Better conversion of types to numbers.

The XPath number() function should also be capable of converting booleans to
numbers, something it previously was not able to do. In order to do this
reliably we can't rely on the string() function as this would make it impossible
to distinguish between literal string values and booleans. This is due to
true(), which returns a TrueClass, being converted to the string "true". This
string in turn can't be converted to a float.

lib/oga/xpath/evaluator.rb

@@ -780,7 +780,7 @@ module Oga
           convert = process(expression, context)
 
           if convert.is_a?(XML::NodeSet)
-            convert = convert.first
+            convert = convert[0]
           end
         else
           convert = current_node
@@ -815,9 +815,28 @@ module Oga
       # @return [Float]
       #
       def on_call_number(context, expression = nil)
-        str_val = on_call_string(context, expression)
+        convert = nil
 
-        return Float(str_val) rescue Float::NAN
+        if expression
+          exp_retval = process(expression, context)
+
+          if exp_retval.is_a?(XML::NodeSet)
+            convert = first_node_text(exp_retval)
+
+          elsif exp_retval == true
+            convert = 1.0
+
+          elsif exp_retval == false
+            convert = 0.0
+
+          elsif exp_retval
+            convert = exp_retval
+          end
+        else
+          convert = current_node.text
+        end
+
+        return Float(convert) rescue Float::NAN
       end
 
       ##

spec/oga/xpath/evaluator/calls/number_spec.rb

@@ -15,6 +15,14 @@ describe Oga::XPath::Evaluator do
       @evaluator.evaluate('number("10.5")').should == 10.5
     end
 
+    example 'convert boolean true to a number' do
+      @evaluator.evaluate('number(true())').should == 1.0
+    end
+
+    example 'convert boolean false to a number' do
+      @evaluator.evaluate('number(false())').should be_zero
+    end
+
     example 'convert a node set to a number' do
       @evaluator.evaluate('number(root/a)').should == 10.0
     end
@@ -30,5 +38,9 @@ describe Oga::XPath::Evaluator do
     example 'return NaN for values that can not be converted to floats' do
       @evaluator.evaluate('number("a")').should be_nan
     end
+
+    example 'return NaN for empty node sets' do
+      @evaluator.evaluate('number(foo)').should be_nan
+    end
   end
 end