Was told to upstream this issue here.

Is your feature request about something that is currently impossible or hard to do? Please describe the problem.

'complete' is an option that specifies how ins-completion works in vim, more precisely the places that are going to be scanned when CTRL-N and CTRL-P are used. My proposal is to add another flag (set complete+=o), that would allow the user to receive the omnifunc completion items directly when pressing CTRL-N and CTRL-P, so that you wouldn't need to press CTRL-X CTRL-O. There is already similar support for scanning tags through the "t" or "]" flags.

Describe the solution you'd like
Omnifunc flag for 'complete' option (use case: set complete=o, set complete+=o)