Fix #8214 Don't consume whitespace after XML

Forward port of scala/scala#4185

Author: som-snytt

Diff for: compiler/src/dotty/tools/dotc/parsing/xml/MarkupParsers.scala

@@ -362,18 +362,18 @@ object MarkupParsers {
         tmppos = Span(curOffset)    // Iuli: added this line, as it seems content_LT uses tmppos when creating trees
         content_LT(ts)
 
-        // parse more XML ?
+        // parse more XML?
         if (charComingAfter(xSpaceOpt()) == '<') {
-          xSpaceOpt()
-          while (ch == '<') {
-            nextch()
-            ts append element
+          while {
             xSpaceOpt()
-          }
+            nextch()
+            ts.append(element)
+            charComingAfter(xSpaceOpt()) == '<'
+          } do ()
           handle.makeXMLseq(Span(start, curOffset, start), ts)
         }
         else {
-          assert(ts.length == 1)
+          assert(ts.length == 1, "Require one tree")
           ts(0)
         }
       },

Diff for: tests/run/xml.scala

@@ -0,0 +1,42 @@
+
+object Test {
+  import scala.xml.NodeBuffer
+
+  def main(args: Array[String]): Unit = {
+    val xml =  <hello>world</hello>
+    assert(xml.toString == "helloworld")
+    val nodeBuffer: NodeBuffer = <hello/><world/>
+    assert(nodeBuffer.mkString == "helloworld")
+  }
+}
+package scala.xml {
+  type MetaData = AnyRef
+
+  trait NamespaceBinding
+  object TopScope extends NamespaceBinding
+  object Null
+  abstract class Node {
+    def label: String
+    def child: Seq[Node]
+    override def toString = label + child.mkString
+  }
+  class Elem(prefix: String, val label: String, attributes1: MetaData, scope: NamespaceBinding, minimizeEmpty: Boolean, val child: Node*) extends Node
+  class NodeBuffer extends Seq[Node] {
+    val nodes = scala.collection.mutable.ArrayBuffer.empty[Node]
+    def &+(o: Any): NodeBuffer =
+      o match {
+        case n: Node => nodes.addOne(n) ; this
+        case t: Text => nodes.addOne(Atom(t)) ; this
+      }
+    // Members declared in scala.collection.IterableOnce
+    def iterator: Iterator[scala.xml.Node] = nodes.iterator
+    // Members declared in scala.collection.SeqOps
+    def apply(i: Int): scala.xml.Node = nodes(i)
+    def length: Int = nodes.length
+  }
+  case class Text(text: String)
+  case class Atom(t: Text) extends Node {
+    def label = t.text
+    def child = Nil
+  }
+}