[LUCENE-8330] Detach IndexWriter from MergePolicy

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 7.4, 8.0
• Fix Version/s: 7.4, 8.0
• Lucene Fields: New, Patch Available
• Assignee: Simon Willnauer
• Reporter: Simon Willnauer
• Created: 24/May/18 12:04
• Updated: 28/Aug/22 15:30
• Resolved: 07/Jun/18 09:43

Description

This change introduces a new MergePolicy.MergeContext interface
that is easy to mock and cuts over all instances of IW to MergeContext.
Since IW now implements MergeContext the cut over is straight forward.
This reduces the exposed API available in MP dramatically and allows
efficient testing without relying on IW to improve the coverage and
testability of our MP implementations.