Fix XML rendering

xml/src/main/scala/fs2/data/xml/XmlEvent.scala

@@ -33,7 +33,13 @@ object XmlEvent {
 
   case class XmlDecl(version: String, encoding: Option[String], standalone: Option[Boolean]) extends XmlEvent
 
-  case class StartTag(name: QName, attributes: List[Attr], isEmpty: Boolean) extends XmlEvent
+  case class StartTag(name: QName, attributes: List[Attr], isEmpty: Boolean) extends XmlEvent {
+    def render(collapseEmpty: Boolean): String = {
+      val end = if (collapseEmpty && isEmpty) "/>" else ">"
+      val attrs = attributes.foldMap[String] { case Attr(n, v) => show""" $n="${v.foldMap[String](_.render)}"""" }
+      show"""<$name$attrs$end"""
+    }
+  }
 
   case class XmlCharRef(value: Int) extends XmlTexty {
     def render = f"&#x$value%04x;"
@@ -44,7 +50,7 @@ object XmlEvent {
   }
 
   case class XmlString(s: String, isCDATA: Boolean) extends XmlTexty {
-    def render = s
+    def render = if (isCDATA) show"<![CDATA[$s]]>" else s
   }
 
   case class XmlPI(target: String, content: String) extends XmlEvent
@@ -58,15 +64,12 @@ object XmlEvent {
   case class Comment(comment: String) extends XmlEvent
 
   implicit val show: Show[XmlEvent] = Show.show {
-    case XmlString(s, false) => s
-    case XmlString(s, true)  => show"<![CDATA[$s]]>"
-    case t: XmlTexty         => t.render
-    case StartTag(n, attrs, isEmpty) =>
-      show"<${n} ${attrs.map { case Attr(n, v) => show"$n='${v.map(_.render).mkString_("")}'" }.mkString_("")}>"
+    case t: XmlTexty      => t.render
+    case s: StartTag      => s.render(false)
     case EndTag(n)        => show"</$n>"
     case Comment(content) => s"<!--$content-->"
     case XmlDecl(version, encoding, standalone) =>
-      s"""<?xml version="$version"${encoding.map(e => s""" encoding="$e"""").getOrElse("")}${standalone.map {
+      s"""<?xml version="$version"${encoding.foldMap(e => s""" encoding="$e"""")}${standalone.foldMap {
           case true  => s""" standalone="yes""""
           case false => s""" standalone="no""""
         }}?>"""

xml/src/main/scala/fs2/data/xml/package.scala

@@ -75,6 +75,18 @@ package object xml {
   def normalize[F[_]]: Pipe[F, XmlEvent, XmlEvent] =
     Normalizer.pipe[F]
 
+  /**
+    * Render the incoming xml events to their string representation. The output will be concise,
+    * without additional (or original) whitespace and with empty tags being collapsed to the short self-closed form <x/>
+    * if collapseEmpty is true. Preserves chunking, each String in the output will correspond to one event in the input.
+    */
+  def render[F[_]](collapseEmpty: Boolean = true): Pipe[F, XmlEvent, String] =
+    _.zipWithPrevious.map {
+      case (_, st: XmlEvent.StartTag)                                                 => st.render(collapseEmpty)
+      case (Some(XmlEvent.StartTag(_, _, true)), XmlEvent.EndTag(_)) if collapseEmpty => ""
+      case (_, event)                                                                 => event.show
+    }
+
   val ncNameStart = CharRanges.fromRanges(
     ('A', 'Z'),
     ('_', '_'),

xml/src/test/scala/fs2/data/xml/XmlEventShowTest.scala

@@ -0,0 +1,50 @@
+package fs2.data.xml
+
+import cats.Show
+import cats.syntax.all._
+import weaver._
+
+object XmlEventShowTest extends SimpleIOSuite {
+
+  implicit def showX[X <: XmlEvent]: Show[X] = XmlEvent.show.narrow
+
+  import XmlEvent._
+
+  pureTest("texts") {
+    expect.eql("foo", XmlString("foo", false).show) &&
+    expect.eql("<![CDATA[foo]]>", XmlString("foo", true).show) &&
+    expect.eql("&#x04d2;", XmlCharRef(0x04d2).show) &&
+    expect.eql("&amp;", XmlEntityRef("amp").show)
+  }
+
+  pureTest("tags") {
+    val hello = QName("hello")
+    val preHello = QName(Some("pre"), "hello")
+    val attrA = Attr(QName("a"), List(XmlString("1", false)))
+    val attrB = Attr(QName("b"), List(XmlString("2", false)))
+
+    expect.eql("<hello>", StartTag(hello, Nil, false).show) &&
+    expect.eql("<hello>", StartTag(hello, Nil, true).show) && // ideally, this would use />
+    expect.eql("<pre:hello>", StartTag(preHello, Nil, false).show) &&
+    expect.eql("<hello a=\"1\">", StartTag(hello, List(attrA), false).show) &&
+    expect.eql("<hello a=\"1\" b=\"2\">", StartTag(hello, List(attrA, attrB), false).show) &&
+    expect.eql("</hello>", EndTag(hello).show)
+  }
+
+  pureTest("comments") {
+    expect.eql("<!--something-->", Comment("something").show)
+  }
+
+  pureTest("declarations") {
+    expect.eql("<?xml version=\"1.0\"?>", XmlDecl("1.0", None, None).show) &&
+    expect.eql("<?xml version=\"1.0\" encoding=\"utf-8\"?>", XmlDecl("1.0", Some("utf-8"), None).show) &&
+    expect.eql("<?xml version=\"1.0\" standalone=\"yes\"?>", XmlDecl("1.0", None, Some(true)).show) &&
+    expect.eql("<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>",
+               XmlDecl("1.0", Some("utf-8"), Some(true)).show)
+  }
+
+  pureTest("pi") {
+    expect.eql("<?target content?>", XmlPI("target", "content").show)
+  }
+
+}

xml/src/test/scala/fs2/data/xml/XmlRenderTest.scala

@@ -0,0 +1,25 @@
+package fs2.data.xml
+
+import cats.effect.IO
+import cats.syntax.all._
+import weaver._
+
+object XmlRenderTest extends SimpleIOSuite {
+
+  test("renders xml with self-closing tags") {
+    val result =
+      xml"""<?xml version="1.0" encoding="utf-8"?><doc><no-content/></doc>""".through(render()).compile.string
+    result.liftTo[IO].map { result =>
+      expect.eql("""<?xml version="1.0" encoding="utf-8"?><doc><no-content/></doc>""", result)
+    }
+  }
+
+  test("renders xml without self-closing tags if disabled") {
+    val result =
+      xml"""<?xml version="1.0" encoding="utf-8"?><doc><no-content/></doc>""".through(render(false)).compile.string
+    result.liftTo[IO].map { result =>
+      expect.eql("""<?xml version="1.0" encoding="utf-8"?><doc><no-content></no-content></doc>""", result)
+    }
+  }
+
+}