1 files changed, 77 insertions, 40 deletions

diff --git a/src/mailman/utilities/modules.py b/src/mailman/utilities/modules.py
index 155a34ed2..48cee1a0e 100644
--- a/src/mailman/utilities/modules.py
+++ b/src/mailman/utilities/modules.py
@@ -22,7 +22,7 @@ import sys
 
 from contextlib import contextmanager
 from importlib import import_module
-from pkg_resources import resource_filename, resource_listdir
+from pkg_resources import resource_filename, resource_isdir, resource_listdir
 from public import public
 
 
@@ -70,6 +70,32 @@ def call_name(dotted_name, *args, **kws):
     return named_callable(*args, **kws)
 
 
+@public
+def expand_path(url):
+    """Expand a python: path, returning the absolute file system path."""
+    # Is the context coming from a file system or Python path?
+    if url.startswith('python:'):
+        resource_path = url[7:]
+        package, dot, resource = resource_path.rpartition('.')
+        return resource_filename(package, resource + '.cfg')
+    else:
+        return url
+
+
+@public
+@contextmanager
+def hacked_sys_modules(name, module):
+    old_module = sys.modules.get(name)
+    sys.modules[name] = module
+    try:
+        yield
+    finally:
+        if old_module is None:
+            del sys.modules[name]
+        else:
+            sys.modules[name] = old_module
+
+
 def scan_module(module, interface):
     """Return all the object in a module that conform to an interface.
 
@@ -102,7 +128,6 @@ def scan_module(module, interface):
             yield component()
 
 
-@public
 def find_components(package, interface):
     """Find components which conform to a given interface.
 
@@ -122,25 +147,63 @@ def find_components(package, interface):
         if extension != '.py' or basename.startswith('.'):
             continue
         module_name = '{}.{}'.format(package, basename)
-        __import__(module_name, fromlist='*')
-        module = sys.modules[module_name]
+        module = import_module(module_name)
         if not hasattr(module, '__all__'):
             continue
         yield from scan_module(module, interface)
 
 
+def find_pluggable_components(subpackage, interface):
+    """Find components which conform to a given interface.
+
+    This finds components which can be implemented in a plugin.  It will
+    search for the interface in the named subpackage, where the Python import
+    path of the subpackage will be prepended by `mailman` for system
+    components, and the various plugin names for any external components.
+
+    :param subpackage: The subpackage to search.  This is prepended by
+        'mailman' to search for system components, and each enabled plugin for
+        external components.
+    :type subpackage: str
+    :param interface: The interface that returned objects must conform to.
+    :type interface: `Interface`
+    :return: The sequence of matching components.
+    :rtype: Objects implementing `interface`
+    """
+    # This can't be imported at module level because of circular imports.
+    from mailman.config import config
+    # Return the system components first.
+    yield from find_components('mailman.' + subpackage, interface)
+    # Return all the matching components in all the subpackages of all enabled
+    # plugins.  Only enabled and existing plugins will appear in this
+    # dictionary.
+    for name, plugin_config in config.plugin_configs:
+        # If the plugin's configuration defines a components package, use
+        # that, falling back to the plugin's name.
+        package = plugin_config['component_package'].strip()
+        if len(package) == 0:
+            package = name
+        # It's possible that the plugin doesn't include the directory for this
+        # subpackage.  That's fine.
+        if resource_isdir(package, subpackage):
+            plugin_package = '{}.{}'.format(package, subpackage)
+            yield from find_components(plugin_package, interface)
+
+
 @public
-def add_components(package, interface, mapping):
+def add_components(subpackage, interface, mapping):
     """Add components to a given mapping.
 
-    Similarly to `find_components()` this inspects all modules in a given
-    package 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.
+    Similarly to `find_pluggable_components()` this inspects all modules
+    in the given subpackage, relative to the 'mailman' parent package,
+    and all the plugin names, that match the 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 package: The package path to search.
-    :type package: string
+    :param subpackage: The subpackage path to search.
+    :type subpackage: str
     :param interface: The interface that returned objects must conform to.
         Objects found must have a `.name` attribute containing a unique
         string.
@@ -150,35 +213,9 @@ def add_components(package, interface, mapping):
         containment tests (e.g. `in` and `not in`) and `__setitem__()`.
     :raises RuntimeError: when a duplicate key is found.
     """
-    for component in find_components(package, interface):
+    for component in find_pluggable_components(subpackage, interface):
         if component.name in mapping:
-            raise RuntimeError(
+            raise RuntimeError(     # pragma: nocover
                 'Duplicate key "{}" found in {}; previously {}'.format(
                     component.name, component, mapping[component.name]))
         mapping[component.name] = component
-
-
-@public
-def expand_path(url):
-    """Expand a python: path, returning the absolute file system path."""
-    # Is the context coming from a file system or Python path?
-    if url.startswith('python:'):
-        resource_path = url[7:]
-        package, dot, resource = resource_path.rpartition('.')
-        return resource_filename(package, resource + '.cfg')
-    else:
-        return url
-
-
-@public
-@contextmanager
-def hacked_sys_modules(name, module):
-    old_module = sys.modules.get(name)
-    sys.modules[name] = module
-    try:
-        yield
-    finally:
-        if old_module is None:
-            del sys.modules[name]
-        else:
-            sys.modules[name] = old_module