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.

1 files changed, 3 insertions, 1 deletions

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;
     }