Stephen Woods created SOLR-17322:
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Summary: Make RankQuery.getTopDocsCollector use covariant generic
types
Key: SOLR-17322
URL: https://issues.apache.org/jira/browse/SOLR-17322
Project: Solr
Issue Type: Bug
Security Level: Public (Default Security Level. Issues are Public)
Components: search
Affects Versions: 9.6.1, 9.6, 9.4.1, 9.5, 9.4, 9.2.1, 9.3, 9.1.1, 9.2, 9.1,
9.0
Reporter: Stephen Woods
Currently, rank queries can only use TopDocsCollectors that operate on
ScoreDocs.
TopDocsCollector has a class signature of:
{code:java}
public abstract class TopDocsCollector<T extends ScoreDoc> implements Collector
{code}
It contains a single covariant generic type T, which allows the collection of
not only ScoreDocs, but subclasses of ScoreDocs as well (in the event
additional information needs to be collected per document during the collection
process).
SOLR-15385 involved a large commit that removed raw types from much of the Solr
code base. As part of that work, RankQuery was modified so that the
getTopDocsCollector method no longer returns a raw TopDocsCollector but instead
returns a TopDocsCollector of invariant ScoreDocs. Unfortunately, by doing so,
it is no longer possible to use custom TopDocsCollectors that operate on types
that extend ScoreDoc in rank queries; they _only_ work with ScoreDocs.
The fix for this issue is very simple: Modify the method signature from:
{code:java}
public abstract TopDocsCollector<ScoreDoc> getTopDocsCollector(
int len, QueryCommand cmd, IndexSearcher searcher) throws IOException;
{code}
to
{code:java}
public abstract TopDocsCollector<? extends ScoreDoc> getTopDocsCollector(
int len, QueryCommand cmd, IndexSearcher searcher) throws IOException;
{code}
The call site for this method, within SolrIndexSearcher.buildTopDocsCollector,
already uses this type signature.
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