Change GetBufferNumberForFilename default behavior

If no buffer exists for a given filename, the GetBufferNumberForFilename
function will create a buffer for that file by default. This behavior is
unexpected given the name of that function and may lead to performance issues
when ycmd returns diagnostics for a lot of files with no corresponding buffers.
The default behavior for that function should be to not create a buffer.

python/ycm/tests/vimsupport_test.py

@@ -797,8 +797,8 @@ def ReplaceChunks_SingleFile_Open_test( vim_command,
   #    raise a warning)
   #  - once whilst applying the changes
   get_buffer_number_for_filename.assert_has_exact_calls( [
-    call( single_buffer_name, False ),
-    call( single_buffer_name, False ),
+    call( single_buffer_name ),
+    call( single_buffer_name ),
   ] )
 
   # BufferIsVisible is called twice for the same reasons as above
@@ -895,9 +895,9 @@ def ReplaceChunks_SingleFile_NotOpen_test( vim_command,
   #  - once whilst applying the changes (-1 return)
   #  - finally after calling OpenFilename (1 return)
   get_buffer_number_for_filename.assert_has_exact_calls( [
-    call( single_buffer_name, False ),
-    call( single_buffer_name, False ),
-    call( single_buffer_name, False ),
+    call( single_buffer_name ),
+    call( single_buffer_name ),
+    call( single_buffer_name ),
   ] )
 
   # BufferIsVisible is called 3 times for the same reasons as above, with the
@@ -1007,7 +1007,7 @@ def ReplaceChunks_User_Declines_To_Open_File_test(
   #  - once to the check if we would require opening the file (so that we can
   #    raise a warning) (-1 return)
   get_buffer_number_for_filename.assert_has_exact_calls( [
-    call( single_buffer_name, False ),
+    call( single_buffer_name ),
   ] )
 
   # BufferIsVisible is called once for the above file, which wasn't visible.
@@ -1174,11 +1174,11 @@ def ReplaceChunks_MultiFile_Open_test( vim_command,
 
   # We checked for the right file names
   get_buffer_number_for_filename.assert_has_exact_calls( [
-    call( first_buffer_name, False ),
-    call( second_buffer_name, False ),
-    call( first_buffer_name, False ),
-    call( second_buffer_name, False ),
-    call( second_buffer_name, False ),
+    call( first_buffer_name ),
+    call( second_buffer_name ),
+    call( first_buffer_name ),
+    call( second_buffer_name ),
+    call( second_buffer_name ),
   ] )
 
   # We checked if it was OK to open the file

python/ycm/vimsupport.py

@@ -139,10 +139,10 @@ def GetUnsavedAndSpecifiedBufferData( including_filepath ):
   return buffers_data
 
 
-def GetBufferNumberForFilename( filename, open_file_if_needed = True ):
+def GetBufferNumberForFilename( filename, create_buffer_if_needed = False ):
   return GetIntValue( u"bufnr('{0}', {1})".format(
       EscapeForVim( os.path.realpath( filename ) ),
-      int( open_file_if_needed ) ) )
+      int( create_buffer_if_needed ) ) )
 
 
 def GetCurrentBufferFilepath():
@@ -328,7 +328,8 @@ def ConvertDiagnosticsToQfList( diagnostics ):
       text += ' (FixIt available)'
 
     return {
-      'bufnr' : GetBufferNumberForFilename( location[ 'filepath' ] ),
+      'bufnr' : GetBufferNumberForFilename( location[ 'filepath' ],
+                                            create_buffer_if_needed = True ),
       'lnum'  : line_num,
       'col'   : location[ 'column_num' ],
       'text'  : text,
@@ -641,7 +642,7 @@ def _GetNumNonVisibleFiles( file_list ):
   are not curerntly open in visible windows"""
   return len(
       [ f for f in file_list
-        if not BufferIsVisible( GetBufferNumberForFilename( f, False ) ) ] )
+        if not BufferIsVisible( GetBufferNumberForFilename( f ) ) ] )
 
 
 def _OpenFileInSplitIfNeeded( filepath ):
@@ -658,7 +659,7 @@ def _OpenFileInSplitIfNeeded( filepath ):
   not to open a file, or if opening fails, this method raises RuntimeError,
   otherwise, guarantees to return a visible buffer number in buffer_num."""
 
-  buffer_num = GetBufferNumberForFilename( filepath, False )
+  buffer_num = GetBufferNumberForFilename( filepath )
 
   # We only apply changes in the current tab page (i.e. "visible" windows).
   # Applying changes in tabs does not lead to a better user experience, as the
@@ -681,7 +682,7 @@ def _OpenFileInSplitIfNeeded( filepath ):
   # OpenFilename returns us to the original cursor location. This is what we
   # want, because we don't want to disorientate the user, but we do need to
   # know the (now open) buffer number for the filename
-  buffer_num = GetBufferNumberForFilename( filepath, False )
+  buffer_num = GetBufferNumberForFilename( filepath )
   if not BufferIsVisible( buffer_num ):
     # This happens, for example, if there is a swap file and the user
     # selects the "Quit" or "Abort" options. We just raise an exception to
@@ -959,16 +960,16 @@ def WriteToPreviewWindow( message ):
 
 def BufferIsVisibleForFilename( filename ):
   """Check if a buffer exists for a specific file."""
-  buffer_number = GetBufferNumberForFilename( filename, False )
+  buffer_number = GetBufferNumberForFilename( filename )
   return BufferIsVisible( buffer_number )
 
 
 def CloseBuffersForFilename( filename ):
   """Close all buffers for a specific file."""
-  buffer_number = GetBufferNumberForFilename( filename, False )
+  buffer_number = GetBufferNumberForFilename( filename )
   while buffer_number != -1:
     vim.command( 'silent! bwipeout! {0}'.format( buffer_number ) )
-    new_buffer_number = GetBufferNumberForFilename( filename, False )
+    new_buffer_number = GetBufferNumberForFilename( filename )
     if buffer_number == new_buffer_number:
       raise RuntimeError( "Buffer {0} for filename '{1}' should already be "
                           "wiped out.".format( buffer_number, filename ) )