Use puppetlabs_spec_helper to test parser functions

Without this patch applied rspec-puppet reaches deep inside of Puppet
and uses an unsupported and private interface to obtain functions and
scope instances.  This is a problem because Puppet Labs considers
internal classes such as Puppet::Parser::Scope as private and internal.

We change these classes without warning and this is a maintenance issue
for third party testing tools.

This patch fixes this maintenance problem by using the compatibility
layer implemented in the puppetlabs_spec_helper.  When we change the
internal behavior of private classes such as Puppet::Parser::Scope,
we'll update the spec helper module methods to provide a version
agnostic way to get instances of these internal objects.

As an example, a supported way to get a scope instance is:

    PuppetlabsSpec::PuppetInternals.scope

Instead of the private and unsupported method of:

    Puppet::Parser::Scope.new

This patch introduces a Gem dependency onto the puppetlabs_spec_helper
gem.

Gemfile

@@ -6,3 +6,4 @@ rspecversion = ENV.key?('RSPEC_VERSION') ? "= #{ENV['RSPEC_VERSION']}" : ['>= 2.
 gem 'rake'
 gem 'rspec', rspecversion
 gem 'puppet', puppetversion
+gem 'puppetlabs_spec_helper'

lib/rspec-puppet/example/function_example_group.rb

@@ -1,13 +1,15 @@
+require 'puppetlabs_spec_helper/puppetlabs_spec/puppet_internals'
+
 module RSpec::Puppet
   module FunctionExampleGroup
     include RSpec::Puppet::FunctionMatchers
+    PuppetInternals = PuppetlabsSpec::PuppetInternals
 
     def subject
       function_name = self.class.top_level_description.downcase
 
       Puppet[:modulepath] = self.respond_to?(:module_path) ? module_path : RSpec.configuration.module_path
       Puppet[:libdir] = Dir["#{Puppet[:modulepath]}/*/lib"].entries.join(File::PATH_SEPARATOR)
-      Puppet::Parser::Functions.autoloader.loadall
 
       # if we specify a pre_condition, we should ensure that we compile that code
       # into a catalog that is accessible from the scope where the function is called
@@ -23,20 +25,28 @@ module RSpec::Puppet
         # we need to get a compiler, b/c we can attach that to a scope
         @compiler = build_compiler(nodename, facts_val)
       else
-        @compiler = nil
+        @compiler = PuppetInternals.compiler
       end
 
-      scope = Puppet::Parser::Scope.new(:compiler => @compiler)
+      scope = PuppetInternals.scope(:compiler => @compiler)
 
-      scope.method "function_#{function_name}".to_sym
+      # Return the method instance for the function.  This can be used with
+      # method.call
+      method = PuppetInternals.function_method(function_name, :scope => scope)
     end
 
     def compiler
       @compiler
     end
+
     # get a compiler with an attached compiled catalog
     def build_compiler(node_name, fact_values)
-      compiler = Puppet::Parser::Compiler.new(Puppet::Node.new(node_name, :parameters => fact_values))
+      node_options = {
+        :name    => node_name,
+        :options => { :parameters => fact_values },
+      }
+      node = PuppetInternals.node(node_options)
+      compiler = PuppetInternals.compiler(:node => node)
       compiler.compile
       compiler
     end