Handle XML namespace declarations even when the underlying parser is …

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

@@ -629,6 +629,35 @@ class XMLTestJVM {
     // does not work: roundtripNodes("<a/> <!-- epilogue -->")
   }
 
+  // using non-namespace-aware parser, this always worked;
+  // using namespace-aware parser, this works with FactoryAdapter enhanced to handle startPrefixMapping() events;
+  // see https://github.com/scala/scala-xml/issues/506
+  def roundtrip(namespaceAware: Boolean, xml: String): Unit = {
+    val parserFactory: javax.xml.parsers.SAXParserFactory = javax.xml.parsers.SAXParserFactory.newInstance()
+    parserFactory.setFeature("http://javax.xml.XMLConstants/feature/secure-processing", true)
+    parserFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false)
+    parserFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true)
+    parserFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", false)
+    parserFactory.setFeature("http://xml.org/sax/features/external-general-entities", false)
+    parserFactory.setFeature("http://xml.org/sax/features/resolve-dtd-uris", false)
+    parserFactory.setNamespaceAware(namespaceAware)
+    parserFactory.setXIncludeAware(namespaceAware)
+
+    assertEquals(xml, XML.withSAXParser(parserFactory.newSAXParser()).loadString(xml).toString())
+  }
+
+  @UnitTest
+  def namespaceUnaware: Unit =
+    roundtrip(namespaceAware = false, """<book xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"/>""")
+
+  @UnitTest
+  def namespaceAware: Unit =
+    roundtrip(namespaceAware = true, """<book xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"/>""")
+
+  @UnitTest
+  def namespaceAware2: Unit =
+    roundtrip(namespaceAware = true, """<book xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"><svg xmlns:svg="http://www.w3.org/2000/svg"/></book>""")
+
   @UnitTest
   def nodeSeqNs: Unit = {
     val x = {

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

@@ -211,10 +211,25 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
           m = Attribute(Option(pre), key, Text(value), m)
       }
 
+      // Add namespace bindings for the prefix mappings declared by this element
+      // (if there are any, the parser is namespace-aware, and no namespace bindings were delivered as attributes).
+      // All `startPrefixMapping()` events will occur immediately before the corresponding `startElement()` event.
+      for ((prefix: String, uri: String) <- prefixMappings)
+        scpe = NamespaceBinding(if (prefix.isEmpty) null else prefix, uri, scpe)
+
+      // Once the `prefixMappings` are processed into `scpe`, the list is emptied out
+      // so that already-declared namespaces are not re-declared on the nested elements.
+      prefixMappings = List.empty
+
       scopeStack = scpe :: scopeStack
       attribStack =  m :: attribStack
     }
 
+  private var prefixMappings: List[(String, String)] = List.empty
+
+  override def startPrefixMapping(prefix: String, uri: String): Unit =
+    prefixMappings = (prefix, uri) :: prefixMappings
+
   /**
    * Captures text or cdata.
    */