Make gyp_flag_compare.py regenerate and take a target name to make it more usable

tools/gn/bin/gyp_flag_compare.py

 #!/usr/bin/env python
 
 # Copyright 2014 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.
 
 """Given the output of -t commands from a ninja build for a gyp and GN generated
 build, report on differences between the command lines."""
 
 
+import os
+import subprocess
 import sys
 
 
 def FindAndRemoveArgWithValue(command_line, argname):
   """Given a command line as a list, remove and return the value of an option
   that takes a value as a separate entry.
 
   Modifies |command_line| in place.
   """
   if argname not in command_line:
@@ skipping 73 matching lines @@
     output += '  %s differ:\n' % name
     gyp_set = set(gyp[name]) - set(dont_care)
     gn_set = set(gn[name]) - set(dont_care)
     output += '    In gyp, but not in GN:\n      %s' % '\n      '.join(
         sorted(gyp_set - gn_set)) + '\n'
     output += '    In GN, but not in gyp:\n      %s' % '\n      '.join(
         sorted(gn_set - gyp_set)) + '\n\n'
   return output
 
 
+def Run(command_line):
+  """Run |command_line| as a subprocess and return stdout. Raises on error."""
+  return subprocess.check_output(command_line, shell=True)
+
+
 def main():
-  if len(sys.argv) != 3:
-    print 'usage: %s gyp_commands.txt gn_commands.txt' % __file__
+  if len(sys.argv) != 2 and len(sys.argv) != 3:
+    print 'usage: %s gyp_target gn_target' % __file__
+    print '   or: %s target' % __file__
     return 1
-  with open(sys.argv[1], 'rb') as f:
-    gyp = f.readlines()
-  with open(sys.argv[2], 'rb') as f:
-    gn = f.readlines()
-  all_gyp_flags = GetFlags(gyp)
-  all_gn_flags = GetFlags(gn)
+
+  if len(sys.argv) == 2:
+    sys.argv.append(sys.argv[1])
+
+  print >>sys.stderr, 'Regenerating...'
+  # Currently only Release, non-component.
+  Run('gn gen out/gn_flags --args="is_debug=false is_component_build=false"')
+  del os.environ['GYP_DEFINES']
+  Run('python build/gyp_chromium -Goutput_dir=out_gyp_flags -Gconfig=Release')
+  gn = Run('ninja -C out/gn_flags -t commands %s' % sys.argv[2])
+  gyp = Run('ninja -C out_gyp_flags/Release -t commands %s' % sys.argv[1])
+  all_gyp_flags = GetFlags(gyp.splitlines())
+  all_gn_flags = GetFlags(gn.splitlines())
   gyp_files = set(all_gyp_flags.keys())
   gn_files = set(all_gn_flags.keys())
   different_source_list = gyp_files != gn_files
   if different_source_list:
     print 'Different set of sources files:'
     print '  In gyp, not in GN:\n    %s' % '\n    '.join(
         sorted(gyp_files - gn_files))
     print '  In GN, not in gyp:\n    %s' % '\n    '.join(
         sorted(gn_files - gyp_files))
     print '\nNote that flags will only be compared for files in both sets.\n'
@@ skipping 18 matching lines @@
 
   for diff, files in files_with_given_differences.iteritems():
     print '\n'.join(sorted(files))
     print diff
 
   return 1 if files_with_given_differences or different_source_list else 0
 
 
 if __name__ == '__main__':
   sys.exit(main())