Use toVector` for XML literal sequences

In `<a><b/><c/><a>`, a `NodeBuffer` (which extends `ArrayBuffer`) is used to accumulate the children. The buffer is passed to `new Elem($buf: _*)`, which only works thanks to the implicit `collection.Seq[Node] => NodeSeq` declared in scala-xml. With `-Vprint:typer`: ```scala scala> <a><b/></a> [[syntax trees at end of typer]] // rs$line$1 val res0: scala.xml.Elem ={new _root_.scala.xml.Elem(null, "a", _root_.scala.xml.Null, scala.xml.TopScope, false,{val $buf: scala.xml.NodeBuffer = new _root_.scala.xml.NodeBuffer() $buf.&+({{new _root_.scala.xml.Elem(null, "b", _root_.scala.xml.Null, scala.xml.TopScope, true, [ : scala.xml.Node]*) } } ) scala.xml.NodeSeq.seqToNodeSeq($buf) }* ) } ``` The implicit was not inserted in 2.12 because the varargs parameter of Elem accepted a `collection.Seq`.

Author: lrytz

compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala

@@ -42,12 +42,14 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(using Context){
 val_Group:TypeName="Group"
 val_MetaData:TypeName="MetaData"
 val_NamespaceBinding:TypeName="NamespaceBinding"
+val_Node:TypeName="Node"
 val_NodeBuffer:TypeName="NodeBuffer"
 val_PrefixedAttribute:TypeName="PrefixedAttribute"
 val_ProcInstr:TypeName="ProcInstr"
 val_Text:TypeName="Text"
 val_Unparsed:TypeName="Unparsed"
 val_UnprefixedAttribute:TypeName="UnprefixedAttribute"
+val_Seq:TypeName="Seq"
  }
 
 privateobjectxmltermsextendsScalaTermNames{
@@ -59,12 +61,13 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(using Context){
 val_plus:TermName="&+"
 val_tmpscope:TermName="$tmpscope"
 val_xml:TermName="xml"
+val_toVector:TermName="toVector"
  }
 
-importxmltypes.{_Comment, _Elem, _EntityRef, _Group, _MetaData, _NamespaceBinding, _NodeBuffer,
-_PrefixedAttribute, _ProcInstr, _Text, _Unparsed, _UnprefixedAttribute}
+importxmltypes.{_Comment, _Elem, _EntityRef, _Group, _MetaData, _NamespaceBinding, _NodeBuffer,_Node,
+_PrefixedAttribute, _ProcInstr, _Text, _Unparsed, _UnprefixedAttribute, _Seq}
 
-importxmlterms.{_Null, __Elem, __Text, _buf, _md, _plus, _scope, _tmpscope, _xml}
+importxmlterms.{_Null, __Elem, __Text, _buf, _md, _plus, _scope, _tmpscope, _xml, _toVector}
 
 // convenience methods
 privatedefLL[A](x: A*):List[List[A]] =List(x.toList)
@@ -89,6 +92,7 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(using Context){
 privatedef_scala_xml_UnprefixedAttribute= _scala_xml(_UnprefixedAttribute)
 privatedef_scala_xml__Elem= _scala_xml(__Elem)
 privatedef_scala_xml__Text= _scala_xml(__Text)
+privatedef_scala_Seq_Node=AppliedTypeTree(_scala(_Seq), List(_scala_xml(_Node)))
 
 /** Wildly wrong documentation deleted in favor of "self-documenting code." */
 protecteddefmkXML(
@@ -166,7 +170,7 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(using Context){
 valbuffer=ValDef(_buf, TypeTree(), New(_scala_xml_NodeBuffer, ListOfNil))
 valapplies= args filterNot isEmptyText map (t =>Apply(Select(Ident(_buf), _plus), List(t)))
 
- atSpan(span)(newXMLBlock(buffer :: applies.toList, Ident(_buf)) )
+ atSpan(span)(newXMLBlock(buffer :: applies.toList, Typed(Select(Ident(_buf), _toVector), _scala_Seq_Node)))
  }
 
 /** Returns (Some(prefix) | None, rest) based on position of ':' */

tests/run/xml.scala

@@ -1,12 +1,16 @@
 
 objectTest{
-importscala.xml.NodeBuffer
+importscala.xml._
 
 defmain(args: Array[String]):Unit={
 valxml= <hello>world</hello>
  assert(xml.toString =="helloworld")
-valnodeBuffer:NodeBuffer= <hello/><world/>
- assert(nodeBuffer.mkString =="helloworld")
+valsq:Seq[Node] = <hello/><world/>
+ assert(sq.mkString =="helloworld")
+ assert(sq.isInstanceOf[Vector[_]]) // implementation detail
+
+valsubSq:Node= <a><b/><c/></a>
+ assert(subSq.child.toString =="Vector(b, c)") // implementation detail
  }
 }
 packagescala.xml{