Better triggering of semantic completion

Now there's a nice user-configurable setting for when YCM should trigger
semantic completion. This is very useful for the new omni_completer that uses
data coming from Vim's omnicomplete system.

plugin/youcompleteme.vim

@@ -95,6 +95,14 @@ let g:ycm_key_detailed_diagnostics =
 let g:ycm_global_ycm_extra_conf =
       \ get( g:, 'ycm_global_ycm_extra_conf', '' )
 
+let g:ycm_semantic_triggers =
+      \ get( g:, 'ycm_semantic_triggers', {
+      \   'c,cpp,objc,objcpp' : ['->', '.', '::'],
+      \   'perl,php' : ['->'],
+      \   'cs,java,javascript,d,vim,ruby,python,perl6,scala,vb' : ['.'],
+      \   'lua' : ['.', ':'],
+      \ } )
+
 " On-demand loading. Let's use the autoload folder and not slow down vim's
 " startup procedure.
 augroup youcompletemeStart

python/completers/all/omni_completer.py

@@ -32,19 +32,6 @@ class OmniCompleter( Completer ):
     return []
 
 
-  def ShouldUseNowInner( self, start_column ):
-    line = vim.current.line
-    previous_char_index = start_column - 1
-    if ( not len( line ) or
-        previous_char_index < 0 or
-        previous_char_index >= len( line ) ):
-      return False
-
-    if line[ previous_char_index ] == '.':
-      return True
-    return False
-
-
   def CandidatesForQueryAsyncInner( self, query ):
     if not self.omnifunc:
       self.stored_candidates = None

python/completers/completer.py

@@ -21,6 +21,7 @@ import abc
 import vim
 import vimsupport
 import ycm_core
+from collections import defaultdict
 
 
 class CompletionsCache( object ):
@@ -42,19 +43,43 @@ class Completer( object ):
 
 
   def __init__( self ):
+    self.triggers_for_filetype = TriggersForFiletype()
     self.completions_future = None
     self.completions_cache = None
 
 
   def ShouldUseNow( self, start_column ):
     inner_says_yes = self.ShouldUseNowInner( start_column )
+    if not inner_says_yes:
+      self.completions_cache = None
+
     previous_results_were_empty = ( self.completions_cache and
+                                    self.completions_cache.CacheValid() and
                                     not self.completions_cache.raw_completions )
     return inner_says_yes and not previous_results_were_empty
 
 
   def ShouldUseNowInner( self, start_column ):
-    pass
+    line = vim.current.line
+    line_length = len( line )
+    if not line_length or start_column - 1 >= line_length:
+      return False
+
+    filetype = vimsupport.CurrentFiletypes()[ 0 ]
+    triggers = self.triggers_for_filetype[ filetype ]
+
+    for trigger in triggers:
+      index = -1
+      trigger_length = len( trigger )
+      while True:
+        line_index = start_column + index
+        if line_index < 0 or line[ line_index ] != trigger[ index ]:
+          break
+
+        if abs( index ) == trigger_length:
+          return True
+        index -= 1
+    return False
 
 
   def CandidatesForQueryAsync( self, query ):
@@ -169,3 +194,16 @@ class Completer( object ):
 
   def DebugInfo( self ):
     return ''
+
+
+def TriggersForFiletype():
+  triggers = vim.eval( 'g:ycm_semantic_triggers' )
+  triggers_for_filetype = defaultdict( list )
+
+  for key, value in triggers.iteritems():
+    filetypes = key.split( ',' )
+    for filetype in filetypes:
+      triggers_for_filetype[ filetype ].extend( value )
+
+  return triggers_for_filetype
+

python/completers/cpp/clang_completer.py

@@ -199,7 +199,8 @@ class ClangCompleter( Completer ):
 
 
   def ShouldUseNow( self, start_column ):
-    return ShouldUseClang( start_column )
+    # We don't want to use the Completer API cache, we use one in the C++ code.
+    return self.ShouldUseNowInner( start_column )
 
 
   def DebugInfo( self ):
@@ -246,24 +247,3 @@ def DiagnosticsToDiagStructure( diagnostics ):
 def ClangAvailableForBuffer( buffer_object ):
   filetype = vim.eval( 'getbufvar({0}, "&ft")'.format( buffer_object.number ) )
   return filetype in CLANG_FILETYPES
-
-
-def ShouldUseClang( start_column ):
-  line = vim.current.line
-  previous_char_index = start_column - 1
-  if ( not len( line ) or
-       previous_char_index < 0 or
-       previous_char_index >= len( line ) ):
-    return False
-
-  if line[ previous_char_index ] == '.':
-    return True
-
-  if previous_char_index - 1 < 0:
-    return False
-
-  two_previous_chars = line[ previous_char_index - 1 : start_column ]
-  if ( two_previous_chars == '->' or two_previous_chars == '::' ):
-    return True
-
-  return False