Fix bug in ninja generator when there's no default action.

pylib/gyp/generator/ninja.py

 # Copyright (c) 2012 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import copy
 import gyp
 import gyp.common
 import gyp.msvs_emulation
 import gyp.MSVSVersion
 import gyp.system_test
@@ skipping 525 matching lines @@
       self.ninja.newline()
 
     return all_outputs
 
   def WriteRules(self, rules, extra_sources, prebuild,
                  extra_mac_bundle_resources):
     all_outputs = []
     for rule in rules:
       # First write out a rule for the rule action.
       name = rule['rule_name']
+      # Skip a rule with no action and no inputs.
+      if 'action' not in rule and not rule.get('rule_sources', []):
+        continue
       args = rule['action']
       description = self.GenerateDescription(
           'RULE',
           rule.get('message', None),
           ('%s ' + generator_default_variables['RULE_INPUT_PATH']) % name)
       is_cygwin = (self.msvs_settings.IsRuleRunUnderCygwin(rule)
                    if self.flavor == 'win' else False)
       args = [self.msvs_settings.ConvertVSMacros(arg, self.base_to_build)
               for arg in args] if self.flavor == 'win' else args
       rule_name = self.WriteNewNinjaRule(name, args, description, is_cygwin)
@@ skipping 972 matching lines @@
 
   user_config = params.get('generator_flags', {}).get('config', None)
   if user_config:
     GenerateOutputForConfig(target_list, target_dicts, data, params,
                             user_config)
   else:
     config_names = target_dicts[target_list[0]]['configurations'].keys()
     for config_name in config_names:
       GenerateOutputForConfig(target_list, target_dicts, data, params,
                               config_name)