Optimization of Element#namespace and Element#namespaces with Document#enable_namespaces_cache

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

Co-authored-by: tomoya ishida <tomoyapenguin@gmail.com>
Co-authored-by: Sutou Kouhei <kou@clear-code.com>

Author: 3 people

lib/rexml/document.rb

@@ -443,6 +443,17 @@ def record_entity_expansion
       end
     end
 
+    attr_accessor :namespaces_cache
+
+    def enable_namespaces_cache
+      self.namespaces_cache = {}
+      begin
+        yield
+      ensure
+        self.namespaces_cache = nil
+      end
+    end
+
     def document
       self
     end

lib/rexml/element.rb

@@ -589,10 +589,12 @@ def prefixes
     #   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
+      namespaces_cache = root.document&.namespaces_cache
+      if namespaces_cache
+        namespaces_cache[self] ||= calculate_namespaces
+      else
+        calculate_namespaces
+      end
     end
 
     # :call-seq:
@@ -619,17 +621,9 @@ def namespace(prefix=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[prefix]
+
       ns = '' if ns.nil? and prefix == 'xmlns'
       return ns
     end
@@ -1516,8 +1510,11 @@ def write(output=$stdout, indent=-1, transitive=false, ie_hack=false)
       formatter.write( self, output )
     end
 
-
     private
+    def calculate_namespaces
+      (parent ? parent.namespaces : {}).merge(attributes.namespaces)
+    end
+
     def __to_xpath_helper node
       rv = node.expanded_name.clone
       if node.parent

lib/rexml/xpath_parser.rb

@@ -78,7 +78,15 @@ def variables=( vars={} )
 
     def parse path, nodeset
       path_stack = @parser.parse( path )
-      match( path_stack, nodeset )
+      if nodeset.first.node_type == :attribute
+        match( path_stack, nodeset )
+      else
+        nodeset.first.document.enable_namespaces_cache do
+          # New document level cache is created and available in this block.
+          # This API is thread unsafe. Users can't change this document in this block.
+          match( path_stack, nodeset )
+        end
+      end
     end
 
     def get_first path, nodeset
@@ -492,24 +500,18 @@ 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
+                  raw_node.name == name and raw_node.namespace == get_namespace(raw_node, prefix)
                 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
+                raw_node.name == name and raw_node.namespace == get_namespace(raw_node, prefix)
               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
+                raw_node.name == name and raw_node.namespace == get_namespace(raw_node.element, prefix)
               end
             else
               false