position_in_partition: Introduce after_key()

position_in_partition.hh

@@ -207,6 +207,10 @@ public:
     position_in_partition(after_clustering_row_tag_t, clustering_key_prefix ck)
         // FIXME: Use lexicographical_relation::before_strictly_prefixed here. Refs #1446
         : _type(partition_region::clustered), _bound_weight(1), _ck(std::move(ck)) { }
+    position_in_partition(after_clustering_row_tag_t, position_in_partition_view pos)
+        : _type(partition_region::clustered)
+        , _bound_weight(pos._bound_weight ? pos._bound_weight : 1)
+        , _ck(*pos._ck) { }
     position_in_partition(before_clustering_row_tag_t, clustering_key_prefix ck)
         : _type(partition_region::clustered), _bound_weight(-1), _ck(std::move(ck)) { }
     position_in_partition(range_tag_t, bound_view bv)
@@ -237,6 +241,13 @@ public:
         return {after_clustering_row_tag_t(), std::move(ck)};
     }
 
+    // If given position is a clustering row position, returns a position
+    // right after it. Otherwise returns it unchanged.
+    // The position "pos" must be a clustering position.
+    static position_in_partition after_key(position_in_partition_view pos) {
+        return {after_clustering_row_tag_t(), pos};
+    }
+
     static position_in_partition for_key(clustering_key ck) {
         return {clustering_row_tag_t(), std::move(ck)};
     }