Do not depend on UltiSnips internals

Use UltiSnips#SnippetsInCurrentScope to fetch snippets.
Add an entry in the FAQ about the :UltiSnipsAddFiletypes command.

README.md

@@ -2648,6 +2648,16 @@ g:UltiSnipsJumpForwardTrigger
 g:UltiSnipsJumpBackwardTrigger
 ```
 
+### Snippets added with `:UltiSnipsAddFiletypes` do not appear in the popup menu
+
+For efficiency, YCM only fetches UltiSnips snippets in specific scenarios like
+visiting a buffer or setting its filetype. You can force YCM to retrieve them by
+manually triggering the `FileType` autocommand:
+
+```viml
+:doautocmd FileType
+```
+
 ### Why isn't YCM just written in plain VimScript, FFS?
 
 Because of the identifier completion engine and subsequence-based filtering.

doc/youcompleteme.txt

@@ -145,23 +145,24 @@ Contents ~
   19. YCM does not read identifiers from my tags files |youcompleteme-ycm-does-not-read-identifiers-from-my-tags-files|
   20. 'CTRL-U' in insert mode does not work                        |CTRL-sub-U|
   21. YCM conflicts with UltiSnips TAB key usage |youcompleteme-ycm-conflicts-with-ultisnips-tab-key-usage|
-  22. Why isn't YCM just written in plain VimScript, FFS? |youcompleteme-why-isnt-ycm-just-written-in-plain-vimscript-ffs|
-  23. Why does YCM demand such a recent version of Vim? |youcompleteme-why-does-ycm-demand-such-recent-version-of-vim|
-  24. I get annoying messages in Vim's status area when I type |youcompleteme-i-get-annoying-messages-in-vims-status-area-when-i-type|
-  25. Nasty bugs happen if I have the 'vim-autoclose' plugin installed |vim-sub-autoclose|
-  26. Is there some sort of YCM mailing list? I have questions |youcompleteme-is-there-sort-of-ycm-mailing-list-i-have-questions|
-  27. I get an internal compiler error when installing |youcompleteme-i-get-an-internal-compiler-error-when-installing|
-  28. I get weird errors when I press 'Ctrl-C' in Vim              |Ctrl-sub-C|
-  29. Why did YCM stop using Syntastic for diagnostics display? |youcompleteme-why-did-ycm-stop-using-syntastic-for-diagnostics-display|
-  30. Completion doesn't work with the C++ standard library headers |youcompleteme-completion-doesnt-work-with-c-standard-library-headers|
-  31. When I open a JavaScript file, I get an annoying warning about '.tern-project'
+  22. Snippets added with |:UltiSnipsAddFiletypes| do not appear in the popup menu
+  23. Why isn't YCM just written in plain VimScript, FFS? |youcompleteme-why-isnt-ycm-just-written-in-plain-vimscript-ffs|
+  24. Why does YCM demand such a recent version of Vim? |youcompleteme-why-does-ycm-demand-such-recent-version-of-vim|
+  25. I get annoying messages in Vim's status area when I type |youcompleteme-i-get-annoying-messages-in-vims-status-area-when-i-type|
+  26. Nasty bugs happen if I have the 'vim-autoclose' plugin installed |vim-sub-autoclose|
+  27. Is there some sort of YCM mailing list? I have questions |youcompleteme-is-there-sort-of-ycm-mailing-list-i-have-questions|
+  28. I get an internal compiler error when installing |youcompleteme-i-get-an-internal-compiler-error-when-installing|
+  29. I get weird errors when I press 'Ctrl-C' in Vim              |Ctrl-sub-C|
+  30. Why did YCM stop using Syntastic for diagnostics display? |youcompleteme-why-did-ycm-stop-using-syntastic-for-diagnostics-display|
+  31. Completion doesn't work with the C++ standard library headers |youcompleteme-completion-doesnt-work-with-c-standard-library-headers|
+  32. When I open a JavaScript file, I get an annoying warning about '.tern-project'
 file |.tern-sub-project|
-  32. When I start vim I get a runtime error saying 'R6034 An application has made an
+  33. When I start vim I get a runtime error saying 'R6034 An application has made an
 attempt to load the C runtime library incorrectly.' |R6034-An-application-has-made-an-attempt-to-load-the-C-runtime-library-incorrectly.|
-  33. I hear that YCM only supports Python 2, is that true? |youcompleteme-i-hear-that-ycm-only-supports-python-2-is-that-true|
-  34. On Windows I get "E887: Sorry, this command is disabled, the Python's site
+  34. I hear that YCM only supports Python 2, is that true? |youcompleteme-i-hear-that-ycm-only-supports-python-2-is-that-true|
+  35. On Windows I get "E887: Sorry, this command is disabled, the Python's site
 module could not be loaded" |E887:-Sorry-this-command-is-disabled-the-Python-s-site-module-could-not-be-loaded|
-  35. I can't complete python packages in a virtual environment. |youcompleteme-i-cant-complete-python-packages-in-virtual-environment.|
+  36. I can't complete python packages in a virtual environment. |youcompleteme-i-cant-complete-python-packages-in-virtual-environment.|
  12. Contributor Code of Conduct    |youcompleteme-contributor-code-of-conduct|
  13. Contact                                            |youcompleteme-contact|
  14. License                                            |youcompleteme-license|
@@ -2904,6 +2905,15 @@ options:
   g:UltiSnipsJumpForwardTrigger
   g:UltiSnipsJumpBackwardTrigger
 <
+-------------------------------------------------------------------------------
+Snippets added with *:UltiSnipsAddFiletypes* do not appear in the popup menu
+
+For efficiency, YCM only fetches UltiSnips snippets in specific scenarios like
+visiting a buffer or setting its filetype. You can force YCM to retrieve them
+by manually triggering the 'FileType' autocommand:
+>
+  :doautocmd FileType
+<
 -------------------------------------------------------------------------------
                *youcompleteme-why-isnt-ycm-just-written-in-plain-vimscript-ffs*
 Why isn't YCM just written in plain VimScript, FFS? ~

python/ycm/youcompleteme.py

@@ -51,12 +51,6 @@ from ycm.client.event_notification import ( SendEventNotificationAsync,
                                             EventNotification )
 from ycm.client.shutdown_request import SendShutdownRequest
 
-try:
-  from UltiSnips import UltiSnips_Manager
-  USE_ULTISNIPS_DATA = True
-except ImportError:
-  USE_ULTISNIPS_DATA = False
-
 
 def PatchNoProxy():
   current_value = os.environ.get('no_proxy', '')
@@ -319,7 +313,7 @@ class YouCompleteMe( object ):
     if not self.IsServerAlive():
       return
     extra_data = {}
-    _AddUltiSnipsDataIfNeeded( extra_data )
+    self._AddUltiSnipsDataIfNeeded( extra_data )
     SendEventNotificationAsync( 'BufferVisit', extra_data )
 
 
@@ -690,25 +684,16 @@ class YouCompleteMe( object ):
         extra_conf_vim_data )
 
 
-def _AddUltiSnipsDataIfNeeded( extra_data ):
-  if not USE_ULTISNIPS_DATA:
-    return
-
-  try:
-    # Since UltiSnips may run in a different python interpreter (python 3) than
-    # YCM, UltiSnips_Manager singleton is not necessary the same as the one
-    # used by YCM. In particular, it means that we cannot rely on UltiSnips to
-    # set the current filetypes to the singleton. We need to do it ourself.
-    UltiSnips_Manager.reset_buffer_filetypes()
-    UltiSnips_Manager.add_buffer_filetypes(
-      vimsupport.GetVariableValue( '&filetype' ) )
-    rawsnips = UltiSnips_Manager._snips( '', True )
-  except:
-    return
-
-  # UltiSnips_Manager._snips() returns a class instance where:
-  # class.trigger - name of snippet trigger word ( e.g. defn or testcase )
-  # class.description - description of the snippet
-  extra_data[ 'ultisnips_snippets' ] = [
-    { 'trigger': x.trigger, 'description': x.description } for x in rawsnips
-  ]
+  def _AddUltiSnipsDataIfNeeded( self, extra_data ):
+    # See :h UltiSnips#SnippetsInCurrentScope.
+    try:
+      vim.eval( 'UltiSnips#SnippetsInCurrentScope( 1 )' )
+    except vim.error:
+      return
+
+    snippets = vimsupport.GetVariableValue( 'g:current_ulti_dict_info' )
+    extra_data[ 'ultisnips_snippets' ] = [
+      { 'trigger': trigger,
+        'description': snippet[ 'description' ] }
+      for trigger, snippet in iteritems( snippets )
+    ]