Add virtualenv option for openstack_pip

As described in comments, is allows you to specify a virtualenv path
in the package_options with the openstack_pip provider.  This allows
you to install packages into a virtualenv directly.

Change-Id: Ib6d41bdadf7db93b2c28e04ace8d219583b8a68f

README.md

@@ -3,3 +3,21 @@
 ## Overview
 
 Configures PIP.
+
+## Usage
+
+To use the module, create a package with the `openstack_pip` provider.
+
+You can optionally pass a `virtualenv` path in `package_settings` to
+install the package within a given virtualenv
+
+```
+include ::pip
+
+package { 'tox':
+  ensure => 'latest',
+  provider => openstack_pip,
+  require => Class[pip],
+  package_settings  => {'virtualenv' => '/path/to/virtualenv/bin'},
+}
+```

lib/puppet/provider/package/openstack_pip.rb

@@ -1,3 +1,4 @@
+# coding: utf-8
 require 'puppet/provider/package'
 require 'net/http'
 require 'xmlrpc/client'
@@ -7,9 +8,36 @@ Puppet::Type.type(:package).provide(:openstack_pip, :parent => :pip) do
 
   desc "Python packages via `pip` with mirrors."
 
-  has_feature :installable, :uninstallable, :upgradeable, :versionable
+  has_feature :installable, :uninstallable, :upgradeable, :versionable, :package_settings
 
-  commands :pip => 'pip'
+  # Why do we do this?
+  #
+  #  To summarize, implementing self.instances in your provider means
+  #  that you need to return an array of provider instances that have
+  #  been discovered on the current system and all the current property
+  #  values (we call these values the ‘is’ values for the properties,
+  #  since each value IS the current value of the property on the
+  #  system). It’s recommended to only implement self.instances if you
+  #  can gather all resource property values in a reasonably ‘cheap’
+  #  manner (i.e. a single system call, read from a single file, or some
+  #  similar low-IO means). Implementing self.instances not only gives
+  #  you the ability to run puppet resource (which also affords you a
+  #  quick-and-dirty way of testing your provider without creating unit
+  #  tests by simply running puppet resource in debug mode and checking
+  #  the output), but it also allows the ‘resources’ resource to work its
+  #  magic (If you’ve never heard of the ‘resources’ resource, check this
+  #  link for more information on this terribly/awesomely named resource
+  #  type).
+  #
+  # http://garylarizza.com/blog/2013/12/15/seriously-what-is-this-provider-doing/
+  #
+  # Because we have the package_settings "virtualenv" it doesn't
+  # really make a lot of sense to gather "all" resources.  Since this
+  # is just a caching method, override it from the base version (which
+  # does a global "pip --list") to do nothing.
+  def self.instances
+    [ ]
+  end
 
   def self.outdated
     @outdated ||= pip(['list', '--outdated'])
@@ -30,4 +58,26 @@ Puppet::Type.type(:package).provide(:openstack_pip, :parent => :pip) do
     end
     return latest
   end
+
+  # This overrides the pip calls to prefix a virtualenv set within
+  # package_settings, which is otherwise unsued for pip.
+  # Unfortunately without patching puppet we can't define our own
+  # resource names, which is why we overload package_settings.
+  #
+  def lazy_pip(*args)
+    pip(*args)
+  rescue NoMethodError => e
+    if @resource[:package_settings]['virtualenv']
+      pip_path = String(@resource[:package_settings]['virtualenv'] + "/pip")
+      Puppet.debug("Using #{pip_path}")
+      self.class.commands :pip => pip_path
+    else
+      # copied from parent class; see notes there
+      if pathname = self.class.cmd.map { |c| which(c) }.find{ |c| c != nil }
+        self.class.commands :pip => File.basename(pathname)
+      end
+    end
+    pip(*args)
+  end
+
 end