Switch to standard coffee watcher

Using `ulimit -n` to set the limit much higher than the default of 256
in Darwin seems to avoid the `EMFILE` error that was plaguing our Mac
developers.

CHANGELOG.rst

@@ -5,6 +5,8 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+Common: Use coffee directly when watching for coffeescript file changes.
+
 Common: Make rake provide better error messages if packages are missing.
 
 Common: Repairs development documentation generation by sphinx.

doc/development.md

@@ -63,6 +63,25 @@ To get a full list of available rake tasks, use:
 
     rake -T
 
+### Troubleshooting
+
+#### Reference Error: XModule is not defined (javascript)
+This means that the javascript defining an xmodule hasn't loaded correctly. There are a number
+of different things that could be causing this:
+
+1. See `Error: watch EMFILE`
+
+#### Error: watch EMFILE (coffee)
+When running a development server, we also start a watcher process alongside to recompile coffeescript
+and sass as changes are made. On Mac OSX systems, the coffee watcher process takes more file handles
+than are allowed by default. This will result in `EMFILE` errors when coffeescript is running, and
+will prevent javascript from compiling, leading to the error 'XModule is not defined'
+
+To work around this issue, we use `Process::setrlimit` to set the number of allowed open files.
+Coffee watches both directories and files, so you will need to set this fairly high (anecdotally,
+8000 seems to do the trick on OSX 10.7.5, 10.8.3, and 10.8.4)
+
+
 ## Running Tests
 
 See `testing.md` for instructions on running the test suite.

rakelib/assets.rake

@@ -6,6 +6,8 @@ if USE_CUSTOM_THEME
     THEME_SASS = File.join(THEME_ROOT, "static", "sass")
 end
 
+MINIMAL_DARWIN_NOFILE_LIMIT = 8000
+
 def xmodule_cmd(watch=false, debug=false)
     xmodule_cmd = 'xmodule_assets common/static/xmodule'
     if watch
@@ -21,24 +23,14 @@ def xmodule_cmd(watch=false, debug=false)
 end
 
 def coffee_cmd(watch=false, debug=false)
-    if watch
-        # On OSx, coffee fails with EMFILE when
-        # trying to watch all of our coffee files at the same
-        # time.
-        #
-        # Ref: https://github.com/joyent/node/issues/2479
-        #
-        # So, instead, we use watchmedo, which works around the problem
-        "watchmedo shell-command " +
-                  "--command 'node_modules/.bin/coffee -c ${watch_src_path}' " +
-                  "--recursive " +
-                  "--patterns '*.coffee' " +
-                  "--ignore-directories " +
-                  "--wait " +
-                  "."
-    else
-        'node_modules/.bin/coffee --compile .'
+    if watch && Launchy::Application.new.host_os_family.darwin?
+        available_files = Process::getrlimit(:NOFILE)[0]
+        if available_files < MINIMAL_DARWIN_NOFILE_LIMIT
+            Process.setrlimit(:NOFILE, MINIMAL_DARWIN_NOFILE_LIMIT)
+
+        end
     end
+    "node_modules/.bin/coffee --compile #{watch ? '--watch' : ''} ."
 end
 
 def sass_cmd(watch=false, debug=false)