Add new `include` config option.

This new option allows users to provide a list of external config files
which will be evaluated when beets starts.

This is useful for keeping private settings (e.g. API keys) out of the
main configuration file.

beets/util/confit.py

@@ -779,6 +779,16 @@ class Configuration(RootView):
         if os.path.isfile(filename):
             self.add(ConfigSource(load_yaml(filename) or {}, filename))
 
+        try:
+            included_filenames = self['include'].get(list)
+        except NotFoundError:
+            included_filenames = []
+
+        for filename in included_filenames:
+            filename = os.path.join(self.config_dir(), filename)
+            if os.path.isfile(filename):
+                self.add(ConfigSource(load_yaml(filename) or {}, filename))
+
     def _add_default_source(self):
         """Add the package's default configuration settings. This looks
         for a YAML file located inside the package for the module

docs/changelog.rst

@@ -22,6 +22,7 @@ The new features:
   trigger a "lots of music" warning. :bug:`1577`
 * :doc:`/plugins/plexupdate`: A new ``library_name`` option allows you to select
   which Plex library to update. :bug:`1572` :bug:`1595`
+* Add new `include` config option to allow including external config files.
 
 Fixes:
 

docs/reference/config.rst

@@ -64,6 +64,12 @@ plugins
 A space-separated list of plugin module names to load. See
 :ref:`using-plugins`.
 
+include
+~~~~~~~
+
+A space-separated list of extra configuration files to include.
+Filenames are relative to the directory containing ``config.yaml``.
+
 pluginpath
 ~~~~~~~~~~