XPath compiler support for operators in predicates

Previously the operator methods would ignore any blocks set by the
on_predicate family of methods.

lib/oga/xpath/compiler.rb

@@ -299,7 +299,7 @@ module Oga
       #
       # @see [#operator]
       #
-      def on_eq(ast, input)
+      def on_eq(ast, input, &block)
         conversion = literal('Conversion')
 
         operator(ast, input) do |left, right|
@@ -308,7 +308,10 @@ module Oga
             conversion.to_compatible_types(left, right)
           )
 
-          compatible_assign.followed_by(left.eq(right))
+          operation = left.eq(right)
+          operation = operation.if_true(&block) if block # In a predicate
+
+          compatible_assign.followed_by(operation)
         end
       end
 
@@ -317,7 +320,7 @@ module Oga
       #
       # @see [#operator]
       #
-      def on_neq(ast, input)
+      def on_neq(ast, input, &block)
         conversion = literal('Conversion')
 
         operator(ast, input) do |left, right|
@@ -326,19 +329,28 @@ module Oga
             conversion.to_compatible_types(left, right)
           )
 
-          compatible_assign.followed_by(left != right)
+          operation = left != right
+          operation = operation.if_true(&block) if block # In a predicate
+
+          compatible_assign.followed_by(operation)
         end
       end
 
       OPERATORS.each do |callback, (conv_method, ruby_method)|
-        define_method(callback) do |ast, input|
+        define_method(callback) do |ast, input, &block|
           conversion = literal('Conversion')
 
           operator(ast, input) do |left, right|
-            lval = conversion.__send__(conv_method, left)
-            rval = conversion.__send__(conv_method, right)
+            lval      = conversion.__send__(conv_method, left)
+            rval      = conversion.__send__(conv_method, right)
+            operation = lval.__send__(ruby_method, rval)
 
-            lval.__send__(ruby_method, rval)
+            # In a predicate
+            if block
+              operation = conversion.to_boolean(operation).if_true(&block)
+            end
+
+            operation
           end
         end
       end
@@ -348,10 +360,11 @@ module Oga
       #
       # @see [#operator]
       #
-      def on_pipe(ast, input)
+      def on_pipe(ast, input, &block)
         left, right = *ast
 
-        union = unique_literal('union')
+        union      = unique_literal('union')
+        conversion = literal('Conversion')
 
         left_push = process(left, input) do |node|
           union << node
@@ -361,10 +374,18 @@ module Oga
           union << node
         end
 
-        union.assign(literal(XML::NodeSet).new)
+        push_ast = union.assign(literal(XML::NodeSet).new)
           .followed_by(left_push)
           .followed_by(right_push)
-          .followed_by(union)
+
+        # In a predicate
+        if block
+          final = conversion.to_boolean(union).if_true(&block)
+        else
+          final = union
+        end
+
+        push_ast.followed_by(final)
       end
 
       # @param [AST::Node] ast