Fix for "lclose not allowed here" error on open

The problem was caused by a race condition of all things. ClangCompleter would
set possibly_completions_ready when starting the first parse pass for the file
and then would try to extract diagnostics for the file before the diagnostics
were done. Technically this was not a problem because only an empty diagnostics
vector would be returned, but this triggered Syntastic because hey, we have some
diagnostics to show (even though we don't).

And then Syntastic would try to close the location list window during startup
when this operation is not available. Technically it's Syntastic's fault, but a
more principled way to check for done diagnostics is to return and use a future
for file parsing operations and this solution also works around the Syntastic
issue.

autoload/youcompleteme.vim

@@ -108,8 +108,10 @@ endfunction
 
 
 function! s:OnCursorHold()
-  call s:OnFileReadyToParse()
+  " Order is important here; we need to extract any done diagnostics before
+  " reparsing the file again
   call s:UpdateDiagnosticNotifications()
+  call s:OnFileReadyToParse()
 endfunction
 
 

cpp/ycm/ClangCompleter.cpp

@@ -171,7 +171,7 @@ void ClangCompleter::UpdateTranslationUnit(
 }
 
 
-void ClangCompleter::UpdateTranslationUnitAsync(
+Future< void > ClangCompleter::UpdateTranslationUnitAsync(
     std::string filename,
     std::vector< UnsavedFile > unsaved_files,
     std::vector< std::string > flags )
@@ -186,8 +186,14 @@ void ClangCompleter::UpdateTranslationUnitAsync(
   shared_ptr< ClangPackagedTask > clang_packaged_task =
     make_shared< ClangPackagedTask >();
 
+  // TODO: vim hangs when we just open it and try to enter insert mode after the
+  // last '_' in ->parsing_task_ here
   clang_packaged_task->parsing_task_ = packaged_task< void >( functor );
+  unique_future< void > future =
+    clang_packaged_task->parsing_task_.get_future();
   clang_task_.Set( clang_packaged_task );
+
+  return Future< void >( boost::move( future ) );
 }
 
 

cpp/ycm/ClangCompleter.h

@@ -69,7 +69,7 @@ public:
 
   // NOTE: params are taken by value on purpose! With a C++11 compiler we can
   // avoid internal copies if params are taken by value (move ctors FTW)
-  void UpdateTranslationUnitAsync(
+  Future< void > UpdateTranslationUnitAsync(
       std::string filename,
       std::vector< UnsavedFile > unsaved_files,
       std::vector< std::string > flags );

cpp/ycm/ycm_core.cpp

@@ -67,6 +67,10 @@ BOOST_PYTHON_MODULE(ycm_core)
     .def( "ResultsReady", &Future< AsyncCompletions >::ResultsReady )
     .def( "GetResults", &Future< AsyncCompletions >::GetResults );
 
+  class_< Future< void > >( "FutureVoid" )
+    .def( "ResultsReady", &Future< void >::ResultsReady )
+    .def( "GetResults", &Future< void >::GetResults );
+
   class_< IdentifierCompleter, boost::noncopyable >( "IdentifierCompleter" )
     .def( "EnableThreading", &IdentifierCompleter::EnableThreading )
     .def( "AddCandidatesToDatabase",

python/completers/cpp/clang_completer.py

@@ -33,7 +33,7 @@ class ClangCompleter( Completer ):
     self.contents_holder = []
     self.filename_holder = []
     self.last_diagnostics = []
-    self.possibly_new_diagnostics = False
+    self.parse_future = None
     self.flags = Flags()
 
 
@@ -88,6 +88,7 @@ class ClangCompleter( Completer ):
     line, _ = vim.current.window.cursor
     column = int( vim.eval( "s:completion_start_column" ) ) + 1
     current_buffer = vim.current.buffer
+    # TODO: rename future to completions_future
     self.future = self.completer.CandidatesForQueryAndLocationInFileAsync(
       query,
       current_buffer.name,
@@ -110,26 +111,25 @@ class ClangCompleter( Completer ):
     if vimsupport.NumLinesInBuffer( vim.current.buffer ) < 5:
       return
 
-    self.possibly_new_diagnostics = True
-
     filename = vim.current.buffer.name
-    self.completer.UpdateTranslationUnitAsync(
+    self.parse_future = self.completer.UpdateTranslationUnitAsync(
       filename,
       self.GetUnsavedFilesVector(),
       self.flags.FlagsForFile( filename ) )
 
 
   def DiagnosticsForCurrentFileReady( self ):
-    return ( self.possibly_new_diagnostics and not
-             self.completer.UpdatingTranslationUnit( vim.current.buffer.name ) )
+    if not self.parse_future:
+      return False
 
+    return self.parse_future.ResultsReady()
 
   def GetDiagnosticsForCurrentFile( self ):
     if self.DiagnosticsForCurrentFileReady():
       self.last_diagnostics = [ DiagnosticToDict( x ) for x in
                                 self.completer.DiagnosticsForFile(
                                   vim.current.buffer.name ) ]
-      self.possibly_new_diagnostics = False
+      self.parse_future = None
     return self.last_diagnostics