[SOLR-15030] Add score() function that returns the score of the current hit

solr/CHANGES.txt

@@ -17,6 +17,8 @@ New Features
 * SOLR-14414: Introduce a new, experimental Admin UI that can be used aside the current Admin UI. The new module is
   loaded together with the existing Admin UI and available under the URL path /solr/compose. (Christos Malliaridis)
 
+* SOLR-15030: Add score() function that returns the score of the current hit. The function can be used in pseudo-fields and post-filters. (Andrey Bozhko)
+
 Improvements
 ---------------------
 

solr/core/src/java/org/apache/solr/response/transform/ValueSourceAugmenter.java

@@ -25,6 +25,7 @@
 import org.apache.lucene.internal.hppc.IntObjectHashMap;
 import org.apache.lucene.queries.function.FunctionValues;
 import org.apache.lucene.queries.function.ValueSource;
+import org.apache.lucene.search.Scorable;
 import org.apache.solr.common.SolrDocument;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.response.ResultContext;
@@ -119,8 +120,13 @@ public void transform(SolrDocument doc, int docid, DocIterationInfo docIteration
       try {
         int idx = ReaderUtil.subIndex(docid, readerContexts);
         LeafReaderContext rcontext = readerContexts.get(idx);
-        FunctionValues values = valueSource.getValues(fcontext, rcontext);
         int localId = docid - rcontext.docBase;
+
+        if (context.wantsScores()) {
+          fcontext.put("scorer", new ScoreAndDoc(localId, docIterationInfo.score()));
+        }
+
+        FunctionValues values = valueSource.getValues(fcontext, rcontext);
         setValue(doc, values.objectVal(localId));
       } catch (IOException e) {
         throw new SolrException(
@@ -142,4 +148,24 @@ protected void setValue(SolrDocument doc, Object val) {
       doc.setField(name, val);
     }
   }
+
+  private static class ScoreAndDoc extends Scorable {
+    private final int docId;
+    private final float score;
+
+    ScoreAndDoc(int docId, float score) {
+      this.docId = docId;
+      this.score = score;
+    }
+
+    @Override
+    public int docID() {
+      return docId;
+    }
+
+    @Override
+    public float score() {
+      return score;
+    }
+  }
 }

solr/core/src/java/org/apache/solr/search/FunctionQParser.java

@@ -34,6 +34,7 @@
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.search.facet.AggValueSource;
 import org.apache.solr.search.function.FieldNameValueSource;
+import org.apache.solr.search.function.ScoreFunction;
 
 /**
  * Does "function query" parsing of function-call like strings, producing a {@link ValueSource}. As
@@ -515,6 +516,8 @@ protected ValueSource parseValueSource(int flags) throws SyntaxError {
           valueSource = ValueSourceParser.BoolConstValueSource.TRUE;
         } else if ("false".equals(id)) {
           valueSource = ValueSourceParser.BoolConstValueSource.FALSE;
+        } else if ("score".equals(id)) {
+          valueSource = ScoreFunction.INSTANCE;
         } else {
           if ((flags & FLAG_USE_FIELDNAME_SOURCE) != 0) {
             // Don't try to create a ValueSource for the field, just use a placeholder.

solr/core/src/java/org/apache/solr/search/FunctionRangeQuery.java

@@ -25,6 +25,7 @@
 import org.apache.lucene.queries.function.ValueSourceScorer;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.QueryVisitor;
+import org.apache.lucene.search.Scorable;
 import org.apache.lucene.search.ScoreMode;
 import org.apache.lucene.search.Weight;
 import org.apache.solr.common.SolrException;
@@ -68,6 +69,14 @@ class FunctionRangeCollector extends DelegatingCollector {
     public FunctionRangeCollector(Map<Object, Object> fcontext, Weight weight) {
       this.fcontext = fcontext;
       this.weight = weight;
+      // It would make sense to put this.scorer into the context,
+      // so that the context can be consumed in the call to
+      // doSetNextReader. But this.scorer is null, and will only be
+      // set at a later point by DelegatingCollector#setScorer
+      // (which happens *after* the call to doSetNextReader).
+      // So instead of using this.scorer directly, we wrap this collector
+      // as scorable - to work around the late initialization of this.scorer.
+      this.fcontext.put("scorer", new ScorableView(this));
     }
 
     @Override
@@ -113,4 +122,26 @@ public boolean equals(Object obj) {
   public int hashCode() {
     return 31 * classHash() + rangeFilt.hashCode();
   }
+
+  private static class ScorableView extends Scorable {
+    private final DelegatingCollector collector;
+
+    ScorableView(DelegatingCollector collector) {
+      this.collector = collector;
+    }
+
+    @Override
+    public float score() throws IOException {
+      assert collector.scorer != null
+          : "scorer must first be set via DelegatingCollector#setScorer";
+      return collector.scorer.score();
+    }
+
+    @Override
+    public int docID() {
+      assert collector.scorer != null
+          : "scorer must first be set via DelegatingCollector#setScorer";
+      return collector.scorer.docID();
+    }
+  }
 }

solr/core/src/java/org/apache/solr/search/SolrReturnFields.java

@@ -59,7 +59,7 @@ public class SolrReturnFields extends ReturnFields {
 
   // Field names that are OK to include in the response.
   // This will include pseudo fields, lucene fields, and matching globs
-  private Set<String> okFieldNames = new HashSet<>();
+  private final Set<String> okFieldNames = new HashSet<>();
 
   // The list of explicitly requested fields
   // Order is important for CSVResponseWriter
@@ -515,6 +515,12 @@ private void addField(
       String disp = (key == null) ? field : key;
       augmenters.addTransformer(new ScoreAugmenter(disp));
       scoreDependentFields.put(disp, disp.equals(SCORE) ? "" : SCORE);
+    } else if (key != null && isPseudoField) {
+      // SOLR-15030: a pseudo-field based on the function query may need scores,
+      // so we consider all pseudo-fields as potentially requiring scores.
+      // At the same time, we don't set _wantScore = true because the field
+      // list must explicitly include 'score' field to enable scores
+      scoreDependentFields.put(key, "");
     }
   }
 
@@ -576,7 +582,7 @@ public boolean wantsScore() {
 
   @Override
   public Map<String, String> getScoreDependentReturnFields() {
-    return scoreDependentFields;
+    return _wantsScore ? scoreDependentFields : Map.of();
   }
 
   @Override

solr/core/src/java/org/apache/solr/search/function/ScoreFunction.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.search.function;
+
+import java.io.IOException;
+import java.util.Map;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.queries.function.FunctionValues;
+import org.apache.lucene.queries.function.ValueSource;
+import org.apache.lucene.queries.function.docvalues.FloatDocValues;
+import org.apache.lucene.search.Scorable;
+import org.apache.solr.common.SolrException;
+
+/** Returns the score of the current hit. */
+public final class ScoreFunction extends ValueSource {
+
+  public static final ScoreFunction INSTANCE = new ScoreFunction();
+
+  @Override
+  public FunctionValues getValues(Map<Object, Object> context, LeafReaderContext readerContext)
+      throws IOException {
+    Scorable scorer = (Scorable) context.get("scorer");
+    if (scorer == null) {
+      throw new SolrException(
+          SolrException.ErrorCode.BAD_REQUEST, "score function cannot access the document scores");
+    }
+
+    return new FloatDocValues(this) {
+      @Override
+      public float floatVal(int doc) throws IOException {
+        assert scorer.docID() == doc
+            : "Expected scorer to be positioned on doc: " + doc + ", but was: " + scorer.docID();
+        return scorer.score();
+      }
+
+      @Override
+      public boolean exists(int doc) {
+        assert scorer.docID() == doc
+            : "Expected scorer to be positioned on doc: " + doc + ", but was: " + scorer.docID();
+        return true;
+      }
+    };
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    return o instanceof ScoreFunction;
+  }
+
+  @Override
+  public int hashCode() {
+    return getClass().hashCode();
+  }
+
+  @Override
+  public String description() {
+    return "score";
+  }
+}

solr/core/src/test/org/apache/solr/search/QueryEqualityTest.java

@@ -858,6 +858,10 @@ public void testFuncCscore() throws Exception {
     assertFuncEquals("cscore()", "cscore(  )");
   }
 
+  public void testFuncScore() throws Exception {
+    assertFuncEquals("score", "score  ");
+  }
+
   public void testFuncTop() throws Exception {
     assertFuncEquals("top(sum(3,foo_i))");
   }