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

pylib/gyp/generator/scons.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 gyp
 import gyp.common
 import gyp.SCons as SCons
 import os.path
 import pprint
 import re
@@ skipping 446 matching lines @@
                  'target_name': target_name,
              })
     if int(action.get('process_outputs_as_sources', 0)):
       fp.write('input_files.extend(_outputs)\n')
     fp.write('prerequisites.extend(_outputs)\n')
     fp.write('target_files.extend(_outputs)\n')
 
   rules = spec.get('rules', [])
   for rule in rules:
     name = rule['rule_name'].translate(string.maketrans(' ()-', '____'))
-    a = ['cd', src_subdir, '&&'] + rule['action']
     message = rule.get('message')
     if message:
         message = repr(message)
     if int(rule.get('process_outputs_as_sources', 0)):
       poas_line = '_processed_input_files.extend(_generated)'
     else:
       poas_line = '_processed_input_files.append(infile)'
     inputs = [FixPath(f, src_subdir_) for f in rule.get('inputs', [])]
     outputs = [FixPath(f, src_subdir_) for f in rule.get('outputs', [])]
+    # Skip a rule with no action and no inputs.
+    if 'action' not in rule and not rule.get('rule_sources', []):
+      continue
+    a = ['cd', src_subdir, '&&'] + rule['action']
     fp.write(_rule_template % {
                  'inputs' : pprint.pformat(inputs),
                  'outputs' : pprint.pformat(outputs),
                  'action' : pprint.pformat(a),
                  'extension' : rule['extension'],
                  'name' : name,
                  'message' : message,
                  'process_outputs_as_sources_line' : poas_line,
                  'src_dir' : src_subdir_,
              })
@@ skipping 549 matching lines @@
       bf, target = gyp.common.ParseQualifiedTarget(t)[:2]
       target_filename = TargetFilename(target, bf, options.suffix)
       tpath = gyp.common.RelativePath(target_filename, output_dir)
       sconscript_files[target] = tpath
 
     output_filename = output_path(output_filename)
     if sconscript_files:
       GenerateSConscriptWrapper(build_file, data[build_file], basename,
                                 output_filename, sconscript_files,
                                 default_configuration)