Making the omni completer more robust

- There was a bug in not calling int() on the result of the first call to the
omnifunc.
- We need to be more resilient to badly written omnifuncs and check that the
result of the second call is a list or a dict with a list, as the vim docs say
the omnifunc should return on the second call.

One of the two fixes probably fixes #198 but since I can't repro the error, I
can't be sure.

python/completers/all/omni_completer.py

@@ -21,6 +21,10 @@ import vim
 import vimsupport
 from completers.completer import Completer
 
+OMNIFUNC_RETURNED_BAD_VALUE = 'Omnifunc returned bad value to YCM!'
+OMNIFUNC_NOT_LIST = ( 'Omnifunc did not return a list or a dict with a "words" '
+                     ' list when expected.' )
+
 class OmniCompleter( Completer ):
   def __init__( self ):
     super( OmniCompleter, self ).__init__()
@@ -43,20 +47,30 @@ class OmniCompleter( Completer ):
       self.stored_candidates = None
       return
 
-    return_value = vim.eval( self.omnifunc + '(1,"")' )
-    if return_value < 0:
+    try:
+      return_value = int( vim.eval( self.omnifunc + '(1,"")' ) )
+      if return_value < 0:
+        self.stored_candidates = None
+        return
+
+      omnifunc_call = [ self.omnifunc,
+                        "(0,'",
+                        vimsupport.EscapeForVim( query ),
+                        "')" ]
+
+      items = vim.eval( ''.join( omnifunc_call ) )
+      if hasattr( items, 'words' ):
+        items = items.words
+      if not hasattr( items, '__iter__' ):
+        raise TypeError( OMNIFUNC_NOT_LIST )
+
+      self.stored_candidates = filter( bool, items )
+    except (TypeError, ValueError) as error:
+      vimsupport.PostVimMessage(
+        OMNIFUNC_RETURNED_BAD_VALUE + ' ' + str( error ) )
       self.stored_candidates = None
       return
 
-    omnifunc_call = [ self.omnifunc,
-                      "(0,'",
-                      vimsupport.EscapeForVim( query ),
-                      "')" ]
-
-    items = vim.eval( ''.join( omnifunc_call ) )
-    if hasattr( items, 'words' ):
-      items = items.words
-    self.stored_candidates = filter( bool, items )
 
 
   def AsyncCandidateRequestReadyInner( self ):
@@ -68,5 +82,5 @@ class OmniCompleter( Completer ):
 
 
   def CandidatesFromStoredRequestInner( self ):
-    return self.stored_candidates
+    return self.stored_candidates if self.stored_candidates else []