Fix build when emma_coverage changes from false->true

build/android/gyp/emma_instr.py

 #!/usr/bin/env python
 #
 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Instruments classes and jar files.
 
 This script corresponds to the 'emma_instr' action in the java build process.
 Depending on whether emma_instrument is set, the 'emma_instr' action will either
@@ skipping 163 matching lines @@
            '-out', options.coverage_file,
            '-m', 'fullcopy']
     build_utils.CheckOutput(cmd)
 
     temp_jar_dir = os.path.join(temp_dir, 'lib')
     jars = os.listdir(temp_jar_dir)
     if len(jars) != 1:
       print('Error: multiple output files in: %s' % (temp_jar_dir))
       return 1
 
-    shutil.copy(os.path.join(temp_jar_dir, jars[0]), options.output_path)
+    # Delete output_path first to avoid modifying input_path in the case where
+    # input_path is a hardlink to output_path. http://crbug.com/571642

[jbudorick, 2015/12/22 19:34:44]

I'm confused about how this fixes 571642. That failure appears to appear at emma
time up at line 176?

[agrieve, 2015/12/22 20:10:00]

1. Build once without coverage enabled, and there's a GN copy() target with
src=input_path dst=output_path. This results in a hardlink
2. Build once with coverage enabled. It succeeds, but since output_path is the
same inode as input_path, writing to output_path actually causes input_path to
get updated as well (they still point to the same inode after this runs)
3. Build again, and emma complains that input_path is already instrumented
(since it was wrongly modified by the previous run)

[jbudorick, 2015/12/22 20:42:35]

ah, ok. lgtm

+    if os.path.exists(options.output_path):
+      os.unlink(options.output_path)
+    shutil.move(os.path.join(temp_jar_dir, jars[0]), options.output_path)
   finally:
     shutil.rmtree(temp_dir)
 
   if options.source_dirs:
     source_dirs = build_utils.ParseGypList(options.source_dirs)
   else:
     source_dirs = _GetSourceDirsFromSourceFiles(options.source_files)
   _CreateSourcesListFile(source_dirs, options.sources_list_file,
                          options.src_root)
 
@@ skipping 18 matching lines @@
 
 
 def main():
   option_parser = command_option_parser.CommandOptionParser(
       commands_dict=VALID_COMMANDS)
   command_option_parser.ParseAndExecute(option_parser)
 
 
 if __name__ == '__main__':
   sys.exit(main())