Respect server support for didChangeWorkspaceFolders notification

ycmd/completers/language_server/language_server_completer.py

@@ -2148,11 +2148,14 @@ def _RefreshFileContentsUnderLock( self, file_name, contents, file_types ):
 
     if action == lsp.ServerFileState.OPEN_FILE:
       # First check if we need to inform the server of a new workspace.
-      workspace_for_file = self.GetWorkspaceForFilepath( file_name )
-      if workspace_for_file not in self._server_workspace_dirs:
-        self._server_workspace_dirs.add( workspace_for_file )
-        msg = lsp.DidChangeWorkspaceFolders( workspace_for_file )
-        self.GetConnection().SendNotification( msg )
+      # TODO: This check could be done once, after initialize response is
+      # received, and then saved in self._workspace_notification_supported.
+      if _ServerSupportsWorkspaceFoldersChangeNotif( self._server_capabilities )
+        workspace_for_file = self.GetWorkspaceForFilepath( file_name )
+        if workspace_for_file not in self._server_workspace_dirs:
+          self._server_workspace_dirs.add( workspace_for_file )
+          msg = lsp.DidChangeWorkspaceFolders( workspace_for_file )
+          self.GetConnection().SendNotification( msg )
 
       msg = lsp.DidOpenTextDocument( file_state, file_types, contents )
 
@@ -3590,6 +3593,12 @@ def DecodeModifiers( self, tokenModifiers ):
   return tokens
 
 
+def _ServerSupportsWorkspaceFoldersChangeNotif( server_capabilities ):
+  workspace = server_capabilities.get( 'workspace', {} )
+  workspace_folders = workspace.get( 'workspaceFolders', {} )
+  return _IsCapabilityProvided( workspace_folders, 'changeNotification' )
+
+
 def _IsCapabilityProvided( capabilities, query ):
   capability = capabilities.get( query )
   return bool( capability ) or capability == {}