make discussion module use MetadataOnlyEditingDescriptor which will not present a code edit region and only display the metadata editor

cms/templates/widgets/metadata-only-edit.html

@@ -0,0 +1 @@
+<%include file="metadata-edit.html" />

common/lib/xmodule/xmodule/discussion_module.py

@@ -3,6 +3,7 @@ from pkg_resources import resource_string, resource_listdir
 
 from xmodule.x_module import XModule
 from xmodule.raw_module import RawDescriptor
+from xmodule.editing_module import MetadataOnlyEditingDescriptor
 from xblock.core import String, Scope
 
 
@@ -28,7 +29,7 @@ class DiscussionModule(DiscussionFields, XModule):
         return self.system.render_template('discussion/_discussion_module.html', context)
 
 
-class DiscussionDescriptor(DiscussionFields, RawDescriptor):
+class DiscussionDescriptor(DiscussionFields, MetadataOnlyEditingDescriptor, RawDescriptor):
     module_class = DiscussionModule
     template_dir_name = "discussion"
 

common/lib/xmodule/xmodule/editing_module.py

@@ -40,6 +40,16 @@ class XMLEditingDescriptor(EditingDescriptor):
     js = {'coffee': [resource_string(__name__, 'js/src/raw/edit/xml.coffee')]}
     js_module_name = "XMLEditingDescriptor"
 
+class MetadataOnlyEditingDescriptor(EditingDescriptor):
+    """
+    Module that provides a raw editing view of its data as XML. It does not perform
+    any validation of its definition
+    """
+
+    js = {'coffee': [resource_string(__name__, 'js/src/raw/edit/metadata-only.coffee')]}
+    js_module_name = "MetadataOnlyEditingDescriptor"
+
+    mako_template = "widgets/metadata-only-edit.html"
 
 class JSONEditingDescriptor(EditingDescriptor):
     """

common/lib/xmodule/xmodule/js/src/raw/edit/metadata-only.coffee

@@ -0,0 +1,5 @@
+class @MetadataOnlyEditingDescriptor extends XModule.Descriptor
+  constructor: (@element) ->
+
+  save: ->
+    data: null

common/lib/xmodule/xmodule/raw_module.py

@@ -1,5 +1,5 @@
 from lxml import etree
-from xmodule.editing_module import XMLEditingDescriptor
+from xmodule.editing_module import XMLEditingDescriptor, MetadataOnlyEditingDescriptor
 from xmodule.xml_module import XmlDescriptor
 import logging
 import sys