Handle unprefixed attributes in Element#attribute correctly

lib/rexml/element.rb

@@ -1270,27 +1270,14 @@ def [](name_or_index)
     # With arguments +name+ and +namespace+ given,
     # returns the value of the named attribute if it exists, otherwise +nil+:
     #
-    #   xml_string = "<root xmlns:a='a' a:x='a:x' x='x'/>"
+    #   xml_string = "<root xmlns:a='http://example.com/a' a:x='a:x' x='x'/>"
     #   document = REXML::Document.new(xml_string)
     #   document.root.attribute("x")      # => x='x'
-    #   document.root.attribute("x", "a") # => a:x='a:x'
+    #   document.root.attribute("x", "http://example.com/a") # => a:x='a:x'
     #
     def attribute( name, namespace=nil )
       prefix = namespaces.key(namespace) if namespace
-      prefix = nil if prefix == 'xmlns'
-
-      ret_val =
-        attributes.get_attribute( prefix ? "#{prefix}:#{name}" : name )
-
-      return ret_val unless ret_val.nil?
-      return nil if prefix.nil?
-
-      # now check that prefix'es namespace is not the same as the
-      # default namespace
-      return nil unless ( namespaces[ prefix ] == namespaces[ 'xmlns' ] )
-
-      attributes.get_attribute( name )
-
+      attributes.get_attribute( prefix ? "#{prefix}:#{name}" : name )
     end
 
     # :call-seq:

test/test_core.rb

@@ -1451,12 +1451,6 @@ def test_ticket_95
       assert_equal(out1,out2)
     end
 
-    def test_ticket_102
-      doc = REXML::Document.new '<doc xmlns="ns"><item name="foo"/></doc>'
-      assert_equal( "foo", doc.root.elements["*:item"].attribute("name","ns").to_s )
-      assert_equal( "item", doc.root.elements["*:item[@name='foo']"].name )
-    end
-
     def test_ticket_14
       # Per .2.5 Node Tests of XPath spec
       assert_raise( REXML::UndefinedNamespaceException,
@@ -1478,18 +1472,6 @@ def test_ticket_105
       assert_equal( 1, d.root.children.size )
     end
 
-    # phantom namespace same as default namespace
-    def test_ticket_121
-      doc = REXML::Document.new(
-        '<doc xmlns="ns" xmlns:phantom="ns"><item name="foo">text</item></doc>'
-      )
-      assert_equal 'text', doc.text( "/*:doc/*:item[@name='foo']" )
-      assert_equal "name='foo'",
-        doc.root.elements["*:item"].attribute("name", "ns").inspect
-      assert_equal "<item name='foo'>text</item>",
-        doc.root.elements["*:item[@name='foo']"].to_s
-    end
-
     def test_ticket_135
       bean_element = REXML::Element.new("bean")
       textToAdd = "(&#38;(|(memberof=CN=somegroupabcdefgh,OU=OUsucks,DC=hookemhorns,DC=com)(mail=*someco.com))(acct=%u)(!(extraparameter:2.2.222.222222.2.2.222:=2)))"
@@ -1521,6 +1503,20 @@ def test_ticket_138
                    REXML::Document.new(doc.root.to_s).root.attributes.to_h)
     end
 
+    def test_unprefixed_attribute
+      doc = REXML::Document.new(<<~XML)
+        <root xmlns="http://example.org/test">
+          <foo bar="baz" />
+        </root>
+      XML
+
+      assert_equal("baz", doc.elements["//foo"].attribute("bar")&.value)
+
+      # Unprefixed attributes have no prefix and the default namespace is not applied.
+      # See https://www.w3.org/TR/xml-names/#defaulting.
+      assert_equal(nil, doc.elements["//foo"].attribute("bar", "http://example.org/test")&.value)
+    end
+
     def test_empty_doc
       assert(REXML::Document.new('').children.empty?)
     end