[ruby/rexml] Fix attribute's default namespace behavior

NOTE: It's a backward incompatible change. If we have any serious
problems with this change, we may revert this change.

The XML namespace specification says the default namespace doesn't
apply to attribute names but it does in REXML without this change:

https://www.w3.org/TR/xml-names/#uniqAttrs

> the default namespace does not apply to attribute names

REXML reports a parse error for the following XML that is described as
a valid XML in the XML nsmaspace specification without this change:

    <!-- http://www.w3.org is bound to n1 and is the default -->
    <x xmlns:n1="http://www.w3.org"
       xmlns="http://www.w3.org" >
      <good a="1"     b="2" />
      <good a="1"     n1:a="2" />
    </x>

If attribute doesn't have prefix, the attribute should return "" for
both #prefix and #namespace.

https://github.com/ruby/rexml/commit/9e4fd552bc

1 files changed, 10 insertions, 11 deletions

diff --git a/lib/rexml/attribute.rb b/lib/rexml/attribute.rb
index 37671cf15f..8933a013a2 100644
--- a/lib/rexml/attribute.rb
+++ b/lib/rexml/attribute.rb
@@ -67,15 +67,11 @@ module REXML
     #  e.add_attribute( "nsa:a", "aval" )
     #  e.add_attribute( "b", "bval" )
     #  e.attributes.get_attribute( "a" ).prefix   # -> "nsa"
-    #  e.attributes.get_attribute( "b" ).prefix   # -> "elns"
+    #  e.attributes.get_attribute( "b" ).prefix   # -> ""
     #  a = Attribute.new( "x", "y" )
     #  a.prefix                                   # -> ""
     def prefix
-      pf = super
-      if pf == ""
-        pf = @element.prefix if @element
-      end
-      pf
+      super
     end
 
     # Returns the namespace URL, if defined, or nil otherwise
@@ -87,9 +83,8 @@ module REXML
     #  e.attribute("ns:a").namespace # => "http://url"
     #  e.attribute("nsx:a").namespace # => nil
     #
-    # TODO: This method should always return nil for no namespace
-    # attribute. Because the default namespace doesn't apply to
-    # attribute name.
+    # This method always returns "" for no namespace attribute. Because
+    # the default namespace doesn't apply to attribute names.
     #
     # From https://www.w3.org/TR/xml-names/#uniqAttrs
     #
@@ -99,10 +94,14 @@ module REXML
     #  e.add_namespace("", "http://example.com/")
     #  e.namespace # => "http://example.com/"
     #  e.add_attribute("a", "b")
-    #  e.attribute("a").namespace # => nil
+    #  e.attribute("a").namespace # => ""
     def namespace arg=nil
       arg = prefix if arg.nil?
-      @element.namespace arg
+      if arg == ""
+        ""
+      else
+        @element.namespace(arg)
+      end
     end
 
     # Returns true if other is an Attribute and has the same name and value,