Switch MB to write the GN args to args.gn.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index 1733618715f902660811de782e5601698628c86d..cdf1cc3d46b4b44de7a3e8db6090df0df45b9cd9 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -27,6 +27,13 @@ import urllib2
 
 from collections import OrderedDict
 
+CHROMIUM_SRC_DIR = os.path.dirname(os.path.dirname(os.path.dirname(
+    os.path.abspath(__file__))))
+sys.path = [os.path.join(CHROMIUM_SRC_DIR, 'build')] + sys.path
+
+import gn_helpers
+
+
 def main(args):
   mbw = MetaBuildWrapper()
   return mbw.Main(args)
@@ -34,11 +41,9 @@ def main(args):
 
 class MetaBuildWrapper(object):
   def __init__(self):
-    p = os.path
-    d = os.path.dirname
-    self.chromium_src_dir = p.normpath(d(d(d(p.abspath(__file__)))))
-    self.default_config = p.join(self.chromium_src_dir, 'tools', 'mb',
-                                 'mb_config.pyl')
+    self.chromium_src_dir = CHROMIUM_SRC_DIR
+    self.default_config = os.path.join(self.chromium_src_dir, 'tools', 'mb',
+                                       'mb_config.pyl')
     self.executable = sys.executable
     self.platform = sys.platform
     self.sep = os.sep
@@ -255,7 +260,9 @@ class MetaBuildWrapper(object):
   def CmdLookup(self):
     vals = self.Lookup()
     if vals['type'] == 'gn':
-      cmd = self.GNCmd('gen', '_path_', vals['gn_args'])
+      cmd = self.GNCmd('gen', '_path_')
+      gn_args = self.GNArgs(vals)
+      self.Print('\nWriting """\\\n%s""" to _path_/args.gn.\n' % gn_args)
       env = None
     else:
       cmd, env = self.GYPCmd('_path_', vals)
@@ -690,7 +697,14 @@ class MetaBuildWrapper(object):
   def RunGNGen(self, vals):
     build_dir = self.args.path[0]
 
-    cmd = self.GNCmd('gen', build_dir, vals['gn_args'], extra_args=['--check'])
+    cmd = self.GNCmd('gen', build_dir, '--check')
+    gn_args = self.GNArgs(vals)
+
+    # Since GN hasn't run yet, the build directory may not even exist.
+    self.MaybeMakeDirectory(self.ToAbsPath(build_dir))
+
+    gn_args_path = self.ToAbsPath(build_dir, 'args.gn')
+    self.WriteFile(gn_args_path, gn_args)
 
     swarming_targets = []
     if getattr(self.args, 'swarming_targets_file', None):
@@ -722,10 +736,6 @@ class MetaBuildWrapper(object):
                       ('//testing/buildbot/gn_isolate_map.pyl', err))
 
       gn_runtime_deps_path = self.ToAbsPath(build_dir, 'runtime_deps')
-
-      # Since GN hasn't run yet, the build directory may not even exist.
-      self.MaybeMakeDirectory(self.ToAbsPath(build_dir))
-
       self.WriteFile(gn_runtime_deps_path, '\n'.join(gn_labels) + '\n')
       cmd.append('--runtime-deps-list-file=%s' % gn_runtime_deps_path)
 
@@ -792,7 +802,7 @@ class MetaBuildWrapper(object):
     command, extra_files = self.GetIsolateCommand(target, vals, gn_isolate_map)
 
     label = gn_isolate_map[target_name]['label']
-    cmd = self.GNCmd('desc', build_dir, extra_args=[label, 'runtime_deps'])
+    cmd = self.GNCmd('desc', build_dir, label, 'runtime_deps')
     ret, out, _ = self.Call(cmd)
     if ret:
       if out:
@@ -841,23 +851,29 @@ class MetaBuildWrapper(object):
       isolate_path + 'd.gen.json',
     )
 
-  def GNCmd(self, subcommand, path, gn_args='', extra_args=None):
+  def GNCmd(self, subcommand, path, *args):
     if self.platform == 'linux2':
       subdir, exe = 'linux64', 'gn'
     elif self.platform == 'darwin':
       subdir, exe = 'mac', 'gn'
     else:
       subdir, exe = 'win', 'gn.exe'
+
     gn_path = self.PathJoin(self.chromium_src_dir, 'buildtools', subdir, exe)
 
-    cmd = [gn_path, subcommand, path]
+    return [gn_path, subcommand, path] + list(args)
+
+  def GNArgs(self, vals):
+    gn_args = vals['gn_args']
     if self.args.goma_dir:
       gn_args += ' goma_dir="%s"' % self.args.goma_dir
-    if gn_args:
-      cmd.append('--args=%s' % gn_args)
-    if extra_args:
-      cmd.extend(extra_args)
-    return cmd
+
+    # Canonicalize the arg string into a sorted, newline-separated list
+    # of key-value pairs, and de-dup the keys if need be so that only
+    # the last instance of each arg is listed.
+    gn_args = gn_helpers.ToGNString(gn_helpers.FromGNArgs(gn_args))
+
+    return gn_args
 
   def RunGYPGen(self, vals):
     path = self.args.path[0]
@@ -1086,8 +1102,11 @@ class MetaBuildWrapper(object):
 
     matching_targets = set()
     try:
-      cmd = self.GNCmd('refs', self.args.path[0]) + [
-          '@%s' % response_file.name, '--all', '--as=output']
+      cmd = self.GNCmd('refs',
+                       self.args.path[0],
+                       '@%s' % response_file.name,
+                       '--all',
+                       '--as=output')
       ret, out, _ = self.Run(cmd, force_verbose=False)
       if ret and not 'The input matches no targets' in out:
         self.WriteFailureAndRaise('gn refs returned %d: %s' % (ret, out),
@@ -1098,8 +1117,10 @@ class MetaBuildWrapper(object):
         if build_output in targets:
           matching_targets.add(build_output)
 
-      cmd = self.GNCmd('refs', self.args.path[0]) + [
-          '@%s' % response_file.name, '--all']
+      cmd = self.GNCmd('refs',
+                       self.args.path[0],
+                       '@%s' % response_file.name,
+                       '--all')
       ret, out, _ = self.Run(cmd, force_verbose=False)
       if ret and not 'The input matches no targets' in out:
         self.WriteFailureAndRaise('gn refs returned %d: %s' % (ret, out),