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

pylib/gyp/generator/msvs.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 ntpath
 import os
 import posixpath
 import re
 import subprocess
@@ skipping 471 matching lines @@
   rules_filename = '%s%s.rules' % (spec['target_name'],
                                    options.suffix)
   rules_file = MSVSToolFile.Writer(os.path.join(output_dir, rules_filename),
                                    spec['target_name'])
   # Add each rule.
   for r in rules:
     rule_name = r['rule_name']
     rule_ext = r['extension']
     inputs = _FixPaths(r.get('inputs', []))
     outputs = _FixPaths(r.get('outputs', []))
+    # Skip a rule with no action and no inputs.
+    if 'action' not in r and not r.get('rule_sources', []):
+      continue
     cmd = _BuildCommandLineForRule(spec, r, has_input_path=True,
                                    do_setup_env=True)
     rules_file.AddCustomBuildRule(name=rule_name,
                                   description=r.get('message', rule_name),
                                   extensions=[rule_ext],
                                   additional_dependencies=inputs,
                                   outputs=outputs,
                                   cmd=cmd)
   # Write out rules file.
   rules_file.WriteIfChanged()
@@ skipping 1433 matching lines @@
   # MSBuild rules are implemented using three files: an XML file, a .targets
   # file and a .props file.
   # See http://blogs.msdn.com/b/vcblog/archive/2010/04/21/quick-help-on-vs2010-custom-build-rule.aspx
   # for more details.
   rules = spec.get('rules', [])
   rules_native = [r for r in rules if not int(r.get('msvs_external_rule', 0))]
   rules_external = [r for r in rules if int(r.get('msvs_external_rule', 0))]
 
   msbuild_rules = []
   for rule in rules_native:
+    # Skip a rule with no action and no inputs.
+    if 'action' not in rule and not rule.get('rule_sources', []):
+      continue
     msbuild_rule = MSBuildRule(rule, spec)
     msbuild_rules.append(msbuild_rule)
     extension_to_rule_name[msbuild_rule.extension] = msbuild_rule.rule_name
   if msbuild_rules:
     base = spec['target_name'] + options.suffix
     props_name = base + '.props'
     targets_name = base + '.targets'
     xml_name = base + '.xml'
 
     props_files_of_rules.add(props_name)
@@ skipping 1155 matching lines @@
   action_spec.extend(
       # TODO(jeanluc) 'Document' for all or just if as_sources?
       [['FileType', 'Document'],
        ['Command', command],
        ['Message', description],
        ['Outputs', outputs]
       ])
   if additional_inputs:
     action_spec.append(['AdditionalInputs', additional_inputs])
   actions_spec.append(action_spec)