[LUCENE-5152] Lucene FST is not immutable

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 4.4
• Fix Version/s: 4.5, 6.0
• Component/s: core/FSTs
• Lucene Fields: New, Patch Available
• Assignee: Unassigned
• Reporter: Simon Willnauer
• Created: 30/Jul/13 14:04
• Updated: 28/Aug/22 13:51
• Resolved: 12/Sep/13 13:55

Description

a spinnoff from LUCENE-5120 where the analyzing suggester modified a returned output from and FST (BytesRef) which caused sideffects in later execution.

I added an assertion into the FST that checks if a cached root arc is modified and in-fact this happens for instance in our MemoryPostingsFormat and I bet we find more places. We need to think about how to make this less trappy since it can cause bugs that are super hard to find.