Provide script/gypi support for manifest generation

chrome/browser/resources/chromeos/chromevox/tools/generate_manifest.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.
+
+import json
+import io
+import optparse
+import os
+import sys
+
+'''Generate an extension manifest based on a template.'''
+
+
+def processJinjaTemplate(input_file, output_file, context):
+  jinja2_path = os.path.normpath(
+      os.path.join(os.path.abspath(__file__),
+                   *[os.path.pardir] * 7 + ['third_party/jinja2']))
+  sys.path.append(os.path.split(jinja2_path)[0])

[Peter Lundblad, 2014/05/23 16:04:27]

Why are you including a path component that you later discard?

[Peter Lundblad, 2014/05/23 16:04:27]

I recommend prepending so we pick up our own jinja2 in case it happens
to be available on the build system.  Also, would it be better to do
this at the top level to not have this function have the side effect of
modifying the global path (every time it gets called)?

[David Tseng, 2014/05/23 19:16:37]

Took this code from remoting; revised.

+  import jinja2
+  (template_path, template_name) = os.path.split(input_file)
+  env = jinja2.Environment(loader=jinja2.FileSystemLoader(template_path))
+  template = env.get_template(template_name)
+  rendered = template.render(context)
+  io.open(output_file, 'w', encoding='utf-8').write(rendered).close()

[Peter Lundblad, 2014/05/23 16:04:27]

nit: Why io.open?

[Peter Lundblad, 2014/05/23 16:04:27]

Ho would you feel about quickly loading the result into json to catch
syntax errors early.

also, split this line up and close the file on error.

[David Tseng, 2014/05/23 19:16:37]

Ditto; no I suspect it's because open doesn't let you specify encoding.

Also, 
"io module provides the Python interfaces to stream handling. Under Python 2.x,
this is proposed as an alternative to the built-in file object, but in Python
3.x it is the default interface to access files and streams."
from the python docs.

[David Tseng, 2014/05/23 19:16:37]

Sure. sgtm.

+
+
+def main():
+  parser = optparse.OptionParser(description=__doc__)
+  parser.usage = '%prog [options] <template_manifest_path>'
+  parser.add_option(
+      '-o', '--output_manifest', action='store', metavar='OUTPUT_MANIFEST',
+      help='File to place generated manifest')
+  parser.add_option(
+      '-g', '--is_guest_manifest', action='store', metavar='GUEST_MANIFEST',
+      help='Generate a guest mode capable manifest')
+
+  options, args = parser.parse_args()
+  if len(args) != 1:
+    print >>sys.stderr, 'Expected exactly one argument'
+    sys.exit(1)
+  processJinjaTemplate(args[0], options.output_manifest, parser.values.__dict__)

[Peter Lundblad, 2014/05/23 16:04:27]

What is parser.values.__dict__ for?

[David Tseng, 2014/05/23 19:16:37]

Allows us to pass the jinja2 "renderer" all options (e.g.
{ "is_guest_mode": 1})

without having to manually list everything.
If you know of a cleaner way to do this with OptPrase, I'm open to it.

+
+if __name__ == '__main__':
+  main()