From 00f52639673dc4db32ac9302e2a70483492d621e Mon Sep 17 00:00:00 2001
From: J08nY
Date: Tue, 4 Jul 2017 21:18:23 +0200
Subject: Instantiate components only in add_components, not at lower levels.

 - The scan_module and find_components functions are also useful
   when they don't instantiate the components they load, and
   instantiation is left to add_components.
---
 src/mailman/utilities/modules.py            | 27 ++++++++++++++-------------
 src/mailman/utilities/tests/test_modules.py |  4 ++--
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/src/mailman/utilities/modules.py b/src/mailman/utilities/modules.py
index 155a34ed2..eb8f7184a 100644
--- a/src/mailman/utilities/modules.py
+++ b/src/mailman/utilities/modules.py
@@ -71,19 +71,18 @@ def call_name(dotted_name, *args, **kws):
 
 
 def scan_module(module, interface):
-    """Return all the object in a module that conform to an interface.
+    """Return all the items in a module that conform to an interface.
 
     Scan every item named in the module's `__all__`.  If that item conforms to
     the given interface, *and* the item is not declared as an
-    `@abstract_component`, then instantiate the item and return the resulting
-    instance.
+    `@abstract_component`, then return the item.
 
     :param module: A module object.
     :type module: module
     :param interface: The interface that returned objects must conform to.
     :type interface: `Interface`
-    :return: The sequence of instantiated matching components.
-    :rtype: instantiated objects implementing `interface`
+    :return: The sequence of matching components.
+    :rtype: items implementing `interface`
     """
     missing = object()
     for name in module.__all__:
@@ -99,7 +98,7 @@ def scan_module(module, interface):
                 # where the marker has been placed.  The value of
                 # __abstract_component__ doesn't matter, only its presence.
                 and '__abstract_component__' not in component.__dict__):
-            yield component()
+            yield component
 
 
 @public
@@ -107,15 +106,15 @@ def find_components(package, interface):
     """Find components which conform to a given interface.
 
     Search all the modules in a given package, returning an iterator over all
-    objects found that conform to the given interface, unless that object is
+    items found that conform to the given interface, unless that object is
     decorated with `@abstract_component`.
 
     :param package: The package path to search.
     :type package: string
     :param interface: The interface that returned objects must conform to.
     :type interface: `Interface`
-    :return: The sequence of instantiated matching components.
-    :rtype: instantiated objects implementing `interface`
+    :return: The sequence of matching components.
+    :rtype: items implementing `interface`
     """
     for filename in resource_listdir(package, ''):
         basename, extension = os.path.splitext(filename)
@@ -135,9 +134,10 @@ def add_components(package, interface, 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.
+    found objects (unless decorated with `@abstract_component`) are
+    instantiated and 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
@@ -150,7 +150,8 @@ 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_class in find_components(package, interface):
+        component = component_class()
         if component.name in mapping:
             raise RuntimeError(
                 'Duplicate key "{}" found in {}; previously {}'.format(
diff --git a/src/mailman/utilities/tests/test_modules.py b/src/mailman/utilities/tests/test_modules.py
index 82d44cff4..08ec3848a 100644
--- a/src/mailman/utilities/tests/test_modules.py
+++ b/src/mailman/utilities/tests/test_modules.py
@@ -99,8 +99,8 @@ class BadStyle:
                      in find_components('mypackage', IStyle)]
             self.assertEqual(names, ['good-style'])
 
-    def test_find_components_no_instantiate(self):
-        # find_components() now instantiates the class unless it's been
+    def test_find_components_abstract_component(self):
+        # find_components() finds the class unless it's been
         # decorated with the @abstract_component decorator.
         with ExitStack() as resources:
             # Creating a temporary directory and adding it to sys.path.
-- 
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