Optimization of Element#namespace and Element#namespaces with cache

## Why?
for fix get_namespace performance
> # FIXME: This DOUBLES the time XPath searches take

Co-authored-by: tomoya ishida <tomoyapenguin@gmail.com>

Author: naitoh

lib/rexml/element.rb

@@ -588,11 +588,12 @@ def prefixes
     #   d.elements['//b'].namespaces # => {"x"=>"1", "y"=>"2"}
     #   d.elements['//c'].namespaces # => {"x"=>"1", "y"=>"2", "z"=>"3"}
     #
-    def namespaces
-      namespaces = {}
-      namespaces = parent.namespaces if parent
-      namespaces = namespaces.merge( attributes.namespaces )
-      return namespaces
+    def namespaces(cache = nil)
+      if cache
+        cache[self] ||= calculate_namespaces(cache)
+      else
+        calculate_namespaces(cache)
+      end
     end
 
     # :call-seq:
@@ -615,21 +616,13 @@ def namespaces
     #   b.namespace('y') # => "2"
     #   b.namespace('nosuch') # => nil
     #
-    def namespace(prefix=nil)
+    def namespace(prefix=nil, cache=nil)
       if prefix.nil?
         prefix = prefix()
       end
-      if prefix == ''
-        prefix = "xmlns"
-      else
-        prefix = "xmlns:#{prefix}" unless prefix[0,5] == 'xmlns'
-      end
-      ns = nil
-      target = self
-      while ns.nil? and target
-        ns = target.attributes[prefix]
-        target = target.parent
-      end
+      prefix = (prefix == '') ? 'xmlns' : prefix.delete_prefix("xmlns:")
+      ns = namespaces(cache)[prefix]
+
       ns = '' if ns.nil? and prefix == 'xmlns'
       return ns
     end
@@ -1516,8 +1509,11 @@ def write(output=$stdout, indent=-1, transitive=false, ie_hack=false)
       formatter.write( self, output )
     end
 
-
     private
+    def calculate_namespaces(cache)
+      (parent ? parent.namespaces(cache) : {}).merge(attributes.namespaces)
+    end
+
     def __to_xpath_helper node
       rv = node.expanded_name.clone
       if node.parent

lib/rexml/xpath_parser.rb

@@ -160,11 +160,11 @@ def strict?
     #
     #  1. Use the supplied namespace mapping first.
     #  2. If no mapping was supplied, use the context node to look up the namespace
-    def get_namespace( node, prefix )
+    def get_namespace( node, prefix, namespaces_cache=nil )
       if @namespaces
         return @namespaces[prefix] || ''
       else
-        return node.namespace( prefix ) if node.node_type == :element
+        return node.namespace( prefix, namespaces_cache ) if node.node_type == :element
         return ''
       end
     end
@@ -476,6 +476,7 @@ def step(path_stack, any_type: :element, order: :forward)
 
     def node_test(path_stack, nodesets, any_type: :element)
       enter(:node_test, path_stack, nodesets) if @debug
+      namespaces_cache = {}
       operator = path_stack.shift
       case operator
       when :qname
@@ -492,24 +493,30 @@ def node_test(path_stack, nodesets, any_type: :element)
                 if strict?
                   raw_node.name == name and raw_node.namespace == ""
                 else
-                  # FIXME: This DOUBLES the time XPath searches take
-                  ns = get_namespace(raw_node, prefix)
-                  raw_node.name == name and raw_node.namespace == ns
+                  if raw_node.name == name
+                    raw_node.namespace(nil, namespaces_cache) == get_namespace(raw_node, prefix, namespaces_cache)
+                  else
+                    false
+                  end
                 end
               else
-                # FIXME: This DOUBLES the time XPath searches take
-                ns = get_namespace(raw_node, prefix)
-                raw_node.name == name and raw_node.namespace == ns
+                if raw_node.name == name
+                  raw_node.namespace(nil, namespaces_cache) == get_namespace(raw_node, prefix, namespaces_cache)
+                else
+                  false
+                end
               end
             when :attribute
               if prefix.nil?
                 raw_node.name == name
               elsif prefix.empty?
                 raw_node.name == name and raw_node.namespace == ""
               else
-                # FIXME: This DOUBLES the time XPath searches take
-                ns = get_namespace(raw_node.element, prefix)
-                raw_node.name == name and raw_node.namespace == ns
+                if raw_node.name == name
+                  raw_node.namespace == get_namespace(raw_node.element, prefix)
+                else
+                  false
+                end
               end
             else
               false