[LUCENE-10539] Return a stream of completions from FSTCompletion

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 9.2
• Lucene Fields: New
• Assignee: Dawid Weiss
• Reporter: Dawid Weiss
• Created: 27/Apr/22 08:21
• Updated: 28/Aug/22 16:39
• Resolved: 29/Apr/22 19:47

Description

FSTLookup currently has a "num" parameter which limits the number of completions from the underlying automaton. But this has severe disadvantages if you need to collect completions that need to fulfill a secondary condition (for example, collect only verbs or terms that contain a certain infix). Then you can't determine the 'num' parameter easily because the number of filtered completions is unknown.

I also think implementation-wise it's also much nicer to provide a stream that iterates over completions rather than a fixed-size list. This allows for much more elegant code (stream.filter, stream.limit).

The provided patch adds a single Stream<Completion> lookup(key) method and modifies the existing lookup methods to use it.

Issue Links

• relates to: LUCENE-10540 Remove alphabetically ordered completions from FSTCompletion
• links to: GitHub Pull Request #844