Merge minrk/conf.d-->ankostis/cfg_loader_fact to render ipython#242 e…

…xtensible

- Deprecate Application class-attribute:
  - python_config_loader_class
  - json_config_loader_class
  replaced by `supported_cfg_loaders` ordered mapping:
    {.ext: loader-class}
- To extend with a new config-file, simply add its loader class in the
`supported_cfg_loaders` mapping.
- Merge-conflicts resolved in Application.

traitlets/config/application.py

@@ -132,9 +132,16 @@ class Application(SingletonConfigurable):
     keyvalue_description = Unicode(keyvalue_description)
     subcommand_description = Unicode(subcommand_description)
 
+    #: .. deprecated:: 5.0.0
+    #:     Replaced by `supported_cfg_loaders` ordered-map.
     python_config_loader_class = PyFileConfigLoader
     json_config_loader_class = JSONFileConfigLoader
 
+    supported_cfg_loaders = OrderedDict([
+        ('.py', PyFileConfigLoader),
+        ('.json', JSONFileConfigLoader)])
+
+
     # The usage and example string that goes at the end of the help string.
     examples = Unicode()
 
@@ -705,12 +712,12 @@ def parse_command_line(self, argv=None):
         self.extra_args = loader.extra_args
 
     @classmethod
-    def _make_loaders(cls, basefilename, path=None, **kw):
+    def _make_loader_for_ext(cls, config_fname, path, **kw):
         """
         Builds the list of config-loaders to try.
 
-        :param str basefilename:
-            The config filename without extension (`.py` or `.json`).
+        :param str config_fname:
+            The config filename with extension (e.g. '.py', '.json').
         :param path:
             The dirpath to search for the config file on, or a sequence of
             paths to try in order.
@@ -720,12 +727,10 @@ def _make_loaders(cls, basefilename, path=None, **kw):
         :return:
             a list, currently `python-load, json-loader].
         """
-        pyloader = cls.python_config_loader_class(basefilename+'.py',
-                                                  path=path, **kw)
-        jsonloader = cls.json_config_loader_class(basefilename+'.json',
-                                                  path=path, **kw)
-
-        return [pyloader, jsonloader]
+        for ext, loader in cls.supported_cfg_loaders.items():
+            if config_fname.endswith(ext):
+                return loader(config_fname, path, **kw)
+        raise AssertionError("Unknown config-file extension: %s" % config_fname)
 
     @classmethod
     def _load_config_files(cls, basefilename, path=None, log=None, raise_config_file_errors=False):
@@ -740,11 +745,21 @@ def _load_config_files(cls, basefilename, path=None, log=None, raise_config_file
             # path list is in descending priority order, so load files backwards:
             if log:
                 log.debug("Looking for %s in %s", basefilename, path or os.getcwd())
-            loaders = cls._make_loaders(basefilename, path=path, log=log)
+            loaders = [cls._make_loader_for_ext(basefilename + ext,
+                                                path=path, log=log)
+                       for ext in cls.supported_cfg_loaders]
+            # load conf.d/config files in lorder
+            conf_d = os.path.join(path, basefilename + '.d')
+            if os.path.isdir(conf_d):
+                supported_cfg_extensions = tuple(cls.supported_cfg_loaders)
+                for filename in sorted(os.listdir(conf_d)):
+                    if filename.endswith(supported_cfg_extensions):
+                        loaders.append(cls._make_loader_for_ext(filename,
+                                                                path=conf_d, log=log))
+            config = None
             loaded = []
             filenames = []
             for loader in loaders:
-                config = None
                 try:
                     config = loader.load_config()
                 except ConfigFileNotFound: