1 files changed, 77 insertions, 0 deletions
diff --git a/src/mailman/utilities/plugins.py b/src/mailman/utilities/plugins.py
new file mode 100644
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+++ b/src/mailman/utilities/plugins.py
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+# Copyright (C) 2009-2017 by the Free Software Foundation, Inc.
+#
+# This file is part of GNU Mailman.
+#
+# GNU Mailman is free software: you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free
+# Software Foundation, either version 3 of the License, or (at your option)
+# any later version.
+#
+# GNU Mailman 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 General Public License for
+# more details.
+#
+# You should have received a copy of the GNU General Public License along with
+# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Plugin utilities."""
+
+from lazr.config import as_boolean
+from mailman.config import config
+from mailman.utilities.modules import find_components
+from pkg_resources import resource_isdir
+from public import public
+
+
+@public
+def find_pluggable_components(subpackage, interface):
+    """Find components which conform to a given interface, in subpackage.
+
+    :param subpackage: Mailman subpackage to search. The search is also
+    done inside the corresponding plugins subpackages.
+    :type subpackage: string
+    :param interface: The interface that returned objects must conform to.
+    :type interface: `Interface`
+    :return: The sequence of matching components.
+    :rtype: objects implementing `interface`
+    """
+    yield from find_components('mailman.' + subpackage, interface)
+    package_roots = [plugin.path
+                     for name, plugin in config.plugin_configs
+                     if as_boolean(plugin.enable) and plugin.path]
+    for package_root in package_roots:
+        package = package_root + '.' + subpackage
+        if resource_isdir(package_root, subpackage):
+            yield from find_components(package, interface)
+
+
+@public
+def add_pluggable_components(subpackage, interface, mapping):
+    """Add components to a given mapping.
+
+    Similarly to `find_pluggable_components()` this inspects all modules in a
+    given mailman and plugin's subpackage looking for objects that conform to
+    a given interface.  All such found objects (unless decorated with
+    `@abstract_component`) are added to the given mapping, keyed by the
+    object's `.name` attribute, which is required.  It is a fatal error if
+    that key already exists in the mapping.
+
+    :param subpackage: The subpackage path to search.
+    :type subpackage: string
+    :param interface: The interface that returned objects must conform to.
+        Objects found must have a `.name` attribute containing a unique
+        string.
+    :type interface: `Interface`
+    :param mapping: The mapping to add the found components to.
+    :type mapping: A dict-like mapping.  This only needs to support
+        containment tests (e.g. `in` and `not in`) and `__setitem__()`.
+    :raises RuntimeError: when a duplicate key is found.
+    """
+    for component_class in find_pluggable_components(subpackage, interface):
+        component = component_class()
+        if component.name in mapping:
+            raise RuntimeError(     # pragma: nocover
+                'Duplicate key "{}" found in {}; previously {}'.format(
+                    component.name, component, mapping[component.name]))
+        mapping[component.name] = component