Auto merge of #2750 - micbou:no-stderr-read, r=Valloric

[READY] Do not read server standard error

When the ycmd server crashes, we read its standard error and log the result. Unfortunately, this blocks Vim if a sub-server is still running after the crash (e.g. JediHTTP). In that case, the only way to unblock Vim is to manually kill the sub-server.

We could fix the issue by writing some (non-trivial) code that reads ycmd `stderr` without blocking but instead we simply don't read it at all. The drawback is small: [ycmd immediately redirects its `stdout` and `stderr` to logfiles at startup](ff255aed4a/ycmd/__main__.py (L150-L153)). In other words, reading its `stderr` is only useful if ycmd crashed before the redirection. This is something that should never happen.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/valloric/youcompleteme/2750)
<!-- Reviewable:end -->

python/ycm/tests/youcompleteme_test.py

@@ -50,7 +50,6 @@ def RunNotifyUserIfServerCrashed( ycm, test, post_vim_message ):
   ycm._logger = MagicMock( autospec = True )
   ycm._server_popen = MagicMock( autospec = True )
   ycm._server_popen.poll.return_value = test[ 'return_code' ]
-  ycm._server_popen.stderr.read.return_value = test[ 'stderr_output' ]
 
   ycm._NotifyUserIfServerCrashed()
 
@@ -69,7 +68,6 @@ def YouCompleteMe_NotifyUserIfServerCrashed_UnexpectedCore_test():
               "Use the ':YcmToggleLogs' command to check the logs." )
   RunNotifyUserIfServerCrashed( {
     'return_code': 3,
-    'stderr_output' : '',
     'expected_logs': [ message ],
     'expected_vim_message': message
   } )
@@ -81,7 +79,6 @@ def YouCompleteMe_NotifyUserIfServerCrashed_MissingCore_test():
               "using it. Follow the instructions in the documentation." )
   RunNotifyUserIfServerCrashed( {
     'return_code': 4,
-    'stderr_output': '',
     'expected_logs': [ message ],
     'expected_vim_message': message
   } )
@@ -94,7 +91,6 @@ def YouCompleteMe_NotifyUserIfServerCrashed_Python2Core_test():
               "interpreter path." )
   RunNotifyUserIfServerCrashed( {
     'return_code': 5,
-    'stderr_output': '',
     'expected_logs': [ message ],
     'expected_vim_message': message
   } )
@@ -107,7 +103,6 @@ def YouCompleteMe_NotifyUserIfServerCrashed_Python3Core_test():
               "interpreter path." )
   RunNotifyUserIfServerCrashed( {
     'return_code': 6,
-    'stderr_output': '',
     'expected_logs': [ message ],
     'expected_vim_message': message
   } )
@@ -119,7 +114,6 @@ def YouCompleteMe_NotifyUserIfServerCrashed_OutdatedCore_test():
               "install.py script. See the documentation for more details." )
   RunNotifyUserIfServerCrashed( {
     'return_code': 7,
-    'stderr_output': '',
     'expected_logs': [ message ],
     'expected_vim_message': message
   } )
@@ -131,11 +125,7 @@ def YouCompleteMe_NotifyUserIfServerCrashed_UnexpectedExitCode_test():
               "check the logs." )
   RunNotifyUserIfServerCrashed( {
     'return_code': 1,
-    'stderr_output': 'First line\r\n'
-                     'Second line',
-    'expected_logs': [ 'First line\n'
-                       'Second line',
-                       message ],
+    'expected_logs': [ message ],
     'expected_vim_message': message
   } )
 

python/ycm/youcompleteme.py

@@ -251,11 +251,6 @@ class YouCompleteMe( object ):
     else:
       error_message = EXIT_CODE_UNEXPECTED_MESSAGE.format( code = return_code )
 
-    server_stderr = '\n'.join(
-        utils.ToUnicode( self._server_popen.stderr.read() ).splitlines() )
-    if server_stderr:
-      self._logger.error( server_stderr )
-
     error_message = SERVER_SHUTDOWN_MESSAGE + ' ' + error_message
     self._logger.error( error_message )
     vimsupport.PostVimMessage( error_message )