Fixed SAX parsing of XML attributes.

This was utterly broken, mainly due to me overlooking it. There are now 2 new
callbacks to handle this properly:

* on_attribute: to handle a single attribute/value pair
* on_attributes: to handle a collection of attributes (as returned by
  on_attribute)

By default on_attribut returns a Hash, on_attributes in turn merges all
attribute hashes into a single one. This ensures that on_element _actually_
receives the attributes as a Hash, instead of an Array with random
nil/XML::Attribute values.

lib/oga/xml/parser.rll

@@ -154,15 +154,12 @@ element
 
 # Attributes
 
-attributes
-  = attributes_ { val[0] }
-  | _
-  ;
+attributes = attributes_ { on_attributes(val[0]) };
 
 attributes_
-  = attribute attributes
+  = attribute attributes_
     {
-      val[1].unshift(val[0])
+      val[1].unshift(val[0]) if val[0]
       val[1]
     }
   | _
@@ -171,9 +168,7 @@ attributes_
 attribute
   = attribute_name attribute_follow
     {
-      val[0].value = val[1]
-
-      val[0]
+      on_attribute(val[0][1], val[0][0], val[1])
     }
   ;
 
@@ -183,8 +178,8 @@ attribute_follow
   ;
 
 attribute_name
-  = T_ATTR           { on_attribute(val[0]) }
-  | T_ATTR_NS T_ATTR { on_attribute(val[1], val[0]) }
+  = T_ATTR { [nil, val[0]] }
+  | T_ATTR_NS T_ATTR
   ;
 
 # XML declarations
@@ -388,9 +383,21 @@ string_body_follow
   ##
   # @param [String] name
   # @param [String] ns_name
+  # @param [String] value
   # @return [Oga::XML::Attribute]
   #
-  def on_attribute(name, ns_name = nil)
-    return Attribute.new(:namespace_name => ns_name, :name => name)
+  def on_attribute(name, ns_name = nil, value = nil)
+    return Attribute.new(
+      :namespace_name => ns_name,
+      :name           => name,
+      :value          => value
+    )
+  end
+
+  ##
+  # @param [Array] attrs
+  #
+  def on_attributes(attrs)
+    return attrs
   end
 }

lib/oga/xml/sax_parser.rb

@@ -17,6 +17,8 @@ module Oga
     # * `on_text`
     # * `on_element`
     # * `on_element_children`
+    # * `on_attribute`
+    # * `on_attributes`
     # * `after_element`
     #
     # For example:
@@ -57,6 +59,14 @@ module Oga
     #       end
     #     end
     #
+    # ## Attributes
+    #
+    # Attributes returned by `on_attribute` are passed as an Hash as the 3rd
+    # argument of the `on_element` callback. The keys of this Hash are the
+    # attribute names (optionally prefixed by their namespace) and their values.
+    # You can overwrite `on_attribute` to control individual attributes and
+    # `on_attributes` to control the final set.
+    #
     class SaxParser < Parser
       ##
       # @param [Object] handler The SAX handler to delegate callbacks to.
@@ -86,7 +96,7 @@ module Oga
       # @see [Oga::XML::Parser#on_element]
       # @return [Array]
       #
-      def on_element(namespace, name, attrs = {})
+      def on_element(namespace, name, attrs = [])
         run_callback(:on_element, namespace, name, attrs)
 
         return namespace, name
@@ -101,6 +111,45 @@ module Oga
       #
       def after_element(namespace_with_name)
         run_callback(:after_element, *namespace_with_name)
+
+        return
+      end
+
+      ##
+      # Manually overwrite this method since for this one we _do_ want the
+      # return value so it can be passed to `on_element`.
+      #
+      # @see [Oga::XML::Parser#on_attribute]
+      #
+      def on_attribute(name, ns = nil, value = nil)
+        if @handler.respond_to?(:on_attribute)
+          return run_callback(:on_attribute, name, ns, value)
+        end
+
+        key = ns ? "#{ns}:#{name}" : name
+
+        return {key => value}
+      end
+
+      ##
+      # Merges the attributes together into a Hash.
+      #
+      # @param [Array] attrs
+      # @return [Hash]
+      #
+      def on_attributes(attrs)
+        if @handler.respond_to?(:on_attributes)
+          return run_callback(:on_attributes, attrs)
+        end
+
+        merged = {}
+
+        attrs.each do |pair|
+          # Hash#merge requires an extra allocation, this doesn't.
+          pair.each { |key, value| merged[key] = value }
+        end
+
+        return merged
       end
 
       private