Add error messages when ycmd crashed

Display an error message to the user depending on the status code
returned by the ycmd server.
Remove ycm_core checks in plugin/youcompleteme.vim. These checks are
now done by the ycmd server.
Do not start a separate process to check the core version but rely on
ycmd returning a specific exit code. This slightly improves the Vim
startup time.

plugin/youcompleteme.vim

@@ -42,43 +42,6 @@ elseif !has( 'python' ) && !has( 'python3' )
   finish
 endif
 
-let s:script_folder_path = escape( expand( '<sfile>:p:h' ), '\' )
-let s:python_folder_path = s:script_folder_path . '/../python/'
-let s:ycmd_folder_path = s:script_folder_path . '/../third_party/ycmd/'
-
-function! s:YcmLibsPresentIn( path_prefix )
-  if filereadable(a:path_prefix . 'ycm_core.so')
-    return 1
-  elseif filereadable(a:path_prefix . 'ycm_core.pyd')
-    return 1
-  elseif filereadable(a:path_prefix . 'ycm_core.dll')
-    return 1
-  endif
-  return 0
-endfunction
-
-if s:YcmLibsPresentIn( s:python_folder_path )
-  echohl WarningMsg |
-        \ echomsg "YCM libraries found in old YouCompleteMe/python location; " .
-        \ "please RECOMPILE YCM." |
-        \ echohl None
-  call s:restore_cpo()
-  finish
-endif
-
-let g:ycm_check_if_ycm_core_present =
-      \ get( g:, 'ycm_check_if_ycm_core_present', 1 )
-
-if g:ycm_check_if_ycm_core_present &&
-      \ !s:YcmLibsPresentIn( s:ycmd_folder_path )
-  echohl WarningMsg |
-        \ echomsg "ycm_core.[so|pyd|dll] not detected; you need to compile " .
-        \ "YCM before using it. Read the docs!" |
-        \ echohl None
-  call s:restore_cpo()
-  finish
-endif
-
 let g:loaded_youcompleteme = 1
 
 " NOTE: Most defaults are in third_party/ycmd/ycmd/default_settings.json. They

python/ycm/paths.py

@@ -133,7 +133,3 @@ def IsPythonVersionCorrect( path ):
 
 def PathToServerScript():
   return os.path.join( DIR_OF_YCMD, 'ycmd' )
-
-
-def PathToCheckCoreVersion():
-  return os.path.join( DIR_OF_YCMD, 'check_core_version.py' )

python/ycm/setup.py

@@ -42,18 +42,12 @@ def SetUpSystemPaths():
 
 
 def SetUpYCM():
-  from ycm import base, paths
-  from ycmd import user_options_store, utils
+  from ycm import base
+  from ycmd import user_options_store
   from ycm.youcompleteme import YouCompleteMe
 
   base.LoadJsonDefaultsIntoVim()
 
   user_options_store.SetAll( base.BuildServerConf() )
 
-  popen_args = [ paths.PathToPythonInterpreter(),
-                 paths.PathToCheckCoreVersion() ]
-
-  if utils.SafePopen( popen_args ).wait() == 2:
-    raise RuntimeError( 'YCM support libs too old, PLEASE RECOMPILE.' )
-
   return YouCompleteMe( user_options_store.GetAll() )

python/ycm/youcompleteme.py

@@ -34,7 +34,9 @@ from subprocess import PIPE
 from tempfile import NamedTemporaryFile
 from ycm import paths, vimsupport
 from ycmd import utils
+from ycmd import server_utils
 from ycmd.request_wrap import RequestWrap
+from ycmd.responses import ServerError
 from ycm.diagnostic_interface import DiagnosticInterface
 from ycm.omni_completer import OmniCompleter
 from ycm import syntax_parse
@@ -47,7 +49,6 @@ from ycm.client.completion_request import ( CompletionRequest,
 from ycm.client.omni_completion_request import OmniCompletionRequest
 from ycm.client.event_notification import ( SendEventNotificationAsync,
                                             EventNotification )
-from ycmd.responses import ServerError
 
 try:
   from UltiSnips import UltiSnips_Manager
@@ -77,13 +78,29 @@ PatchNoProxy()
 signal.signal( signal.SIGINT, signal.SIG_IGN )
 
 HMAC_SECRET_LENGTH = 16
-SERVER_CRASH_MESSAGE_STDERR_FILE = (
-  "The ycmd server SHUT DOWN (restart with ':YcmRestartServer'). "
+SERVER_SHUTDOWN_MESSAGE = (
+  "The ycmd server SHUT DOWN (restart with ':YcmRestartServer')." )
+STDERR_FILE_MESSAGE = (
   "Run ':YcmToggleLogs stderr' to check the logs." )
-SERVER_CRASH_MESSAGE_STDERR_FILE_DELETED = (
-  "The ycmd server SHUT DOWN (restart with ':YcmRestartServer'). "
+STDERR_FILE_DELETED_MESSAGE = (
   "Logfile was deleted; set 'g:ycm_server_keep_logfiles' to see errors "
   "in the future." )
+CORE_UNEXPECTED_MESSAGE = (
+  'Unexpected error while loading the YCM core library.' )
+CORE_MISSING_MESSAGE = (
+  'YCM core library not detected; you need to compile YCM before using it. '
+  'Follow the instructions in the documentation.' )
+CORE_PYTHON2_MESSAGE = (
+  "YCM core library compiled for Python 2 but loaded in Python 3. "
+  "Set the 'g:ycm_server_python_interpreter' option to a Python 2 "
+  "interpreter path." )
+CORE_PYTHON3_MESSAGE = (
+  "YCM core library compiled for Python 3 but loaded in Python 2. "
+  "Set the 'g:ycm_server_python_interpreter' option to a Python 3 "
+  "interpreter path." )
+CORE_OUTDATED_MESSAGE = (
+  'YCM core library too old; PLEASE RECOMPILE by running the install.py '
+  'script. See the documentation for more details.' )
 SERVER_IDLE_SUICIDE_SECONDS = 10800  # 3 hours
 DIAGNOSTIC_UI_FILETYPES = set( [ 'cpp', 'cs', 'c', 'objc', 'objcpp' ] )
 
@@ -159,11 +176,28 @@ class YouCompleteMe( object ):
     if self._user_notified_about_crash or self.IsServerAlive():
       return
     self._user_notified_about_crash = True
+
     try:
       vimsupport.CheckFilename( self._server_stderr )
-      vimsupport.PostVimMessage( SERVER_CRASH_MESSAGE_STDERR_FILE )
+      stderr_message = STDERR_FILE_MESSAGE
     except RuntimeError:
-      vimsupport.PostVimMessage( SERVER_CRASH_MESSAGE_STDERR_FILE_DELETED )
+      stderr_message = STDERR_FILE_DELETED_MESSAGE
+
+    message = SERVER_SHUTDOWN_MESSAGE
+    return_code = self._server_popen.poll()
+    if return_code == server_utils.CORE_UNEXPECTED_STATUS:
+      message += ' ' + CORE_UNEXPECTED_MESSAGE + ' ' + stderr_message
+    elif return_code == server_utils.CORE_MISSING_STATUS:
+      message += ' ' + CORE_MISSING_MESSAGE
+    elif return_code == server_utils.CORE_PYTHON2_STATUS:
+      message += ' ' + CORE_PYTHON2_MESSAGE
+    elif return_code == server_utils.CORE_PYTHON3_STATUS:
+      message += ' ' + CORE_PYTHON3_MESSAGE
+    elif return_code == server_utils.CORE_OUTDATED_STATUS:
+      message += ' ' + CORE_OUTDATED_MESSAGE
+    else:
+      message += ' ' + stderr_message
+    vimsupport.PostVimMessage( message )
 
 
   def ServerPid( self ):