Tests: foreign key non colocated tests (#4841)

Earlier versions of Citus (pre 9.0) had a bug where a user was able to get in a situation where a foreign key between two non-colocated tables was allowed. This was caused by the wrongful scoping together with only setting to on of a boolean variable in a loop, causing the `true` from an earlier iteration to leak into a new iteration.

This was 'by accident' solved in a refactor that was executed in the preparation of the 9.0 release. Only recently we had a user running into this and it was tracked down to this behaviour.

Given the dire situation a user could get them self into when running into this bug we have backported a fix to the latest 8.3 release branch.

To make sure this regression does not happen anymore in the future I propose we add the tests from the backport to our mainline.

For reference: https://github.com/citusdata/citus/pull/4840

src/test/regress/expected/foreign_key_to_reference_table.out

@@ -1609,6 +1609,39 @@ BEGIN;
 ROLLBACK;
 DROP TABLE referenced_table CASCADE;
 DROP TABLE referencing_table;
+-- tests specific to an edgecase in citus 8.x where it was possible to create foreign keys
+-- in between colocation groups due to a bug of foreign key to reference tables
+CREATE TABLE t1 (a int PRIMARY KEY, b text);
+CREATE TABLE t2 (a bigint PRIMARY KEY, b text);
+CREATE TABLE r1 (a int PRIMARY KEY, b text);
+SELECT create_distributed_table('t1', 'a');
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+SELECT create_distributed_table('t2', 'a');
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+SELECT create_reference_table('r1');
+ create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- this always fails as it should be
+ALTER TABLE t1 ADD CONSTRAINT c1 FOREIGN KEY (a) REFERENCES t2(a);
+ERROR:  cannot create foreign key constraint since relations are not colocated or not referencing a reference table
+DETAIL:  A distributed table can only have foreign keys if it is referencing another colocated hash distributed table or a reference table
+-- after we create a foreign key to the reference table, that has a lower order by name,
+-- we would have been able to create a FK to non-colocated tables
+ALTER TABLE t1 ADD CONSTRAINT c2 FOREIGN KEY (a) REFERENCES r1(a);
+ALTER TABLE t1 ADD CONSTRAINT c3 FOREIGN KEY (a) REFERENCES t2(a);
+ERROR:  cannot create foreign key constraint since relations are not colocated or not referencing a reference table
+DETAIL:  A distributed table can only have foreign keys if it is referencing another colocated hash distributed table or a reference table
 DROP SCHEMA fkey_reference_table CASCADE;
 SET search_path TO DEFAULT;
 RESET client_min_messages;

src/test/regress/sql/foreign_key_to_reference_table.sql

@@ -918,6 +918,25 @@ ROLLBACK;
 DROP TABLE referenced_table CASCADE;
 DROP TABLE referencing_table;
 
+-- tests specific to an edgecase in citus 8.x where it was possible to create foreign keys
+-- in between colocation groups due to a bug of foreign key to reference tables
+CREATE TABLE t1 (a int PRIMARY KEY, b text);
+CREATE TABLE t2 (a bigint PRIMARY KEY, b text);
+CREATE TABLE r1 (a int PRIMARY KEY, b text);
+
+SELECT create_distributed_table('t1', 'a');
+SELECT create_distributed_table('t2', 'a');
+SELECT create_reference_table('r1');
+
+-- this always fails as it should be
+ALTER TABLE t1 ADD CONSTRAINT c1 FOREIGN KEY (a) REFERENCES t2(a);
+
+-- after we create a foreign key to the reference table, that has a lower order by name,
+-- we would have been able to create a FK to non-colocated tables
+ALTER TABLE t1 ADD CONSTRAINT c2 FOREIGN KEY (a) REFERENCES r1(a);
+ALTER TABLE t1 ADD CONSTRAINT c3 FOREIGN KEY (a) REFERENCES t2(a);
+
+
 DROP SCHEMA fkey_reference_table CASCADE;
 SET search_path TO DEFAULT;
 RESET client_min_messages;