This patch fixes the `goapp` local dev server to ignore GOPATH changes, the watching of which would otherwise yield the "There are too many files in your application for changes in all of them to be monitored" error.

mtime_file_watcher.py.patch

--- mtime_file_watcher.py	2017-01-20 11:36:51.000000000 -0500
+++ mtime_file_watcher.py.new	2017-01-20 11:37:24.000000000 -0500
@@ -139,6 +139,9 @@
     """
     filename_to_mtime = {}
     num_files = 0
+    gopath = os.environ["GOPATH"]+os.sep+"src"
+    if self._directory == gopath:
+          return filename_to_mtime
     for dirpath, dirnames, filenames in os.walk(self._directory,
                                                 followlinks=True):
       if self._quit_event.is_set():

Something like this should work:

curl https://gist.githubusercontent.com/saranrapjs/2219ff2db1105d46b179d3f697d6bd99/raw/99bb4d018712e3d658c6d8c56415bac2ee2da5e2/mtime_file_watcher.py.patch | patch $(dirname $(which goapp))/google/appengine/tools/devappserver2/mtime_file_watcher.py -