Better handling of incorrect XML/HTML tags

The XML/HTML lexer is now capable of processing most invalid XML/HTML
(that I can think of at least). This is achieved by inserting missing
closing tags (where needed) and/or ignoring excessive closing tags. For
example, HTML such as this:

    <a></a></p>

Results in the following tokens:

    [:T_ELEM_START, nil, 1]
    [:T_ELEM_NAME, 'a', 1]
    [:T_ELEM_CLOSE, nil, 1]

In turn this HTML:

    <a>

Results in these tokens:

    [:T_ELEM_START, nil, 1]
    [:T_ELEM_NAME, 'a', 1]
    [:T_ELEM_CLOSE, nil, 1]

Fixes #84

lib/oga/xml/lexer.rb

@@ -151,6 +151,11 @@ module Oga
         read_data do |chunk|
           advance_native(chunk)
         end
+
+        # Add any missing closing tags
+        unless @elements.empty?
+          @elements.length.times { on_element_end }
+        end
       ensure
         @block = nil
       end
@@ -377,7 +382,7 @@ module Oga
       # @param [String] name The name of the element, including namespace.
       #
       def on_element_name(name)
-        @elements << name if html?
+        @elements << name
 
         add_token(:T_ELEM_NAME, name)
       end
@@ -410,9 +415,11 @@ module Oga
       # Called on the closing tag of an element.
       #
       def on_element_end
+        return if @elements.empty?
+
         add_token(:T_ELEM_END)
 
-        @elements.pop if html?
+        @elements.pop
       end
 
       ##

spec/oga/xml/lexer/elements_spec.rb

@@ -5,21 +5,24 @@ describe Oga::XML::Lexer do
     it 'lexes an opening element' do
       lex('<p>').should == [
         [:T_ELEM_START, nil, 1],
-        [:T_ELEM_NAME, 'p', 1]
+        [:T_ELEM_NAME, 'p', 1],
+        [:T_ELEM_END, nil, 1]
       ]
     end
 
     it 'lexes an opening element with a stray double quote' do
       lex('<p">').should == [
         [:T_ELEM_START, nil, 1],
-        [:T_ELEM_NAME, 'p', 1]
+        [:T_ELEM_NAME, 'p', 1],
+        [:T_ELEM_END, nil, 1]
       ]
     end
 
     it 'lexes an opening element with a stray double quoted string' do
       lex('<p"">').should == [
         [:T_ELEM_START, nil, 1],
-        [:T_ELEM_NAME, 'p', 1]
+        [:T_ELEM_NAME, 'p', 1],
+        [:T_ELEM_END, nil, 1]
       ]
     end
 
@@ -60,7 +63,8 @@ describe Oga::XML::Lexer do
       lex('Foo<p>').should == [
         [:T_TEXT, 'Foo', 1],
         [:T_ELEM_START, nil, 1],
-        [:T_ELEM_NAME, 'p', 1]
+        [:T_ELEM_NAME, 'p', 1],
+        [:T_ELEM_END, nil, 1]
       ]
     end
 

spec/oga/xml/lexer/invalid_elements_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe Oga::XML::Lexer do
+  describe 'invalid elements' do
+    it 'adds missing closing tags' do
+      lex('<a>').should == [
+        [:T_ELEM_START, nil, 1],
+        [:T_ELEM_NAME, 'a', 1],
+        [:T_ELEM_END, nil, 1]
+      ]
+    end
+
+    it 'ignores closing tags without opening tags' do
+      lex('</a>').should == []
+    end
+
+    it 'ignores excessive closing tags' do
+      lex('<a></a></b>').should == [
+        [:T_ELEM_START, nil, 1],
+        [:T_ELEM_NAME, 'a', 1],
+        [:T_ELEM_END, nil, 1]
+      ]
+    end
+  end
+end

spec/oga/xml/parser/error_spec.rb

@@ -3,13 +3,7 @@ require 'spec_helper'
 describe Oga::XML::Parser do
   describe 'raising syntax errors' do
     before do
-      @invalid_xml = <<-EOF.strip
-<person>
-  <name>Alice</name>
-  <age>25
-  <nationality>Dutch</nationality>
-</person>
-      EOF
+      @invalid_xml = '<x:y:z></z>'
     end
 
     it 'raises a LL::ParserError' do
@@ -17,16 +11,15 @@ describe Oga::XML::Parser do
     end
 
     it 'includes the line number when using a String as input' do
-      parse_error(@invalid_xml).should =~ /on line 5/
+      parse_error(@invalid_xml).should =~ /on line 1/
     end
 
     it 'includes the line number when using an IO as input' do
-      parse_error(StringIO.new(@invalid_xml)).should =~ /on line 5/
+      parse_error(StringIO.new(@invalid_xml)).should =~ /on line 1/
     end
 
     it 'uses more friendly error messages when available' do
-      parse_error('<foo>').should ==
-        'Unexpected end of input, expected element closing tag instead on line 1'
+      parse_error('<x:y:z>').should =~ /Unexpected element namespace/
     end
   end
 end