Suggesting whole words only

The answer could be found here https://www.drupal.org/node/2091995
See comment #13

This definitely belongs into the DB backend's issue queue, yes. The Autocomplete module has no control over the suggestions that are displayed.
However, as noted in the other issue, I have no idea at all how this could happen. In the DB backend, only complete words should ever be present in the index, and only words from the index should appear as suggestions.

Can you maybe take a look into your database (table name search_api_db_INDEX_text) and see whether "som" or other incomplete words are present there?
Are you using the "Tokenizer" processor for your search index? If so, what is its configuration?

Ah, yes, thank you very much!
I now spotted the problem: it seems we didn't quite think of this in #1299238: Add option for partial matching and now, when you have enabled the "Search on parts of a word" option, you will also get incomplete words in your suggestions.
Once found, the bug was easy to fix: please see (and test) the attached patch.
(Would be great if we could add a test for this, but it would unfortunately be very hard to test the autocomplete functionality.)

This will also need to be ported to D8.

Thanks for testing, good to hear it works!

1. A result "siva" itself is not suggested - that is, without accompanying second word.

For "siva", the user can just press "Enter" – whether it's useful to still explicitly suggest it is at least debatable. In any case, it's a different issue.

2. I do not want the 2 words results at all.

Just disable "Suggest additional words" in the database server's autocomplete settings.

So, on the whole, this issue seems to be fixed with the provided patch? Then, if you have no further comments, I'll just commit it in the next days.

OK, committed.

As far as I know, there are no issues for the two feature requests you mention. (And the second one is by design, so they'd both be feature requests.)

Moving this issue to Search API 8.x so the patch can be ported.

D8 port of the patch #5

1. +++ b/search_api_db/src/Plugin/search_api/backend/Database.php
   @@ -1996,7 +1996,7 @@ class Database extends BackendPluginBase {
   +    $limit /= ceil(count($passes));
   

   I don't quite like that syntax. Is this something that is even allowed in Drupal core code standards? I mean. Could it ever divide itself by zero?

2. +++ b/search_api_db/src/Plugin/search_api/backend/Database.php
   @@ -2024,7 +2030,7 @@ class Database extends BackendPluginBase {
   +          return array();
   

   I can't see it here, but is the documentation updated to mention it can return an empty array?

Thanks a lot for the patch, Yannick, looks very good! It's really good to have help with porting all these old patches …

To address Nick's concerns:

I don't quite like that syntax. Is this something that is even allowed in Drupal core code standards? I mean. Could it ever divide itself by zero?

That's two entirely different questions. Is the syntax allowed? I wouldn't see why not. I think it's clear enough what it does, it's concise and I don't think making it more verbose would really increase readability.
But could that lead to a division by zero? Yes, yes it could. That's not the fault of the syntax, though, but of the logic. I'm putting in a check now. Thanks a lot for pointing this out!

However, the third question, which you've missed, is: Is this line complete and utter nonsense? Why, yes, yes it is! We of course want to apply ceil() to $limit after the division, not to the count (which is always an integer anyways) before.
So, fixed that, too (in the patch and with a quick commit in D7). Lucky you quoted that line and I spotted it this time.
(Just to be clear, this was in my D7 patch and commit already, so it's completely my own fault.)

I can't see it here, but is the documentation updated to mention it can return an empty array?

Since the search_api_autocomplete module doesn't even have a D8 branch yet, there isn't really a documentation per se. However, since it's perfectly possible that a successful search would also find no suggestions, it's of course legal to return an empty array.

Committed.
Thanks again!