Add ability to extend builders via builder drivers

There are times where you may want to extend or modify the way that
giftwrap builds packages. Short of submitting a pull request or
(worse) forking the repository, there was no easy way to do so.

This change introduces builder drivers with stevedore. By merely adding
entry points in the 'giftwrap.builder.drivers', additional
implementations are now possible.

CHANGELOG.md

@@ -0,0 +1,3 @@
+2.1.0
+-----
+- feature: add builder drivers using stevedore

giftwrap/builders/__init__.py

@@ -19,9 +19,12 @@ import os
 import threading
 
 from giftwrap.gerrit import GerritReview
+from stevedore.driver import DriverManager
+from stevedore.extension import ExtensionManager
 
 from abc import abstractmethod, ABCMeta
 
+BUILDER_DRIVER_NAMESPACE = 'giftwrap.builder.drivers'
 LOG = logging.getLogger(__name__)
 
 
@@ -34,6 +37,12 @@ class Builder(object):
         self._spec = spec
         self._thread_exit = []
 
+    @staticmethod
+    def builder_names(ext_mgr=None):
+        if not ext_mgr:
+            ext_mgr = ExtensionManager(BUILDER_DRIVER_NAMESPACE)
+        return ext_mgr.names()
+
     def _get_venv_pip_path(self, venv_path):
         return os.path.join(venv_path, 'bin/pip')
 
@@ -182,5 +191,8 @@ class BuilderFactory:
 
     @staticmethod
     def create_builder(builder_type, build_spec):
-        targetclass = "%sBuilder" % builder_type.capitalize()
-        return globals()[targetclass](build_spec)
+        driver_mgr = DriverManager(namespace=BUILDER_DRIVER_NAMESPACE,
+                                   name=builder_type,
+                                   invoke_args=(build_spec,),
+                                   invoke_on_load=True)
+        return driver_mgr.driver

giftwrap/shell.py

@@ -19,7 +19,7 @@ import logging
 import signal
 import sys
 
-from giftwrap.builders import BuilderFactory
+from giftwrap.builders import Builder, BuilderFactory
 from giftwrap.build_spec import BuildSpec
 from giftwrap.color import ColorStreamHandler
 
@@ -80,7 +80,7 @@ def main():
                                          description='build giftwrap packages')
     build_subcmd.add_argument('-m', '--manifest', required=True)
     build_subcmd.add_argument('-v', '--version')
-    build_subcmd.add_argument('-t', '--type', choices=('docker', 'package'),
+    build_subcmd.add_argument('-t', '--type', choices=Builder.builder_names(),
                               required=True)
     build_subcmd.add_argument('-s', '--synchronous', dest='parallel',
                               action='store_false')

giftwrap/tests/test_builder.py

@@ -0,0 +1,34 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2015, Craig Tracey
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import unittest2 as unittest
+
+from giftwrap.builders import Builder, BUILDER_DRIVER_NAMESPACE
+from stevedore import extension
+
+
+class TestBuilder(unittest.TestCase):
+
+    def test_default_drivers(self):
+        drivers = Builder.builder_names()
+        self.assertEqual(drivers, ['docker', 'package'])
+
+    def test_additional_drivers(self):
+        em = extension.ExtensionManager(BUILDER_DRIVER_NAMESPACE)
+        em.extensions.append(extension.Extension('test', None, None, None))
+        drivers = Builder.builder_names(em)
+        self.assertEqual(drivers, ['docker', 'package', 'test'])

requirements.txt

@@ -9,3 +9,4 @@ requests
 pygerrit
 docker-py
 virtualenv
+stevedore

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = giftwrap
-version = 2.0.0
+version = 2.1.0
 summary = giftwrap - A tool to build full-stack native system packages.
 description-file =
     README.md
@@ -23,6 +23,10 @@ setup-hooks =
 console_scripts =
     giftwrap = giftwrap.shell:main
 
+giftwrap.builder.drivers =
+    package = giftwrap.builders.package_builder:PackageBuilder
+    docker = giftwrap.builders.docker_builder:DockerBuilder
+
 [files]
 packages =
     giftwrap