MERGE PARTITIONS and DEPENDS ON EXTENSION.

Today, while reviewing another patch, I spotted PostgreSQL behaviour
which I cannot tell if is correct.

-- create relation
reshke=# create table pt (i int) partition by range ( i);
CREATE TABLE

-- create partitions.
reshke=# create table pt1 partition of pt for values from ( 1 ) to (2) ;
CREATE TABLE
reshke=# create table pt2 partition of pt for values from ( 2 ) to (3) ;
CREATE TABLE

-- manually add dependency on extension.
reshke=# alter index pt1_i_idx depends on extension btree_gist ;
ALTER INDEX
reshke=# alter index pt2_i_idx depends on extension btree_gist ;
ALTER INDEX

At this point, `drop extension btree_gist` fails due to existing
dependencies. However, after `alter table pt merge partitions ( pt1 ,
pt2 ) into pt3;` there are no dependencies, and drop extension
executes successfully.

My first impression was that there is no issue as the user created a
new database object, so should manually add dependency on extension.
However I am not 100% in this reasoning.

Any thoughts?

-- 
Best regards,
Kirill Reshke