Emit node() calls for certain short axes.

An axes such as "." is the same as "self::node()". To simplify things on
parser/evaluator level we'll emit the corresponding tokens for a "node()"
function call for these axes.

lib/oga/xpath/lexer.rl

@@ -23,6 +23,13 @@ module Oga
         '.'  => 'self'
       }
 
+      ##
+      # Axes that require a separate `node()` call to be emitted.
+      #
+      # @return [Array]
+      #
+      AXIS_EMIT_NODE = %w{descendant-or-self parent self}
+
       ##
       # @param [String] data The data to lex.
       #
@@ -226,6 +233,17 @@ module Oga
           value = AXIS_MAPPING[slice_input(ts, te)]
 
           add_token(:T_AXIS, value)
+
+          # Short axes that use node() as their default, implicit test. This is
+          # added on lexer level to make it easier to handle these cases on
+          # parser/evaluator level.
+          if AXIS_EMIT_NODE.include?(value)
+            add_token(:T_IDENT, 'node')
+            add_token(:T_LPAREN)
+            add_token(:T_RPAREN)
+
+            add_token(:T_SLASH) unless te == eof
+          end
         }
 
         # Operators

spec/oga/xpath/lexer/axes_spec.rb

@@ -120,6 +120,10 @@ describe Oga::XPath::Lexer do
       lex_xpath('//A').should == [
         [:T_SLASH, nil],
         [:T_AXIS, 'descendant-or-self'],
+        [:T_IDENT, 'node'],
+        [:T_LPAREN, nil],
+        [:T_RPAREN, nil],
+        [:T_SLASH, nil],
         [:T_IDENT, 'A']
       ]
     end
@@ -127,14 +131,20 @@ describe Oga::XPath::Lexer do
     example 'lex the .. axis' do
       lex_xpath('/..').should == [
         [:T_SLASH, nil],
-        [:T_AXIS, 'parent']
+        [:T_AXIS, 'parent'],
+        [:T_IDENT, 'node'],
+        [:T_LPAREN, nil],
+        [:T_RPAREN, nil],
       ]
     end
 
     example 'lex the . axis' do
       lex_xpath('/.').should == [
         [:T_SLASH, nil],
-        [:T_AXIS, 'self']
+        [:T_AXIS, 'self'],
+        [:T_IDENT, 'node'],
+        [:T_LPAREN, nil],
+        [:T_RPAREN, nil],
       ]
     end
   end

spec/oga/xpath/lexer/general_spec.rb

@@ -37,6 +37,10 @@ describe Oga::XPath::Lexer do
         [:T_IDENT, 'wikimedia'],
         [:T_SLASH, nil],
         [:T_AXIS, 'descendant-or-self'],
+        [:T_IDENT, 'node'],
+        [:T_LPAREN, nil],
+        [:T_RPAREN, nil],
+        [:T_SLASH, nil],
         [:T_IDENT, 'editions']
       ]
     end

spec/oga/xpath/parser/axes_spec.rb

@@ -120,16 +120,23 @@ describe Oga::XPath::Parser do
     example 'parse the // axis' do
       parse_xpath('//A').should == s(
         :absolute_path,
-        s(:axis, 'descendant-or-self', s(:test, nil, 'A'))
+        s(:axis, 'descendant-or-self', s(:call, 'node')),
+        s(:test, nil, 'A')
       )
     end
 
     example 'parse the .. axis' do
-      parse_xpath('/..').should == s(:absolute_path, s(:axis, 'parent'))
+      parse_xpath('/..').should == s(
+        :absolute_path,
+        s(:axis, 'parent', s(:call, 'node'))
+      )
     end
 
     example 'parse the . axis' do
-      parse_xpath('/.').should == s(:absolute_path, s(:axis, 'self'))
+      parse_xpath('/.').should == s(
+        :absolute_path,
+        s(:axis, 'self', s(:call, 'node'))
+      )
     end
   end
 end