Make XmlDeclaration a ProcessingInstruction

This allows Oga to parse documents that contain an XML declaration at a
place other than at the document root. Oga still only assigns the XML
declaration to the document whenever it is at the top-level. This
matches libxml/XML specification behaviour as far as I can tell.

lib/oga.rb

@@ -35,8 +35,8 @@ require 'oga/xml/character_node'
 require 'oga/xml/text'
 require 'oga/xml/comment'
 require 'oga/xml/cdata'
-require 'oga/xml/xml_declaration'
 require 'oga/xml/processing_instruction'
+require 'oga/xml/xml_declaration'
 require 'oga/xml/doctype'
 require 'oga/xml/namespace'
 require 'oga/xml/default_namespace'

lib/oga/xml/generator.rb

@@ -48,12 +48,14 @@ module Oga
             callback = :on_comment
           when Oga::XML::Attribute
             callback = :on_attribute
+          when Oga::XML::XmlDeclaration
+            # This must come before ProcessingInstruction since XmlDeclaration
+            # extends ProcessingInstruction.
+            callback = :on_xml_declaration
           when Oga::XML::ProcessingInstruction
             callback = :on_processing_instruction
           when Oga::XML::Doctype
             callback = :on_doctype
-          when Oga::XML::XmlDeclaration
-            callback = :on_xml_declaration
           when Oga::XML::Document
             callback = :on_document
             children = true

lib/oga/xml/xml_declaration.rb

@@ -1,9 +1,7 @@
 module Oga
   module XML
     # Class containing information about an XML declaration tag.
-    class XmlDeclaration
-      include ToXML
-
+    class XmlDeclaration < ProcessingInstruction
       # @return [String]
       attr_accessor :version
 
@@ -20,9 +18,12 @@ module Oga
       # @option options [String] :encoding
       # @option options [String] :standalone
       def initialize(options = {})
+        super
+
         @version    = options[:version] || '1.0'
         @encoding   = options[:encoding] || 'UTF-8'
         @standalone = options[:standalone]
+        @name       = 'xml'
       end
 
       # @return [String]

spec/oga/xml/parser/xml_declaration_spec.rb

@@ -36,4 +36,28 @@ describe Oga::XML::Parser do
       @node.encoding.should == 'foo'
     end
   end
+
+  it 'parses an XML declaration inside an element' do
+    document = parse('<foo><?xml ?></foo>')
+
+    document.children[0].should be_an_instance_of(Oga::XML::Element)
+    document.children[0].children[0].should be_an_instance_of(Oga::XML::XmlDeclaration)
+  end
+
+  it 'parses an XML declaration preceded by an element' do
+    document = parse('<foo /><?xml ?>')
+
+    document.xml_declaration.should be_an_instance_of(Oga::XML::XmlDeclaration)
+    document.children[0].should be_an_instance_of(Oga::XML::Element)
+  end
+
+  it 'parses an XML declaration preceded by an element with a common ancestor' do
+    document = parse('<root><a /><?xml ?></root>')
+    root = document.children[0]
+
+    root.children[0].should be_an_instance_of(Oga::XML::Element)
+    root.children[1].should be_an_instance_of(Oga::XML::XmlDeclaration)
+
+    root.children[1].previous.should == root.children[0]
+  end
 end

spec/oga/xml/xml_declaration_spec.rb

@@ -28,6 +28,12 @@ describe Oga::XML::XmlDeclaration do
     end
   end
 
+  describe '#name' do
+    it 'returns the name of the node' do
+      described_class.new.name.should == 'xml'
+    end
+  end
+
   describe '#to_xml' do
     before do
       @instance = described_class.new(

spec/oga/xpath/compiler/type_tests/processing_instruction_spec.rb

@@ -1,24 +1,36 @@
 require 'spec_helper'
 
 describe Oga::XPath::Compiler do
-  before do
-    @document = parse('<a><?a foo ?><b><?b bar ?></b></a>')
+  describe 'using a regular processing instruction' do
+    before do
+      @document = parse('<a><?a foo ?><b><?b bar ?></b></a>')
 
-    @proc_ins1 = @document.children[0].children[0]
-    @proc_ins2 = @document.children[0].children[1].children[0]
-  end
-
-  describe 'relative to a document' do
-    describe 'a/processing-instruction()' do
-      it 'returns a NodeSet' do
-        evaluate_xpath(@document).should == node_set(@proc_ins1)
-      end
+      @proc_ins1 = @document.children[0].children[0]
+      @proc_ins2 = @document.children[0].children[1].children[0]
     end
 
-    describe 'a/b/processing-instruction()' do
-      it 'returns a NodeSet' do
-        evaluate_xpath(@document).should == node_set(@proc_ins2)
+    describe 'relative to a document' do
+      describe 'a/processing-instruction()' do
+        it 'returns a NodeSet' do
+          evaluate_xpath(@document).should == node_set(@proc_ins1)
+        end
       end
+
+      describe 'a/b/processing-instruction()' do
+        it 'returns a NodeSet' do
+          evaluate_xpath(@document).should == node_set(@proc_ins2)
+        end
+      end
+    end
+  end
+
+  describe 'using an XML declaration' do
+    it 'returns a NodeSet containing the XmlDeclaration' do
+      document = parse('<root><?xml version="1.0" ?></root>')
+      xml_decl = document.children[0].children[0]
+
+      evaluate_xpath(document, 'root/processing-instruction()')
+        .should == node_set(xml_decl)
     end
   end
 end