gn: More helpful default args file

tools/gn/command_args.cc

 // Copyright (c) 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.
 
 #include <stdio.h>
 #include <stdlib.h>
 
 #include <map>
 
 #include "base/command_line.h"
@@ skipping 225 matching lines @@
 
     // Ensure the file exists. Need to normalize path separators since on
     // Windows they can come out as forward slashes here, and that confuses some
     // of the commands.
     base::FilePath arg_file =
         setup.build_settings().GetFullPath(setup.GetBuildArgFile())
         .NormalizePathSeparators();
     if (!base::PathExists(arg_file)) {
       std::string argfile_default_contents =
           "# Build arguments go here. Examples:\n"
-          "#   enable_doom_melon = true\n"
-          "#   crazy_something = \"absolutely\"\n";
+          "#   is_component_build = true\n"
+          "#   is_debug = false\n"
+          "# See \"gn args --list\" for available build arguments.\n";

[scottmg, 2014/12/12 23:29:20]

I think this has to be "gn args out/gn --list".

[mdempsky, 2014/12/12 23:41:37]

I changed it to

  # See "gn args <dir_name> --list" for available build arguments.

to match "gn help args".

We could theoretically interpolate |build_dir| here, but I figure this is
simpler and avoids issues if a user specifies an absolute path (could result in
a really long command) or renames the build directory (the example file won't be
updated, and embedded directory name would become stale).

 #if defined(OS_WIN)
       // Use Windows lineendings for this file since it will often open in
       // Notepad which can't handle Unix ones.
       ReplaceSubstringsAfterOffset(&argfile_default_contents, 0, "\n", "\r\n");
 #endif
       base::CreateDirectory(arg_file.DirName());
       base::WriteFile(arg_file, argfile_default_contents.c_str(),
                       static_cast<int>(argfile_default_contents.size()));
     }
 
@@ skipping 78 matching lines @@
         "Or see \"gn help args\" for more variants.").PrintToStdout();
     return 1;
   }
 
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(kSwitchList))
     return ListArgs(args[0]);
   return EditArgsFile(args[0]);
 }
 
 }  // namespace commands