Extra matching check when source defined as function in Typeahead

[verybadbug]

I use Typeahead with mysql database (LIKE query). So when I type "Sou Ca" php make query "WHERE (name LIKE '%Sou%') AND (name LIKE '%Ca%')", mysql return "South Carolina". In source function there are process(['South Carolina']). But nothing appear, because typeahead value and items in process not match.

I replace 'matcher', but want to make its default if 'source' is function.

[mdo]

Typeahead has been removed in v3, so punting on this.

[cvrebert]

Details of removal: #7805