LUCENE-8949: Allow LeafFieldComparators to publish Feature Values

lucene/core/src/java/org/apache/lucene/document/FeatureSortField.java

@@ -160,5 +160,10 @@ public Float value(int slot) {
     public int compareTop(int doc) throws IOException {
       return Float.compare(topValue, getValueForDoc(doc));
     }
+
+    @Override
+    public Float leafValue(int docID) throws IOException {
+      return getValueForDoc(docID);
+    }
   }
 }

lucene/core/src/java/org/apache/lucene/document/LatLonPointDistanceComparator.java

@@ -217,6 +217,12 @@ public int compareTop(int doc) throws IOException {
     return minValue;
   }
 
+  //TODO: Implement this
+  @Override
+  public Double leafValue(int docID) throws IOException {
+    throw new UnsupportedOperationException("This comparator does not support getting leaf values");
+  }
+
   // second half of the haversin calculation, used to convert results from haversin1 (used internally
   // for sorting) for display purposes.
   static double haversin2(double partial) {

lucene/core/src/java/org/apache/lucene/search/FieldComparator.java

@@ -219,6 +219,11 @@ public Double value(int slot) {
     public int compareTop(int doc) throws IOException {
       return Double.compare(topValue, getValueForDoc(doc));
     }
+
+    @Override
+    public Double leafValue(int docID) throws IOException {
+      return getValueForDoc(docID);
+    }
   }
 
   /** Parses field's values as float (using {@link
@@ -279,6 +284,11 @@ public Float value(int slot) {
     public int compareTop(int doc) throws IOException {
       return Float.compare(topValue, getValueForDoc(doc));
     }
+
+    @Override
+    public Float leafValue(int docID) throws IOException {
+      return getValueForDoc(docID);
+    }
   }
 
   /** Parses field's values as int (using {@link
@@ -341,6 +351,11 @@ public Integer value(int slot) {
     public int compareTop(int doc) throws IOException {
       return Integer.compare(topValue, getValueForDoc(doc));
     }
+
+    @Override
+    public Integer leafValue(int docID) throws IOException {
+      return getValueForDoc(docID);
+    }
   }
 
   /** Parses field's values as long (using {@link
@@ -401,6 +416,11 @@ public Long value(int slot) {
     public int compareTop(int doc) throws IOException {
       return Long.compare(topValue, getValueForDoc(doc));
     }
+
+    @Override
+    public Long leafValue(int docID) throws IOException {
+      return getValueForDoc(docID);
+    }
   }
 
   /** Sorts by descending relevance.  NOTE: if you are
@@ -484,6 +504,11 @@ public int compareTop(int doc) throws IOException {
       assert !Float.isNaN(docValue);
       return Float.compare(docValue, topValue);
     }
+
+    @Override
+    public Float leafValue(int docID) throws IOException {
+      return scorer.score();
+    }
   }
 
   /** Sorts by ascending docID */
@@ -545,6 +570,11 @@ public int compareTop(int doc) {
       return Integer.compare(topValue, docValue);
     }
 
+    @Override
+    public Integer leafValue(int docID) throws IOException {
+      return docBase + docID;
+    }
+
     @Override
     public void setScorer(Scorable scorer) {}
   }
@@ -686,6 +716,11 @@ public int compareBottom(int doc) throws IOException {
       }
     }
 
+    @Override
+    public Integer leafValue(int docID) throws IOException {
+      return getOrdForDoc(docID);
+    }
+
     @Override
     public void copy(int slot, int doc) throws IOException {
       int ord = getOrdForDoc(doc);
@@ -927,5 +962,10 @@ public int compareTop(int doc) throws IOException {
 
     @Override
     public void setScorer(Scorable scorer) {}
+
+    @Override
+    public BytesRef leafValue(int docID) throws IOException {
+      return getValueForDoc(docID);
+    }
   }
 }

lucene/core/src/java/org/apache/lucene/search/LeafFieldComparator.java

@@ -51,7 +51,7 @@
  * @see FieldComparator
  * @lucene.experimental
  */
-public interface LeafFieldComparator {
+public interface LeafFieldComparator<T> {
 
   /**
    * Set the bottom slot, ie the "weakest" (sorted last)
@@ -116,4 +116,7 @@ public interface LeafFieldComparator {
    * obtain the current hit's score, if necessary. */
   void setScorer(Scorable scorer) throws IOException;
 
+  /** Publishes feature values for the given docID
+   */
+  T leafValue(int doc) throws IOException;
 }

lucene/core/src/java/org/apache/lucene/search/MultiLeafFieldComparator.java

@@ -89,4 +89,15 @@ public void setScorer(Scorable scorer) throws IOException {
     }
   }
 
+  @Override
+  public Object leafValue(int docID) throws IOException {
+    Object[] valuesArray = new Object[comparators.length];
+
+    for (int i = 0; i < comparators.length; i++) {
+      valuesArray[i] = comparators[i].leafValue(docID);
+    }
+
+    return valuesArray;
+  }
+
 }

lucene/core/src/test/org/apache/lucene/search/TestElevationComparator.java

@@ -194,6 +194,11 @@ public void copy(int slot, int doc) throws IOException {
 
         @Override
         public void setScorer(Scorable scorer) {}
+
+        @Override
+        public Integer leafValue(int docID) throws IOException {
+          return docVal(docID);
+        }
       };
     }
 
@@ -212,7 +217,6 @@ public Integer value(int slot) {
        return Integer.valueOf(values[slot]);
      }
 
-
    };
  }
 }

lucene/queries/src/java/org/apache/lucene/queries/function/ValueSource.java

@@ -442,5 +442,10 @@ public int compareTop(int doc) throws IOException {
       final double docValue = docVals.doubleVal(doc);
       return Double.compare(topValue, docValue);
     }
+
+    @Override
+    public Double leafValue(int docID) throws IOException {
+      return docVals.doubleVal(docID);
+    }
   }
 }

lucene/spatial3d/src/java/org/apache/lucene/spatial3d/Geo3DPointDistanceComparator.java

@@ -150,6 +150,11 @@ public int compareTop(int doc) throws IOException {
     return Double.compare(topValue, computeMinimumDistance(doc));
   }
 
+  @Override
+  public Double leafValue(int docID) throws IOException {
+    return computeMinimumDistance(docID);
+  }
+
   double computeMinimumDistance(final int doc) throws IOException {
     if (doc > currentDocs.docID()) {
       currentDocs.advance(doc);

lucene/spatial3d/src/java/org/apache/lucene/spatial3d/Geo3DPointOutsideDistanceComparator.java

@@ -121,6 +121,11 @@ public int compareTop(int doc) throws IOException {
     return Double.compare(topValue, computeMinimumDistance(doc));
   }
 
+  @Override
+  public Double leafValue(int docID) throws IOException {
+    return computeMinimumDistance(docID);
+  }
+
   double computeMinimumDistance(final int doc) throws IOException {
     if (doc > currentDocs.docID()) {
       currentDocs.advance(doc);

solr/core/src/java/org/apache/solr/handler/component/QueryElevationComponent.java

@@ -1220,6 +1220,11 @@ public int compareTop(int doc) {
           final int docValue = docVal(doc);
           return topVal - docValue;  // values will be small enough that there is no overflow concern
         }
+
+        @Override
+        public Integer leafValue(int docID) throws IOException {
+          return docVal(docID);
+        }
       };
     }
   }

solr/core/src/java/org/apache/solr/schema/RandomSortField.java

@@ -154,6 +154,11 @@ public int compareTop(int doc) {
           // values will be positive... no overflow possible.
           return topVal - hash(doc+seed);
         }
+
+        @Override
+        public Integer leafValue(int docID) throws IOException {
+          return hash(docID + seed);
+        }
       };
     }
   };