BUG #15247: At 'ALTER TABLE ADD COLUMN fast default' , Set attmissingval to NULL in the pg_attribute, query fail

The following bug has been logged on the website:

Bug reference: 15247
Logged by: guangxian li
Email address: liguangxian1995(at)gmail(dot)com
PostgreSQL version: 11beta1
Operating system: debian 6.4.0
Description:

Dear developer:
Steps:
(1) create table test(a int);
(2) insert into test values(1),(2),(3);
(3) alter table test add b int not null default 0;
(4) update pg_attribute set attmissingval = NULL where attname = 'b';
(5) select b from test;
Then,query the b field from the test table(select b from test;) , lead to
server closed the connection unexpectedly .

I think this a bug ,or not. Meanwhile,I think we should add an statement
--if(att->atthasmissing && tupleDesc->constr->missing) .Not Assert().

So, Hope to get your reply,Thanks again.

Next is a patch.

--- a/src/backend/access/common/heaptuple.c
+++ b/src/backend/access/common/heaptuple.c
@@ -91,7 +91,7 @@ getmissingattr(TupleDesc tupleDesc,

att = TupleDescAttr(tupleDesc, attnum - 1);

- if (att->atthasmissing)
+ if (att->atthasmissing && tupleDesc->constr->missing)
{
AttrMissing *attrmiss;