ninja: Don't write subninjas for ninja files that end up being empty.

pylib/gyp/generator/ninja.py

 # Copyright (c) 2013 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 hashlib
 import multiprocessing
 import os.path
 import re
 import signal
 import subprocess
 import sys
 import gyp
 import gyp.common
 import gyp.msvs_emulation
 import gyp.MSVSUtil as MSVSUtil
 import gyp.xcode_emulation
+from cStringIO import StringIO
 
 from gyp.common import GetEnvironFallback
 import gyp.ninja_syntax as ninja_syntax
 
 generator_default_variables = {
   'EXECUTABLE_PREFIX': '',
   'EXECUTABLE_SUFFIX': '',
   'STATIC_LIB_PREFIX': 'lib',
   'STATIC_LIB_SUFFIX': '.a',
   'SHARED_LIB_PREFIX': 'lib',
@@ skipping 1984 matching lines @@
       gyp.xcode_emulation.MergeGlobalXcodeSettingsToSpec(data[build_file], spec)
 
     build_file = gyp.common.RelativePath(build_file, options.toplevel_dir)
 
     base_path = os.path.dirname(build_file)
     obj = 'obj'
     if toolset != 'target':
       obj += '.' + toolset
     output_file = os.path.join(obj, base_path, name + '.ninja')
 
+    ninja_output = StringIO()
     writer = NinjaWriter(qualified_target, target_outputs, base_path, build_dir,
-                         OpenOutput(os.path.join(toplevel_build, output_file)),
+                         ninja_output,
                          toplevel_build, output_file,
                          flavor, toplevel_dir=options.toplevel_dir)
-    master_ninja.subninja(output_file)
+    target = writer.WriteSpec(spec, config_name, generator_flags)
 
-    target = writer.WriteSpec(spec, config_name, generator_flags)
+    if ninja_output.tell() > 0:
+      # Only create files for ninja files that actually have contents.
+      with OpenOutput(os.path.join(toplevel_build, output_file)) as ninja_file:
+        ninja_file.write(ninja_output.getvalue())
+      ninja_output.close()
+      master_ninja.subninja(output_file)
+
     if target:
       if name != target.FinalOutput() and spec['toolset'] == 'target':
         target_short_names.setdefault(name, []).append(target)
       target_outputs[qualified_target] = target
       if qualified_target in all_targets:
         all_outputs.add(target.FinalOutput())
 
   if target_short_names:
     # Write a short name to build this target.  This benefits both the
     # "build chrome" case as well as the gyp tests, which expect to be
@@ skipping 48 matching lines @@
           arglists.append(
               (target_list, target_dicts, data, params, config_name))
         pool.map(CallGenerateOutputForConfig, arglists)
       except KeyboardInterrupt, e:
         pool.terminate()
         raise e
     else:
       for config_name in config_names:
         GenerateOutputForConfig(target_list, target_dicts, data, params,
                                 config_name)