
-          else arg.expr
+          val isJavaDefined = tree.fun.symbol.is(JavaDefined)
+          val expr = arg.expr
+          if (isJavaDefined && expr.tpe.derivesFrom(defn.SeqClass))
+            seqToArray(expr, formal.underlyingIfRepeated(isJava = true))
+          else if (!isJavaDefined && expr.tpe.derivesFrom(defn.ArrayClass))
+            arrayToSeq(expr)
+          else
+            expr
         case arg => arg
       }
     }
@@ -98,12 +103,10 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
   private def seqToArray(tree: Tree, pt: Type)(implicit ctx: Context): Tree = tree match {
     case SeqLiteral(elems, elemtpt) =>
       JavaSeqLiteral(elems, elemtpt)
-    case app@Apply(fun, args) if defn.Predef_wrapArray().contains(fun.symbol) => // rewrite a call to `wrapXArray(arr)` to `arr`
-      args.head
     case _ =>
       val elemType = tree.tpe.elemType
       var elemClass = elemType.classSymbol
-      if (defn.NotRuntimeClasses contains elemClass) elemClass = defn.ObjectClass
+      if (defn.NotRuntimeClasses.contains(elemClass)) elemClass = defn.ObjectClass
       ref(defn.DottyArraysModule)
         .select(nme.seqToArray)
         .appliedToType(elemType)
@@ -112,6 +115,10 @@ class ElimRepeated extends MiniPhase with InfoTransformer { thisPhase =>
           // Because of phantomclasses, the Java array's type might not conform to the return type
   }
 
+  /** Convert Java array argument to Scala Seq of type `pt` */
+  private def arrayToSeq(tree: Tree)(implicit ctx: Context): Tree =
+    TreeGen.wrapArray(tree, tree.tpe.elemType)
+
   override def transformTypeApply(tree: TypeApply)(implicit ctx: Context): Tree =
     transformTypeOfTree(tree)
 

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -557,11 +557,26 @@ class Typer extends Namer
         else typed(tree.expr, tpt.tpe.widenSkolem)
       assignType(cpy.Typed(tree)(expr1, tpt), underlyingTreeTpe)
     }
-    if (untpd.isWildcardStarArg(tree))
+    if (untpd.isWildcardStarArg(tree)) {
+      /** If tree is of the form `expr: _*`, try to type `expr` as an `Array`
+       *  and as a `Seq` if there are errors.
+       */
+      def typedWildcardStarArgExpr = {
+        def asSeq(implicit ctx: Context) =
+          seqToRepeated(typedExpr(tree.expr, defn.SeqType.appliedTo(defn.AnyType)))
+        def asArray(elemTpe: Type)(implicit ctx: Context) = {
+          val expr = typedExpr(tree.expr, defn.ArrayType.appliedTo(elemTpe))
+          Typed(expr, TypeTree(defn.RepeatedParamType.appliedTo(elemTpe)))
+        }
+        val elemTpe = pt.elemType
+        if (elemTpe.exists) tryAlternatively[Tree](asArray(elemTpe)(_))(asSeq(_))
+        else asSeq
+      }
       cases(
         ifPat = ascription(TypeTree(defn.RepeatedParamType.appliedTo(pt)), isWildcard = true),
-        ifExpr = seqToRepeated(typedExpr(tree.expr, defn.SeqType.appliedTo(defn.AnyType))),
+        ifExpr = typedWildcardStarArgExpr,
         wildName = nme.WILDCARD_STAR)
+    }
     else {
       def typedTpt = checkSimpleKinded(typedType(tree.tpt))
       def handlePattern: Tree = {