+1 to the API function. But to the OP's point, I actually prefer that the symbol autocomplete is limited to just the current view. It would be really really overcrowded if every indexed symbol were in the autocomplete. Also, it wouldn't actually get you what you want, since many symbols are simply not indexed! Nearly all language definitions (by design) fail to index variables, for example, or functions that are not strictly public.
At the end of the day, Sublime is not an IDE. There are several plugins which provide this kind of semantic indexing functionality within Sublime (e.g. ENSIME for Scala), and they might serve you better than the vanilla editor.