Honor the configured email collection module(s), even w/ entry points

entry points make for an obvious default collection, but if config
declares a particular list of modules, that should win

rattail/mail.py

@@ -89,13 +89,43 @@ class EmailHandler(object):
         self.config = config
         self.enum = self.config.get_enum()
 
+    def use_entry_points(self):
+        """
+        Returns a boolean indicating if the app should get its list of
+        available emails from the setuptools entry points, instead of
+        the (legacy) ``[rattail.mail] emails`` config setting.
+        """
+        return self.config.getbool('rattail.mail', 'emails.use_entry_points',
+                                   default=False)
+
     def get_all_emails(self, **kwargs):
         """
         Retrieve the complete set of all Email profiles exposed by the
         app and installed packages.
         """
+        # TODO: maybe deprecate this at some point?
+        if not self.use_entry_points():
+            # nb. this is the legacy behavior
+            return dict([(email.key or email.__name__, email)
+                         for email in self.iter_emails(warn=False)])
+
+        # this is the future..
         emails = {}
-        modules = load_entry_points('rattail.emails').values()
+
+        # first get *all* email modules, per entry points
+        all_modules = load_entry_points('rattail.emails').values()
+
+        # but maybe the app config says only to use certain modules
+        app_modules = self.config.getlist('rattail.mail', 'emails')
+
+        # figure out which modules we should actually use
+        if app_modules:
+            modules = [import_module_path(m)
+                       for m in app_modules]
+        else:
+            modules = all_modules
+
+        # and collect all email profiles from those modules
         for module in modules:
             mod_emails = self.get_emails_from_module(module)
             emails.update(dict([(email.key or email.__name__, email)
@@ -114,15 +144,6 @@ class EmailHandler(object):
                 emails.append(obj)
         return emails
 
-    def use_entry_points(self):
-        """
-        Returns a boolean indicating if the app should get its list of
-        available emails from the setuptools entry points, instead of
-        the (legacy) ``[rattail.mail] emails`` config setting.
-        """
-        return self.config.getbool('rattail.mail', 'emails.use_entry_points',
-                                   default=False)
-
     def get_available_emails(self, **kwargs):
         """
         Retrieve the set of "available" Email profiles, i.e. those