Now can populate the loclist like Syntastic

plugin/youcompleteme.vim

@@ -129,6 +129,10 @@ let g:ycm_echo_current_diagnostic =
       \ get( g:, 'ycm_echo_current_diagnostic',
       \ get( g:, 'syntastic_echo_current_error', 1 ) )
 
+let g:ycm_always_populate_loc_list =
+      \ get( g:, 'ycm_always_populate_loc_list',
+      \ get( g:, 'syntastic_always_populate_loc_list', 0 ) )
+
 let g:ycm_error_symbol =
       \ get( g:, 'ycm_error_symbol',
       \ get( g:, 'syntastic_error_symbol', '>>' ) )

python/ycm/diagnostic_interface.py

@@ -47,11 +47,15 @@ class DiagnosticInterface( object ):
 
     if self._user_options[ 'enable_signs' ]:
       self._next_sign_id = _UpdateSigns( self._buffer_number_to_line_to_diags,
-                                        self._next_sign_id )
+                                         self._next_sign_id )
 
     if self._user_options[ 'enable_highlighting' ]:
       _UpdateSquiggles( self._buffer_number_to_line_to_diags )
 
+    if self._user_options[ 'always_populate_loc_list' ]:
+      vimsupport.SetLocationList(
+        vimsupport.ConvertDiagnosticsToQfList( diags ) )
+
 
   def _EchoDiagnosticForLine( self, line_num ):
     buffer_num = vim.current.buffer.number

python/ycm/vimsupport.py

@@ -147,6 +147,30 @@ def AddDiagnosticSyntaxMatch( line_num,
         group, line_num, column_num, line_end_num, column_end_num ) )
 
 
+def SetLocationList( diagnostics ):
+  """Diagnostics should be in qflist format; see ":h setqflist" for details."""
+  vim.eval( 'setloclist( 0, {0} )'.format( json.dumps( diagnostics ) ) )
+
+
+def ConvertDiagnosticsToQfList( diagnostics ):
+  def ConvertDiagnosticToQfFormat( diagnostic ):
+    # see :h getqflist for a description of the dictionary fields
+    # Note that, as usual, Vim is completely inconsistent about whether
+    # line/column numbers are 1 or 0 based in its various APIs. Here, it wants
+    # them to be 1-based.
+    location = diagnostic[ 'location' ]
+    return {
+      'bufnr' : GetBufferNumberForFilename( location[ 'filepath' ] ),
+      'lnum'  : location[ 'line_num' ] + 1,
+      'col'   : location[ 'column_num' ] + 1,
+      'text'  : diagnostic[ 'text' ],
+      'type'  : diagnostic[ 'kind' ],
+      'valid' : 1
+    }
+
+  return [ ConvertDiagnosticToQfFormat( x ) for x in diagnostics ]
+
+
 # Given a dict like {'a': 1}, loads it into Vim as if you ran 'let g:a = 1'
 # When |overwrite| is True, overwrites the existing value in Vim.
 def LoadDictIntoVimGlobals( new_globals, overwrite = True ):

python/ycm/youcompleteme.py

@@ -274,7 +274,7 @@ class YouCompleteMe( object ):
       # until the next request is created.
       self._latest_file_parse_request = None
       if qflist_format:
-        return [ _ConvertDiagnosticDataToVimData( x ) for x in diagnostics ]
+        return vimsupport.ConvertDiagnosticsToQfList( diagnostics )
       else:
         return diagnostics
     return []
@@ -379,17 +379,3 @@ def _AddUltiSnipsDataIfNeeded( extra_data ):
                                          } for x in rawsnips ]
 
 
-def _ConvertDiagnosticDataToVimData( diagnostic ):
-  # see :h getqflist for a description of the dictionary fields
-  # Note that, as usual, Vim is completely inconsistent about whether
-  # line/column numbers are 1 or 0 based in its various APIs. Here, it wants
-  # them to be 1-based.
-  location = diagnostic[ 'location' ]
-  return {
-    'bufnr' : vimsupport.GetBufferNumberForFilename( location[ 'filepath' ] ),
-    'lnum'  : location[ 'line_num' ] + 1,
-    'col'   : location[ 'column_num' ] + 1,
-    'text'  : diagnostic[ 'text' ],
-    'type'  : diagnostic[ 'kind' ],
-    'valid' : 1
-  }