Fix failures in validateForeignKeyConstraint's slow path.

The foreign-key-checking loop in ATRewriteTables failed to ignore
relations without storage (e.g., partitioned tables), unlike the
initial loop.  This accidentally worked as long as RI_Initial_Check
succeeded, which it does in most practical cases (including all the
ones exercised in the existing regression tests :-().  However, if
that failed, as for instance when there are permissions issues,
then we entered the slow fire-the-trigger-on-each-tuple path.
And that would try to read from the referencing relation, and fail
if it lacks storage.

A second problem, recently introduced in HEAD, was that this loop
had been broken by sloppy refactoring for the tableam API changes.

Repair both issues, and add a regression test case so we have some
coverage on this code path.  Back-patch as needed to v11.

(It looks like this code could do with additional bulletproofing,
but let's get a working test case in place first.)

Hadi Moshayedi, Tom Lane, Andres Freund

Discussion: https://postgr.es/m/CAK=1=WrnNmBbe5D9sm3t0a6dnAq3cdbF1vXY816j1wsMqzC8bw@mail.gmail.com
Discussion: https://postgr.es/m/19030.1554574075@sss.pgh.pa.us
Discussion: https://postgr.es/m/20190325180405.jytoehuzkeozggxx%40alap3.anarazel.de

src/backend/commands/tablecmds.c

@@ -4534,6 +4534,15 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode)
 		Relation	rel = NULL;
 		ListCell   *lcon;
 
+		/*
+		 * Foreign tables have no storage, nor do partitioned tables and
+		 * indexes.
+		 */
+		if (tab->relkind == RELKIND_FOREIGN_TABLE ||
+			tab->relkind == RELKIND_PARTITIONED_TABLE ||
+			tab->relkind == RELKIND_PARTITIONED_INDEX)
+			continue;
+
 		foreach(lcon, tab->constraints)
 		{
 			NewConstraint *con = lfirst(lcon);

src/test/regress/expected/foreign_key.out

@@ -1775,12 +1775,38 @@ CREATE TABLE fk_partitioned_fk_2_2 PARTITION OF fk_partitioned_fk_2 FOR VALUES F
 INSERT INTO fk_partitioned_fk_2 VALUES (1600, 601), (1600, 1601);
 ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_2
   FOR VALUES IN (1600);
-ERROR:  insert or update on table "fk_partitioned_fk_2" violates foreign key constraint "fk_partitioned_fk_a_fkey"
+ERROR:  insert or update on table "fk_partitioned_fk_2_1" violates foreign key constraint "fk_partitioned_fk_a_fkey"
 DETAIL:  Key (a, b)=(1600, 601) is not present in table "fk_notpartitioned_pk".
 INSERT INTO fk_notpartitioned_pk VALUES (1600, 601), (1600, 1601);
 ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_2
   FOR VALUES IN (1600);
 -- leave these tables around intentionally
+-- test the case when the referenced table is owned by a different user
+create role regress_other_partitioned_fk_owner;
+grant references on fk_notpartitioned_pk to regress_other_partitioned_fk_owner;
+set role regress_other_partitioned_fk_owner;
+create table other_partitioned_fk(a int, b int) partition by list (a);
+create table other_partitioned_fk_1 partition of other_partitioned_fk
+  for values in (2048);
+insert into other_partitioned_fk
+  select 2048, x from generate_series(1,10) x;
+-- this should fail
+alter table other_partitioned_fk add foreign key (a, b)
+  references fk_notpartitioned_pk(a, b);
+ERROR:  insert or update on table "other_partitioned_fk_1" violates foreign key constraint "other_partitioned_fk_a_fkey"
+DETAIL:  Key (a, b)=(2048, 1) is not present in table "fk_notpartitioned_pk".
+-- add the missing keys and retry
+reset role;
+insert into fk_notpartitioned_pk (a, b)
+  select 2048, x from generate_series(1,10) x;
+set role regress_other_partitioned_fk_owner;
+alter table other_partitioned_fk add foreign key (a, b)
+  references fk_notpartitioned_pk(a, b);
+-- clean up
+drop table other_partitioned_fk;
+reset role;
+revoke all on fk_notpartitioned_pk from regress_other_partitioned_fk_owner;
+drop role regress_other_partitioned_fk_owner;
 -- Test creating a constraint at the parent that already exists in partitions.
 -- There should be no duplicated constraints, and attempts to drop the
 -- constraint in partitions should raise appropriate errors.

src/test/regress/sql/foreign_key.sql

@@ -1290,6 +1290,31 @@ ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_2
 
 -- leave these tables around intentionally
 
+-- test the case when the referenced table is owned by a different user
+create role regress_other_partitioned_fk_owner;
+grant references on fk_notpartitioned_pk to regress_other_partitioned_fk_owner;
+set role regress_other_partitioned_fk_owner;
+create table other_partitioned_fk(a int, b int) partition by list (a);
+create table other_partitioned_fk_1 partition of other_partitioned_fk
+  for values in (2048);
+insert into other_partitioned_fk
+  select 2048, x from generate_series(1,10) x;
+-- this should fail
+alter table other_partitioned_fk add foreign key (a, b)
+  references fk_notpartitioned_pk(a, b);
+-- add the missing keys and retry
+reset role;
+insert into fk_notpartitioned_pk (a, b)
+  select 2048, x from generate_series(1,10) x;
+set role regress_other_partitioned_fk_owner;
+alter table other_partitioned_fk add foreign key (a, b)
+  references fk_notpartitioned_pk(a, b);
+-- clean up
+drop table other_partitioned_fk;
+reset role;
+revoke all on fk_notpartitioned_pk from regress_other_partitioned_fk_owner;
+drop role regress_other_partitioned_fk_owner;
+
 -- Test creating a constraint at the parent that already exists in partitions.
 -- There should be no duplicated constraints, and attempts to drop the
 -- constraint in partitions should raise appropriate errors.