Require arguments for QueryShardContext creation. (#21196)

The `IndexService#newQueryShardContext()` method creates a QueryShardContext on
shard `0`, with a `null` reader and that uses `System.currentTimeMillis()` to
resolve `now`. This may hide bugs, since the shard id is sometimes used for
query parsing (it is used to salt random score generation in `function_score`),
passing a `null` reader disables query rewriting and for some use-cases, it is
simply not ok to rely on the current timestamp (eg. percolation). So this pull
request removes this method and instead requires that all call sites provide
these parameters explicitly.

2 files changed, 11 insertions, 12 deletions

diff --git a/core/src/main/java/org/elasticsearch/index/IndexService.java b/core/src/main/java/org/elasticsearch/index/IndexService.java
index 0114d68b4e..5fc0d1d27c 100644
--- a/core/src/main/java/org/elasticsearch/index/IndexService.java
+++ b/core/src/main/java/org/elasticsearch/index/IndexService.java
@@ -145,7 +145,10 @@ public class IndexService extends AbstractIndexComponent implements IndicesClust
         this.indexAnalyzers = registry.build(indexSettings);
         this.similarityService = similarityService;
         this.mapperService = new MapperService(indexSettings, indexAnalyzers, similarityService, mapperRegistry,
-            IndexService.this::newQueryShardContext);
+            // we parse all percolator queries as they would be parsed on shard 0
+            () -> newQueryShardContext(0, null, () -> {
+                throw new IllegalArgumentException("Percolator queries are not allowed to use the curent timestamp");
+            }));
         this.indexFieldData = new IndexFieldDataService(indexSettings, indicesFieldDataCache, circuitBreakerService, mapperService);
         this.shardStoreDeleter = shardStoreDeleter;
         this.bigArrays = bigArrays;
@@ -453,7 +456,10 @@ public class IndexService extends AbstractIndexComponent implements IndicesClust
 
     /**
      * Creates a new QueryShardContext. The context has not types set yet, if types are required set them via
-     * {@link QueryShardContext#setTypes(String...)}
+     * {@link QueryShardContext#setTypes(String...)}.
+     *
+     * Passing a {@code null} {@link IndexReader} will return a valid context, however it won't be able to make
+     * {@link IndexReader}-specific optimizations, such as rewriting containing range queries.
      */
     public QueryShardContext newQueryShardContext(int shardId, IndexReader indexReader, LongSupplier nowInMillis) {
         return new QueryShardContext(
@@ -465,15 +471,6 @@ public class IndexService extends AbstractIndexComponent implements IndicesClust
     }
 
     /**
-     * Creates a new QueryShardContext. The context has not types set yet, if types are required set them via
-     * {@link QueryShardContext#setTypes(String...)}. This context may be used for query parsing but cannot be
-     * used for rewriting since it does not know about the current {@link IndexReader}.
-     */
-    public QueryShardContext newQueryShardContext() {
-        return newQueryShardContext(0, null, System::currentTimeMillis);
-    }
-
-    /**
      * The {@link ThreadPool} to use for this index.
      */
     public ThreadPool getThreadPool() {
diff --git a/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java b/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java
index ccca0af652..c8b5cf174f 100644
--- a/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java
+++ b/core/src/main/java/org/elasticsearch/index/query/QueryRewriteContext.java
@@ -86,7 +86,9 @@ public class QueryRewriteContext implements ParseFieldMatcherSupplier {
         return mapperService;
     }
 
-    /** Return the current {@link IndexReader}, or {@code null} if we are on the coordinating node. */
+    /** Return the current {@link IndexReader}, or {@code null} if no index reader is available, for
+     *  instance if we are on the coordinating node or if this rewrite context is used to index
+     *  queries (percolation). */
     public IndexReader getIndexReader() {
         return reader;
     }