Better handling of crashed ycmd; restart command

Previously the YCM Vim client would go bonkers when ycmd crashed. Now the user
can continue using Vim just without YCM functionality.

Also added a :YcmRestartServer command to let the user restart ycmd if it
crashed. With a little luck, this will be rarely necessary.

autoload/youcompleteme.vim

@@ -566,7 +566,11 @@ function! youcompleteme#Complete( findstart, base )
       return -2
     endif
 
-    return pyeval( 'ycm_state.CreateCompletionRequest().CompletionStartColumn()' )
+    py request = ycm_state.CreateCompletionRequest()
+    if !pyeval( 'bool(request)' )
+      return -2
+    endif
+    return pyeval( 'request.CompletionStartColumn()' )
   else
     return s:CompletionsForQuery( a:base )
   endif
@@ -584,6 +588,13 @@ function! youcompleteme#OmniComplete( findstart, base )
 endfunction
 
 
+function! s:RestartServer()
+  py ycm_state.RestartServer()
+endfunction
+
+command! YcmRestartServer call s:RestartServer()
+
+
 function! s:ShowDetailedDiagnostic()
   py ycm_state.ShowDetailedDiagnostic()
 endfunction

python/ycm/server/handlers.py

@@ -198,6 +198,7 @@ def _GetCompleterForRequestData( request_data ):
 
 @atexit.register
 def _ServerShutdown():
+  LOGGER.info( 'Server shutting down' )
   if SERVER_STATE:
     SERVER_STATE.Shutdown()
     extra_conf_store.Shutdown()

python/ycm/youcompleteme.py

@@ -88,12 +88,18 @@ class YouCompleteMe( object ):
             self._server_popen = subprocess.Popen( args,
                                                    stdout = fstdout,
                                                    stderr = fstderr )
-    self._CheckIfServerCrashed()
+    self._NotifyUserIfServerCrashed()
 
 
-  def _CheckIfServerCrashed( self ):
-    server_crashed = self._server_popen.poll()
-    if server_crashed:
+  def _IsServerAlive( self ):
+    returncode = self._server_popen.poll()
+    # When the process hasn't finished yet, poll() returns None.
+    return returncode is None
+
+
+  def _NotifyUserIfServerCrashed( self ):
+    if self._IsServerAlive():
+      return
     if self._server_stderr:
       with open( self._server_stderr, 'r' ) as server_stderr_file:
         vimsupport.PostMultiLineNotice( SERVER_CRASH_MESSAGE_STDERR_FILE +
@@ -102,6 +108,12 @@ class YouCompleteMe( object ):
         vimsupport.PostVimMessage( SERVER_CRASH_MESSAGE_SAME_STDERR )
 
 
+  def RestartServer( self ):
+    vimsupport.PostVimMessage( 'Restarting ycmd server...' )
+    self.OnVimLeave()
+    self._SetupServer()
+
+
   def CreateCompletionRequest( self, force_semantic = False ):
     # We have to store a reference to the newly created CompletionRequest
     # because VimScript can't store a reference to a Python object across
@@ -111,17 +123,23 @@ class YouCompleteMe( object ):
          self._omnicomp.ShouldUseNow() ):
       self._latest_completion_request = OmniCompletionRequest( self._omnicomp )
     else:
-      self._latest_completion_request = CompletionRequest( force_semantic )
+      self._latest_completion_request = ( CompletionRequest( force_semantic )
+                                          if self._IsServerAlive() else
+                                          None )
     return self._latest_completion_request
 
 
   def SendCommandRequest( self, arguments, completer ):
+    if self._IsServerAlive():
       return SendCommandRequest( arguments, completer )
 
 
   def GetDefinedSubcommands( self ):
+    if self._IsServerAlive():
       return BaseRequest.PostDataToHandler( BuildRequestData(),
                                             'defined_subcommands' )
+    else:
+      return []
 
 
   def GetCurrentCompletionRequest( self ):
@@ -143,9 +161,11 @@ class YouCompleteMe( object ):
 
 
   def OnFileReadyToParse( self ):
-    self._CheckIfServerCrashed()
     self._omnicomp.OnFileReadyToParse( None )
 
+    if not self._IsServerAlive():
+      self._NotifyUserIfServerCrashed()
+
     extra_data = {}
     if self._user_options[ 'collect_identifiers_from_tags_files' ]:
       extra_data[ 'tag_files' ] = _GetTagFiles()
@@ -159,26 +179,35 @@ class YouCompleteMe( object ):
 
 
   def OnBufferUnload( self, deleted_buffer_file ):
+    if not self._IsServerAlive():
+      return
     SendEventNotificationAsync( 'BufferUnload',
                                 { 'unloaded_buffer': deleted_buffer_file } )
 
 
   def OnBufferVisit( self ):
+    if not self._IsServerAlive():
+      return
     extra_data = {}
     _AddUltiSnipsDataIfNeeded( extra_data )
     SendEventNotificationAsync( 'BufferVisit', extra_data )
 
 
   def OnInsertLeave( self ):
+    if not self._IsServerAlive():
+      return
     SendEventNotificationAsync( 'InsertLeave' )
 
 
   def OnVimLeave( self ):
+    if self._IsServerAlive():
       self._server_popen.terminate()
     os.remove( self._temp_options_filename )
 
 
   def OnCurrentIdentifierFinished( self ):
+    if not self._IsServerAlive():
+      return
     SendEventNotificationAsync( 'CurrentIdentifierFinished' )
 
 
@@ -200,6 +229,8 @@ class YouCompleteMe( object ):
 
 
   def ShowDetailedDiagnostic( self ):
+    if not self._IsServerAlive():
+      return
     debug_info = BaseRequest.PostDataToHandler( BuildRequestData(),
                                                 'detailed_diagnostic' )
     if 'message' in debug_info:
@@ -207,8 +238,11 @@ class YouCompleteMe( object ):
 
 
   def DebugInfo( self ):
+    if self._IsServerAlive():
       debug_info = BaseRequest.PostDataToHandler( BuildRequestData(),
                                                   'debug_info' )
+    else:
+      debug_info = 'Server crashed, no debug info from server'
     debug_info += '\nServer running at: {0}'.format(
         BaseRequest.server_location )
     if self._server_stderr or self._server_stdout: