Check the server end point for available completer

Previously we were checking if the `hook.py` file existed for the given
filetype. ycmd has an endpoint for checking if given a filetype a
semantic completer is available. To avoid redundant requests we cache
those requests for every filetype. A semantic engine cannot be added
*after* the ycmd server is started so to avoid redundant requests we
cache those requests for every filetype and we clear the cache at server
setup, in this way if we issue a `YcmRestartServer` command the server
will be setup again and if a semantic completer is available we can use
it. Should fix #1284.

python/ycm/client/completer_available_request.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2013  Google Inc.
+#
+# This file is part of YouCompleteMe.
+#
+# YouCompleteMe is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# YouCompleteMe is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with YouCompleteMe.  If not, see <http://www.gnu.org/licenses/>.
+
+from ycm.client.base_request import ( BaseRequest, BuildRequestData,
+                                      HandleServerException )
+
+class CompleterAvailableRequest( BaseRequest ):
+  def __init__( self, filetypes ):
+    super( CompleterAvailableRequest, self ).__init__()
+    self.filetypes = filetypes
+    self._response = None
+
+
+  def Start( self ):
+    request_data = BuildRequestData()
+    request_data.update( { 'filetypes': self.filetypes } )
+    try:
+      self._response = self.PostDataToHandler( request_data,
+                                               'semantic_completion_available' )
+    except Exception as e:
+      HandleServerException( e )
+
+
+  def Response( self ):
+    return self._response
+
+
+def SendCompleterAvailableRequest( filetypes ):
+  request = CompleterAvailableRequest( filetypes )
+  # This is a blocking call.
+  request.Start()
+  return request.Response()

python/ycm/youcompleteme.py

@@ -30,9 +30,9 @@ from ycmd.request_wrap import RequestWrap
 from ycm.diagnostic_interface import DiagnosticInterface
 from ycm.omni_completer import OmniCompleter
 from ycm import syntax_parse
-from ycmd.completers.completer_utils import FiletypeCompleterExistsForFiletype
 from ycm.client.ycmd_keepalive import YcmdKeepalive
 from ycm.client.base_request import BaseRequest, BuildRequestData
+from ycm.client.completer_available_request import SendCompleterAvailableRequest
 from ycm.client.command_request import SendCommandRequest
 from ycm.client.completion_request import CompletionRequest
 from ycm.client.omni_completion_request import OmniCompletionRequest
@@ -98,6 +98,7 @@ class YouCompleteMe( object ):
     self._ycmd_keepalive.Start()
 
   def _SetupServer( self ):
+    self._available_completers = {}
     server_port = utils.GetUnusedLocalhostPort()
     # The temp options file is deleted by ycmd during startup
     with tempfile.NamedTemporaryFile( delete = False ) as options_file:
@@ -217,8 +218,20 @@ class YouCompleteMe( object ):
     return self._omnicomp
 
 
+  def FiletypeCompleterExistsForFiletype( self, filetype ):
+    try:
+      return self._available_completers[ filetype ]
+    except KeyError:
+      pass
+
+    exists_completer = ( self.IsServerAlive() and
+                         bool( SendCompleterAvailableRequest( filetype ) ) )
+    self._available_completers[ filetype ] = exists_completer
+    return exists_completer
+
+
   def NativeFiletypeCompletionAvailable( self ):
-    return any( [ FiletypeCompleterExistsForFiletype( x ) for x in
+    return any( [ self.FiletypeCompleterExistsForFiletype( x ) for x in
                   vimsupport.CurrentFiletypes() ] )