Make can-match support already skipped shard iterators

Author: benchaplin

server/src/main/java/org/elasticsearch/action/search/CanMatchPreFilterSearchPhase.java

@@ -186,6 +186,12 @@ private void runCoordinatorRewritePhase() {
         assert assertSearchCoordinationThread();
         final List<SearchShardIterator> matchedShardLevelRequests = new ArrayList<>();
         for (SearchShardIterator searchShardIterator : shardsIts) {
+            if (searchShardIterator.prefiltered() == false && searchShardIterator.skip()) {
+                // This implies the iterator was skipped due to an index level block,
+                // not a remote can-match run.
+                continue;
+            }
+
             final CanMatchNodeRequest canMatchNodeRequest = new CanMatchNodeRequest(
                 request,
                 searchShardIterator.getOriginalIndices().indicesOptions(),

server/src/main/java/org/elasticsearch/action/search/SearchShardIterator.java

@@ -60,7 +60,8 @@ public SearchShardIterator(@Nullable String clusterAlias, ShardId shardId, List<
      * @param shardId         shard id of the group
      * @param shards          shards to iterate
      * @param originalIndices the indices that the search request originally related to (before any rewriting happened)
-     * @param skip            if true, then this group won't have matches, and it can be safely skipped from the search
+     * @param skip            if true, then this group won't have matches (due to an index level block),
+     *                        and it can be safely skipped from the search
      */
     public SearchShardIterator(
         @Nullable String clusterAlias,
@@ -83,7 +84,8 @@ public SearchShardIterator(
      * @param searchContextId        the point-in-time specified for this group if exists
      * @param searchContextKeepAlive the time interval that data nodes should extend the keep alive of the point-in-time
      * @param prefiltered            if true, then this group already executed the can_match phase
-     * @param skip                   if true, then this group won't have matches, and it can be safely skipped from the search
+     * @param skip                   if true, then this group won't have matches (due to can match, or an index level block),
+     *                               and it can be safely skipped from the search
      */
     public SearchShardIterator(
         @Nullable String clusterAlias,