From c92ec1c5d7c516b83e6264528e88ce42e8f6913e Mon Sep 17 00:00:00 2001
From: lipsill <39668292+lipsill@users.noreply.github.com>
Date: Wed, 12 Sep 2018 09:16:40 +0200
Subject: [PATCH] Forbid negative `weight` in Function Score Query (#33390)

This change forbids negative `weight` in Function Score query. Negative scores are forbidden in Lucene 8.
---
 .../query/functionscore/ScoreFunctionBuilder.java    | 12 +++++++++---
 .../FunctionScoreQueryBuilderTests.java              |  3 +++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/index/query/functionscore/ScoreFunctionBuilder.java b/server/src/main/java/org/elasticsearch/index/query/functionscore/ScoreFunctionBuilder.java
index c64f1b1e403..6cfe7d177da 100644
--- a/server/src/main/java/org/elasticsearch/index/query/functionscore/ScoreFunctionBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/functionscore/ScoreFunctionBuilder.java
@@ -24,7 +24,6 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.lucene.search.function.ScoreFunction;
 import org.elasticsearch.common.lucene.search.function.WeightFactorFunction;
-import org.elasticsearch.common.xcontent.ToXContent.Params;
 import org.elasticsearch.common.xcontent.ToXContentFragment;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.index.query.QueryShardContext;
@@ -46,7 +45,7 @@ public abstract class ScoreFunctionBuilder<FB extends ScoreFunctionBuilder<FB>>
      * Read from a stream.
      */
     public ScoreFunctionBuilder(StreamInput in) throws IOException {
-        weight = in.readOptionalFloat();
+        weight = checkWeight(in.readOptionalFloat());
     }
 
     @Override
@@ -70,10 +69,17 @@ public abstract class ScoreFunctionBuilder<FB extends ScoreFunctionBuilder<FB>>
      */
     @SuppressWarnings("unchecked")
     public final FB setWeight(float weight) {
-        this.weight = weight;
+        this.weight = checkWeight(weight);
         return (FB) this;
     }
 
+    private Float checkWeight(Float weight) {
+        if (weight != null && Float.compare(weight, 0) < 0) {
+            throw new IllegalArgumentException("[weight] cannot be negative for a filtering function");
+        }
+        return weight;
+    }
+
     /**
      * The weight applied to the function before combining.
      */
diff --git a/server/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java b/server/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java
index cc224019100..624205a1a3c 100644
--- a/server/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java
+++ b/server/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java
@@ -20,6 +20,7 @@
 package org.elasticsearch.index.query.functionscore;
 
 import com.fasterxml.jackson.core.JsonParseException;
+
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.Query;
@@ -272,6 +273,8 @@ public class FunctionScoreQueryBuilderTests extends AbstractQueryTestCase<Functi
         FunctionScoreQueryBuilder builder = new FunctionScoreQueryBuilder(matchAllQuery());
         expectThrows(IllegalArgumentException.class, () -> builder.scoreMode(null));
         expectThrows(IllegalArgumentException.class, () -> builder.boostMode(null));
+        expectThrows(IllegalArgumentException.class,
+                () -> new FunctionScoreQueryBuilder.FilterFunctionBuilder(new WeightBuilder().setWeight(-1 * randomFloat())));
     }
 
     public void testParseFunctionsArray() throws IOException {