Hi, I am working on getting Solr upgraded to Lucene 9.8 [0] and I wanted to raise visibility on an issue I ran into.
I believe PR#12380 [1] introduced a change that calls `finish()` on the LeafCollector [2]. The trouble is on Solr side we have a few collectors that extend SimpleCollector. (to be more precise there is a DelegatingCollector in between but that does not change things). SimpleCollector returns `this` on the `getLeafCollector` call, so now there are 2 calls to the `finish()` method on the same collector instance (one as a leaf, one at the end). One example I am working with is CollapsingQParserPlugin$OrdScoreCollector [3] where I am seeing a few tests fail because calling `finish` twice will mess up the results. I don't know yet if there are others. My first question is to validate this analysis with someone that knows this code (and perhaps the Solr code too), and ideally also take a quick look at my fix [4]. Second is related to PR#12380. is it expected that the 'finish' method is idempotent? per my tests this seems to be called twice now in some cases and it will be the case for any implementation extending SimpleCollector. also given that SimpleCollector's getLeafCollector method is final, there is almost no room for passing some state wrt. this being a leaf vs not. thanks, alex [0] https://github.com/apache/solr/pull/1958 [1] https://github.com/apache/lucene/pull/12380 [2] https://github.com/apache/lucene/blob/releases/lucene/9.8.0/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java#L779 [3] https://github.com/apache/solr/blob/f0fcd300c896b858ae83235ecdb0a109eaea5cea/solr/core/src/java/org/apache/solr/search/CollapsingQParserPlugin.java#L594 [4] https://github.com/apache/solr/commit/fc8a2ffe8951f31aa3b65fac2adc9eaa3fee6258
