fixup! [core] Add private Layer.layerSeq member function

core/src/main/scala/chisel3/Layer.scala

@@ -161,18 +161,17 @@ object layer {
       case _                 => this.canWriteTo(that.parent)
     }
 
-    /** Return a sequence of this layer and all its parents, excluding the root layer.
+    /** Return a list containg this layer and all its parents, excluding the root
+      * layer.  The deepest layer (this layer) is the first element in the list.
       *
       * @return a sequence of all layers
       */
-    private[chisel3] def layerSeq: Seq[Layer] = {
-      var currentLayer: Layer = this
-      val layers = ArrayBuffer.empty[Layer]
-      while (currentLayer != Layer.Root) {
-        layers.addOne(currentLayer)
-        currentLayer = currentLayer.parent
+    private[chisel3] def layerSeq: List[Layer] = {
+      def rec(current: Layer, acc: List[Layer]): List[Layer] = current match {
+        case Layer.root => acc
+        case _ => rec(current.parent, current :: acc)
       }
-      layers.reverse.toSeq
+      rec(this, Nil)
     }
   }