Address Jim's comments

docs/reference/migration/migrate_7_0/search.asciidoc

@@ -148,4 +148,12 @@ instead which is a more appropriate value for a scenario where scores are not av
 ==== Negative boosts are not allowed
 
 Setting a negative `boost` in a query, deprecated in 6x, are not allowed in this version.
-To deboost a specific query you can use a `boost` comprise between 0 and 1.
+To deboost a specific query you can use a `boost` comprise between 0 and 1.
+
+[float]
+==== Negative scores are not allowed in Function Score Query
+
+Negative scores in the Function Score Query are deprecated in 6.x, and are
+not allowed in this version. If a negative score is produced as a result
+of computation (e.g. in `script_score` or `field_value_factor` functions),
+an error will be thrown.

modules/lang-painless/src/test/resources/rest-api-spec/test/painless/30_search.yml

@@ -448,35 +448,35 @@
 
 "Exception on negative score":
     - skip:
-          version: " - 6.99.99"
-          reason: "check on negative scores was added from 7.0.0 on"
-
-    - do:
-          index:
-              index: test
-              type: test
-              id: 1
-              body: { "test": "value beck", "num1": 1.0 }
-    - do:
-          indices.refresh: {}
-
-    - do:
-          catch: bad_request
-          search:
-              index: test
-              body:
-                  query:
-                      function_score:
-                          query:
-                              term:
-                                  test: value
-                          "functions": [{
-                                            "script_score": {
-                                                "script": {
-                                                    "lang": "painless",
-                                                    "source": "doc['num1'].value - 10.0"
-                                                }
-                                            }
-                                        }]
+        version: " - 6.99.99"
+        reason: "check on negative scores was added from 7.0.0 on"
+
+    - do:
+        index:
+            index: test
+            type: test
+            id: 1
+            body: { "test": "value beck", "num1": 1.0 }
+    - do:
+        indices.refresh: {}
+
+    - do:
+        catch: bad_request
+        search:
+            index: test
+            body:
+                query:
+                    function_score:
+                        query:
+                            term:
+                                test: value
+                        "functions": [{
+                            "script_score": {
+                                "script": {
+                                    "lang": "painless",
+                                    "source": "doc['num1'].value - 10.0"
+                                }
+                            }
+                        }]
     - match: { error.root_cause.0.type: "illegal_argument_exception" }
     - match: { error.root_cause.0.reason: "script score function must not produce negative scores, but got: [-9.0]"}

server/src/main/java/org/elasticsearch/common/lucene/search/function/FunctionScoreQuery.java

@@ -382,7 +382,7 @@ public float score() throws IOException {
             }
             double factor = computeScore(docId, subQueryScore);
             float finalScore = scoreCombiner.combine(subQueryScore, factor, maxBoost);
-            if (finalScore == Float.NEGATIVE_INFINITY || Float.isNaN(finalScore)) {
+            if (finalScore < 0 || Float.isNaN(finalScore)) {
                 /*
                   These scores are invalid for score based {@link org.apache.lucene.search.TopDocsCollector}s.
                   See {@link org.apache.lucene.search.TopScoreDocCollector} for details.