From 9a0db27487d3d28ca3286975c0c8cf13b5f27fc6 Mon Sep 17 00:00:00 2001
From: "Aaron S. Hawley" <aaron.s.hawley@gmail.com>
Date: Tue, 28 Aug 2018 11:54:28 -0400
Subject: [PATCH] Fix failure for empty attribute match

Running the following invalid attribute search, properly throws an
IllegalArgumentException.

    scala> <x/> \ "@"
    java.lang.IllegalArgumentException: @

    scala> <x/> \@ ""
    java.lang.IllegalArgumentException: @

There's no such thing as an empty attribute.

However, when the improper matching value is used against more than
just one element, no error is thrown, just an empty NodeSeq is
returned:

    scala> <x><y/><z/></x>.child \ "@"
    res1: scala.xml.NodeSeq = NodeSeq()

It should be a failure.

Similarly, the attribute search method, is similarly affected.

    scala> <x><y/><z/></x>.child \@ ""
    res1: scala.xml.NodeSeq = NodeSeq()

This was identified while writing ScalaCheck property tests.
---
 shared/src/main/scala/scala/xml/NodeSeq.scala |  1 +
 .../test/scala/scala/xml/AttributeTest.scala  | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/shared/src/main/scala/scala/xml/NodeSeq.scala b/shared/src/main/scala/scala/xml/NodeSeq.scala
index 07e6fe87d..18c8295b2 100644
--- a/shared/src/main/scala/scala/xml/NodeSeq.scala
+++ b/shared/src/main/scala/scala/xml/NodeSeq.scala
@@ -116,6 +116,7 @@ abstract class NodeSeq extends AbstractSeq[Node] with immutable.Seq[Node] with S
     that match {
       case ""                                        => fail
       case "_"                                       => makeSeq(!_.isAtom)
+      case "@"                                       => fail
       case _ if (that(0) == '@' && this.length == 1) => atResult
       case _                                         => makeSeq(_.label == that)
     }
diff --git a/shared/src/test/scala/scala/xml/AttributeTest.scala b/shared/src/test/scala/scala/xml/AttributeTest.scala
index 0b3891496..285d24795 100644
--- a/shared/src/test/scala/scala/xml/AttributeTest.scala
+++ b/shared/src/test/scala/scala/xml/AttributeTest.scala
@@ -154,4 +154,23 @@ class AttributeTest {
     assertEquals(List(Group(Seq(Text("1"))), Group(Seq(Text("2")))), barList)
   }
 
+  @Test(expected=classOf[IllegalArgumentException])
+  def invalidAttributeFailForOne: Unit = {
+    <x/> \ "@"
+  }
+
+  @Test(expected=classOf[IllegalArgumentException])
+  def invalidAttributeFailForMany: Unit = {
+    <x><y/><z/></x>.child \ "@"
+  }
+
+  @Test(expected=classOf[IllegalArgumentException])
+  def invalidEmptyAttributeFailForOne: Unit = {
+    <x/> \@ ""
+  }
+
+  @Test(expected=classOf[IllegalArgumentException])
+  def invalidEmptyAttributeFailForMany: Unit = {
+    <x><y/><z/></x>.child \@ ""
+  }
 }