Issue 2968 - Implement multi inheritance for metadata files

chainedconfigparser.py

 # coding: utf-8
 
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import os
 import io
 import ConfigParser
 from StringIO import StringIO
@@ skipping 48 matching lines @@
   def _make_parser(self, filename):
     parser = ConfigParser.SafeConfigParser()
     parser.optionxform = lambda option: option
 
     with io.open(filename, encoding='utf-8') as file:
       parser.readfp(file, filename)
 
     return parser
 
   def _get_parser_chain(self, parser, filename):
-    parsers = []
+    parsers = [(parser, filename)]
 
-    while True:
-      parsers.insert(0, (parser, filename))
+    try:
+      inherit = parser.get('default', 'inherit')
+    except (ConfigParser.NoSectionError, ConfigParser.NoOptionError):
+      return parsers
 
-      try:
-        inherit = parser.get('default', 'inherit')
-      except (ConfigParser.NoSectionError, ConfigParser.NoOptionError):
-        return parsers
+    dirname = os.path.dirname(filename)
+    for parent in inherit.split():
+      parent_filename = os.path.join(dirname, *parent.split('/'))
+      parent_parser = self._make_parser(parent_filename)
+      parsers[:0] = self._get_parser_chain(parent_parser, parent_filename)
 
-      filename = os.path.join(os.path.dirname(filename), *inherit.split('/'))
-      parser = self._make_parser(filename)
+    return parsers
 
   def _apply_diff(self, section, option, value):
     is_addition = option.endswith('+')
     is_diff = is_addition or option.endswith('-')
 
     if is_diff:
       option = option[:-1].rstrip()
       try:
         orig_value = self.get(section, option)
       except ConfigParser.NoOptionError:
@@ skipping 70 matching lines @@
     raise NotImplementedError
 
   def add_section(self, section):
     raise NotImplementedError
 
   def remove_option(self, section, option):
     raise NotImplementedError
 
   def remove_section(self, section):
     raise NotImplementedError