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#!/usr/bin/env python3
#
# Copyright (C) 2016 Codethink Limited
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
# Authors:
# Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
import os
from .exceptions import PluginError
# A Context for loading plugin types
#
# Args:
# plugin_base (PluginBase): The main PluginBase object to work with
# base_type (type): A base object type for this context
# searchpath (list): A list of paths to search for plugins
#
# Since multiple pipelines can be processed recursively
# within the same interpretor, it's important that we have
# one context associated to the processing of a given pipeline,
# this way sources and element types which are particular to
# a given BuildStream project are isolated to their respective
# Pipelines.
#
class PluginContext():
def __init__(self, plugin_base, base_type, searchpath=None):
if not searchpath:
raise PluginError("Cannot create plugin context without any searchpath")
self.base_type = base_type # The base class plugins derive from
self.source = None # The PluginSource object
self.types = {} # Plugin type lookup table by kind
self.load_plugins(plugin_base, searchpath)
# lookup():
#
# Fetches a type loaded from a plugin in this plugin context
#
# Args:
# kind (str): The kind of Plugin to create
#
# Returns: the type associated with the given kind
#
# Raises: PluginError
#
def lookup(self, kind):
if kind not in self.types:
raise PluginError("No %s type registered for kind '%s'" %
(self.base_type.__name__, kind))
return self.types[kind]
def load_plugins(self, base, searchpath):
# Raise an error if we have more than one plugin with the same name
self.assert_searchpath(searchpath)
self.source = base.make_plugin_source(searchpath=searchpath)
for kind in self.source.list_plugins():
self.load_plugin(kind)
def load_plugin(self, kind):
plugin = self.source.load_plugin(kind)
try:
plugin_type = plugin.setup()
except AttributeError as e:
raise PluginError("%s plugin '%s' did not provide a setup() function" %
(self.base_type.__name__, kind)) from e
except TypeError as e:
raise PluginError("setup symbol in %s plugin '%s' is not a function" %
(self.base_type.__name__, kind)) from e
self.assert_plugin(kind, plugin_type)
self.types[kind] = plugin_type
def assert_plugin(self, kind, plugin_type):
if kind in self.types:
raise PluginError("Tried to register %s plugin for existing kind '%s' "
"(already registered %s)" %
(self.base_type.__name__, kind, self.types[kind].__name__))
try:
if not issubclass(plugin_type, self.base_type):
raise PluginError("%s plugin '%s' returned type '%s', which is not a subclass of %s" %
(self.base_type.__name__, kind,
plugin_type.__name__,
self.base_type.__name__))
except TypeError as e:
raise PluginError("%s plugin '%s' returned something that is not a type (expected subclass of %s)" %
(self.base_type.__name__, kind,
self.base_type.__name__)) from e
# We want a PluginError when trying to create a context
# where more than one plugin has the same name
def assert_searchpath(self, searchpath):
names = []
fullnames = []
for path in searchpath:
for filename in os.listdir(path):
basename = os.path.basename(filename)
name, extension = os.path.splitext(basename)
if extension == '.py' and name != '__init__':
fullname = os.path.join(path, filename)
if name in names:
idx = names.index(name)
raise PluginError("Failed to register %s plugin '%s' from: %s\n"
"%s plugin '%s' is already registered by: %s" %
(self.base_type.__name__, name, fullname,
self.base_type.__name__, name, fullnames[idx]))
names.append(name)
fullnames.append(fullname)
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