Do not ignore XML comments when parsing:

fixes #508

- set `org.xml.sax.ext.LexicalHandler` on the `SAXParser` that `XMLLoader` uses;
- override `LexicalHandler.comment()` in `FactoryAdapter` so that comments are added to the element content;
- add unit tests;
- add excludes for the binary compatibility checks.

Author: dubinsky

build.sbt

@@ -68,6 +68,15 @@ lazy val xml = crossProject(JSPlatform, JVMPlatform, NativePlatform)
         // we compare classes built on JDK 16 (which we only do on CI, not at release time)
         // to previous-version artifacts that were built on 8.  see scala/scala-xml#501
         exclude[DirectMissingMethodProblem]("scala.xml.include.sax.XIncluder.declaration"),
+
+        // caused by the switch from DefaultHandler to DefaultHandler2:
+        exclude[MissingTypesProblem]("scala.xml.parsing.FactoryAdapter"),
+        exclude[MissingTypesProblem]("scala.xml.parsing.NoBindingFactoryAdapter"),
+
+        exclude[DirectMissingMethodProblem]("scala.xml.parsing.FactoryAdapter.comment"),
+        exclude[ReversedMissingMethodProblem]("scala.xml.parsing.FactoryAdapter.createComment"),
+        exclude[DirectMissingMethodProblem]("scala.xml.parsing.FactoryAdapter.createComment"),
+        exclude[DirectMissingMethodProblem]("scala.xml.parsing.NoBindingFactoryAdapter.createComment")
       )
     },
 

jvm/src/test/scala/scala/xml/XMLTest.scala

@@ -6,7 +6,6 @@ import org.junit.{Test => UnitTest}
 import org.junit.Assert.assertTrue
 import org.junit.Assert.assertFalse
 import org.junit.Assert.assertEquals
-import scala.xml.parsing.ConstructingParser
 import java.io.StringWriter
 import java.io.ByteArrayOutputStream
 import java.io.StringReader
@@ -581,6 +580,21 @@ class XMLTestJVM {
     XML.loadString(broken)
   }
 
+  @UnitTest
+  def issue508: Unit = {
+    def check(xml: String): Unit = assertEquals(xml, XML.loadString(xml).toString)
+
+    check("<a><!-- comment --> suffix</a>")
+    check("<a>prefix <!-- comment --> suffix</a>")
+    check("<a>prefix <b><!-- comment --></b> suffix</a>")
+
+    // TODO since XMLLoader retrieves FactoryAdapter.rootNode,
+    // capturing comments before and after the root element is not currently possible
+    // (by the way, the same applies to processing instructions).
+    //check("<!-- prologue --><a>text</a>")
+    //check("<a>text</a><!-- epilogue -->")
+  }
+
   @UnitTest
   def nodeSeqNs: Unit = {
     val x = {
@@ -746,5 +760,4 @@ class XMLTestJVM {
 
     assertEquals("", x.xEntityValue())
   }
-
 }

shared/src/main/scala/scala/xml/factory/NodeFactory.scala

@@ -34,7 +34,7 @@ trait NodeFactory[A <: Node] {
   def eqElements(ch1: Seq[Node], ch2: Seq[Node]): Boolean =
     ch1.view.zipAll(ch2.view, null, null) forall { case (x, y) => x eq y }
 
-  def nodeEquals(n: Node, pre: String, name: String, attrSeq: MetaData, scope: NamespaceBinding, children: Seq[Node]) =
+  def nodeEquals(n: Node, pre: String, name: String, attrSeq: MetaData, scope: NamespaceBinding, children: Seq[Node]): Boolean =
     n.prefix == pre &&
       n.label == name &&
       n.attributes == attrSeq &&
@@ -55,7 +55,7 @@ trait NodeFactory[A <: Node] {
     }
   }
 
-  def makeText(s: String) = Text(s)
+  def makeText(s: String): Text = Text(s)
   def makeComment(s: String): Seq[Comment] =
     if (ignoreComments) Nil else List(Comment(s))
   def makeProcInstr(t: String, s: String): Seq[ProcInstr] =

shared/src/main/scala/scala/xml/factory/XMLLoader.scala

@@ -14,9 +14,10 @@ package scala
 package xml
 package factory
 
+import org.xml.sax.SAXNotRecognizedException
 import javax.xml.parsers.SAXParserFactory
-import parsing.{ FactoryAdapter, NoBindingFactoryAdapter }
-import java.io.{ InputStream, Reader, File, FileDescriptor }
+import parsing.{FactoryAdapter, NoBindingFactoryAdapter}
+import java.io.{File, FileDescriptor, InputStream, Reader}
 import java.net.URL
 
 /**
@@ -28,7 +29,7 @@ trait XMLLoader[T <: Node] {
   def adapter: FactoryAdapter = new NoBindingFactoryAdapter()
 
   private lazy val parserInstance = new ThreadLocal[SAXParser] {
-    override def initialValue = {
+    override def initialValue: SAXParser = {
       val parser = SAXParserFactory.newInstance()
       parser.setFeature("http://javax.xml.XMLConstants/feature/secure-processing", true)
       parser.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false)
@@ -52,6 +53,12 @@ trait XMLLoader[T <: Node] {
   def loadXML(source: InputSource, parser: SAXParser): T = {
     val newAdapter = adapter
 
+    try {
+      parser.setProperty("http://xml.org/sax/properties/lexical-handler", newAdapter)
+    } catch {
+      case _: SAXNotRecognizedException =>
+    }
+
     newAdapter.scopeStack = TopScope :: newAdapter.scopeStack
     parser.parse(source, newAdapter)
     newAdapter.scopeStack = newAdapter.scopeStack.tail

shared/src/main/scala/scala/xml/parsing/FactoryAdapter.scala

@@ -16,10 +16,10 @@ package parsing
 
 import scala.collection.Seq
 import org.xml.sax.Attributes
-import org.xml.sax.helpers.DefaultHandler
+import org.xml.sax.ext.DefaultHandler2
 
 // can be mixed into FactoryAdapter if desired
-trait ConsoleErrorHandler extends DefaultHandler {
+trait ConsoleErrorHandler extends DefaultHandler2 {
   // ignore warning, crimson warns even for entity resolution!
   override def warning(ex: SAXParseException): Unit = {}
   override def error(ex: SAXParseException): Unit = printError("Error", ex)
@@ -39,8 +39,8 @@ trait ConsoleErrorHandler extends DefaultHandler {
  *  namespace bindings, without relying on namespace handling of the
  *  underlying SAX parser.
  */
-abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node] {
-  var rootElem: Node = null
+abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Node] {
+  var rootElem: Node = _
 
   val buffer = new StringBuilder()
   /** List of attributes
@@ -72,7 +72,7 @@ abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node
     */
   var scopeStack = List.empty[NamespaceBinding]
 
-  var curTag: String = null
+  var curTag: String = _
   var capture: Boolean = false
 
   // abstract methods
@@ -105,6 +105,11 @@ abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node
    */
   def createProcInstr(target: String, data: String): Seq[ProcInstr]
 
+  /**
+   * creates a new comment node.
+   */
+  def createComment(characters: String): Seq[Comment]
+
   //
   // ContentHandler methods
   //
@@ -118,7 +123,7 @@ abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node
    * @param length
    */
   override def characters(ch: Array[Char], offset: Int, length: Int): Unit = {
-    if (!capture) return
+    if (!capture) ()
     // compliant: report every character
     else if (!normalizeWhitespace) buffer.appendAll(ch, offset, length)
     // normalizing whitespace is not compliant, but useful
@@ -170,7 +175,7 @@ abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node
 
         if (pre == "xmlns" || (pre == null && qname == "xmlns")) {
           val arg = if (pre == null) null else key
-          scpe = new NamespaceBinding(arg, nullIfEmpty(value), scpe)
+          scpe = NamespaceBinding(arg, nullIfEmpty(value), scpe)
         } else
           m = Attribute(Option(pre), key, Text(value), m)
       }
@@ -183,7 +188,7 @@ abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node
    * captures text, possibly normalizing whitespace
    */
   def captureText(): Unit = {
-    if (capture && buffer.length > 0)
+    if (capture && buffer.nonEmpty)
       hStack = createText(buffer.toString) :: hStack
 
     buffer.clear()
@@ -226,4 +231,10 @@ abstract class FactoryAdapter extends DefaultHandler with factory.XMLLoader[Node
     captureText()
     hStack = hStack.reverse_:::(createProcInstr(target, data).toList)
   }
+
+  override def comment(ch: Array[Char], start: Int, length: Int): Unit = {
+    captureText()
+    val commentText: String = String.valueOf(ch.slice(start, start + length))
+    hStack = hStack.reverse_:::(createComment(commentText).toList)
+  }
 }

shared/src/main/scala/scala/xml/parsing/NoBindingFactoryAdapter.scala

@@ -23,20 +23,23 @@ import factory.NodeFactory
  */
 class NoBindingFactoryAdapter extends FactoryAdapter with NodeFactory[Elem] {
   /** True.  Every XML node may contain text that the application needs */
-  def nodeContainsText(label: String) = true
+  override def nodeContainsText(label: String) = true
 
   /** From NodeFactory.  Constructs an instance of scala.xml.Elem -- TODO: deprecate as in Elem */
-  protected def create(pre: String, label: String, attrs: MetaData, scope: NamespaceBinding, children: Seq[Node]): Elem =
+  override protected def create(pre: String, label: String, attrs: MetaData, scope: NamespaceBinding, children: Seq[Node]): Elem =
     Elem(pre, label, attrs, scope, children.isEmpty, children: _*)
 
   /** From FactoryAdapter.  Creates a node. never creates the same node twice, using hash-consing.
      TODO: deprecate as in Elem, or forward to create?? */
-  def createNode(pre: String, label: String, attrs: MetaData, scope: NamespaceBinding, children: List[Node]): Elem =
+  override def createNode(pre: String, label: String, attrs: MetaData, scope: NamespaceBinding, children: List[Node]): Elem =
     Elem(pre, label, attrs, scope, children.isEmpty, children: _*)
 
   /** Creates a text node. */
-  def createText(text: String) = Text(text)
+  override def createText(text: String): Text = makeText(text)
 
   /** Creates a processing instruction. */
-  def createProcInstr(target: String, data: String) = makeProcInstr(target, data)
+  override def createProcInstr(target: String, data: String): Seq[ProcInstr] = makeProcInstr(target, data)
+
+  /** Creates a comment. */
+  override def createComment(characters: String): Seq[Comment] = makeComment(characters)
 }