[LUCENE-6271] PostingsEnum should have consistent flags behavior

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 5.1
• Lucene Fields: New
• Assignee: Robert Muir
• Reporter: Ryan Ernst
• Created: 20/Feb/15 19:15
• Updated: 28/Aug/22 14:26
• Resolved: 04/Apr/15 01:56

Description

When asking for flags like OFFSETS or PAYLOADS with DocsAndPositionsEnum, the behavior was to always return an enum, even if offsets or payloads were not indexed. They would just not be available from the enum if they were not present. This behavior was carried over to PostingsEnum, which is good.

However, the new POSITIONS flag has different behavior. If positions are not available, null is returned, instead of a PostingsEnum that just gives access to freqs. This behavior is confusing, as it means you have to special case asking for positions (only ask if you know they were indexed) which sort of defeats the purpose of the unified PostingsEnum.

We should make POSITIONS have the same behavior as other flags. The trickiest part will be maintaining backcompat for DocsAndPositionsEnum in 5.x, but I think it can be done.