Add function ensure_resource and defined_with_params

This commit adds 2 new functions with unit tests.

defined_with_params works similarily to puppet's defined
function, except it allows you to also specify a hash of
params. defined_with_params will return true if a resource
also exists that matches the specified type/title (just like
with defined) as well as all of the specified params.

ensure_resource is a function that basically combines defined_with_params
with create_resources to conditionally create resources only if the
specified resource (title, type, params) does not already exist.

These functions are created to serve as an alternative to using
defined as follows:

    if ! defined(Package['some_package']) {
      package { 'some_package': ensure => present,
    }

The issue with this usage is that there is no guarentee about
what parameters were set in the previous definition of the package
that made its way into the catalog.

ensure_resource could be used instead, as:

    ensure_resource('package', 'some_package', { 'ensure' => 'present' })

This will creat the package resources only if another resource does
not exist with the specified parameters.

lib/puppet/parser/functions/defined_with_params.rb

@@ -0,0 +1,33 @@
+# Test whether a given class or definition is defined
+require 'puppet/parser/functions'
+
+Puppet::Parser::Functions.newfunction(:defined_with_params,
+                                      :type => :rvalue,
+                                      :doc => <<-'ENDOFDOC'
+Takes a resource reference and an optional hash of attributes.
+
+Returns true if a resource with the specified attributes has already been added
+to the catalog, and false otherwise.
+
+    user { 'dan':
+      ensure => present,
+    }
+
+    if ! defined_with_params(User[dan], {'ensure' => 'present' }) {
+      user { 'dan': ensure => present, }
+    }
+ENDOFDOC
+) do |vals|
+  reference, params = vals
+  raise(ArgumentError, 'Must specify a reference') unless reference
+  params ||= {}
+  ret = false
+  if resource = findresource(reference.to_s)
+    matches = params.collect do |key, value|
+      resource[key] == value
+    end
+    ret = params.empty? || !matches.include?(false)
+  end
+  Puppet.debug("Resource #{reference} was not determined to be defined")
+  ret
+end

lib/puppet/parser/functions/ensure_resource.rb

@@ -0,0 +1,28 @@
+# Test whether a given class or definition is defined
+require 'puppet/parser/functions'
+
+Puppet::Parser::Functions.newfunction(:ensure_resource,
+                                      :type => :statement,
+                                      :doc => <<-'ENDOFDOC'
+Takes a resource type, title, and a list of attributes that describe a
+resource.
+
+    user { 'dan':
+      ensure => present,
+    }
+
+This example only creates the resource if it does not already exist:
+
+    ensure_resource('user, 'dan', {'ensure' => 'present' })
+ENDOFDOC
+) do |vals|
+  type, title, params = vals
+  raise(ArgumentError, 'Must specify a type') unless type
+  raise(ArgumentError, 'Must specify a title') unless title
+  params ||= {}
+  if function_defined_with_params(["#{type}[#{title}]", params])
+    Puppet.debug("Resource #{type}[#{title}] does not need to be created b/c it already exists")
+  else
+    function_create_resources([type.capitalize, { title => params }])
+  end
+end

spec/functions/defined_with_params_spec.rb

@@ -0,0 +1,31 @@
+#! /usr/bin/env ruby -S rspec
+require 'spec_helper'
+
+require 'rspec-puppet'
+describe 'defined_with_params' do
+  describe 'when a resource is not specified' do
+    it { should run.with_params().and_raise_error(ArgumentError) }
+  end
+  describe 'when compared against a resource with no attributes' do
+    let :pre_condition do
+      'user { "dan": }'
+    end
+    it do
+      should run.with_params('User[dan]', {}).and_return(true)
+      should run.with_params('User[bob]', {}).and_return(false)
+      should run.with_params('User[dan]', {'foo' => 'bar'}).and_return(false)
+    end
+  end
+
+  describe 'when comparted against a resource with attributes' do
+    let :pre_condition do
+      'user { "dan": ensure => present, shell => "/bin/csh", managehome => false}'
+    end
+    it do
+      should run.with_params('User[dan]', {}).and_return(true)
+      should run.with_params('User[dan]', {'ensure' => 'present'}).and_return(true)
+      should run.with_params('User[dan]', {'ensure' => 'present', 'managehome' => false}).and_return(true)
+      should run.with_params('User[dan]', {'ensure' => 'absent', 'managehome' => false}).and_return(false)
+    end
+  end
+end

spec/functions/ensure_resource_spec.rb

@@ -0,0 +1,35 @@
+#! /usr/bin/env ruby -S rspec
+require 'spec_helper'
+
+require 'rspec-puppet'
+describe 'ensure_resource' do
+  describe 'when a type or title is not specified' do
+    it do
+      should run.with_params().and_raise_error(ArgumentError)
+      should run.with_params(['type']).and_raise_error(ArgumentError)
+    end
+  end
+  describe 'when compared against a resource with no attributes' do
+    let :pre_condition do
+      'user { "dan": }'
+    end
+    it do
+      should run.with_params('user', 'dan', {})
+      compiler.catalog.resource('User[dan]').to_s.should == 'User[dan]'
+    end
+  end
+
+  describe 'when comparted against a resource with attributes' do
+    let :pre_condition do
+      'user { "dan": ensure => present, shell => "/bin/csh", managehome => false}'
+    end
+    it do
+      # these first three should not fail
+      should run.with_params('User', 'dan', {})
+      should run.with_params('User', 'dan', {'ensure' => 'present'})
+      should run.with_params('User', 'dan', {'ensure' => 'present', 'managehome' => false})
+      #  test that this fails
+      should run.with_params('User', 'dan', {'ensure' => 'absent', 'managehome' => false}).and_raise_error(Puppet::Error)
+    end
+  end
+end