Changelog: Test that we error out for DROP EXPRESSION

PG13 now supports dropping expression from a column such as generated
columns. We error out with this currently.

Changelog entry in postgres:
Add ALTER TABLE clause DROP EXPRESSION to remove generated properties from columns (Peter Eisentraut)

src/test/regress/expected/pg13.out

@@ -31,6 +31,39 @@ ERROR:  parallel vacuum degree must be between 0 and 1024
 VACUUM (PARALLEL) dist_table;
 ERROR:  parallel option requires a value between 0 and 1024
 RESET client_min_messages;
+-- test alter table alter column drop expression
+CREATE TABLE generated_col_table(a int, b int GENERATED ALWAYS AS (a * 10) STORED);
+SELECT create_distributed_table('generated_col_table', 'a');
+NOTICE:  issuing BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED;SELECT assign_distributed_transaction_id(xx, xx, 'xxxxxxx');
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED;SELECT assign_distributed_transaction_id(xx, xx, 'xxxxxxx');
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing SELECT worker_apply_shard_ddl_command (65002, 'test_pg13', 'CREATE TABLE test_pg13.generated_col_table (a integer, b integer GENERATED ALWAYS AS ((a * 10)) STORED)');SELECT worker_apply_shard_ddl_command (65002, 'test_pg13', 'ALTER TABLE test_pg13.generated_col_table OWNER TO postgres')
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing SELECT worker_apply_shard_ddl_command (65003, 'test_pg13', 'CREATE TABLE test_pg13.generated_col_table (a integer, b integer GENERATED ALWAYS AS ((a * 10)) STORED)');SELECT worker_apply_shard_ddl_command (65003, 'test_pg13', 'ALTER TABLE test_pg13.generated_col_table OWNER TO postgres')
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing PREPARE TRANSACTION 'citus_0_13977_182_2'
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing PREPARE TRANSACTION 'citus_0_13977_182_3'
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing COMMIT PREPARED 'citus_0_13977_182_2'
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing COMMIT PREPARED 'citus_0_13977_182_3'
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+INSERT INTO generated_col_table VALUES (1);
+NOTICE:  issuing INSERT INTO test_pg13.generated_col_table_65002 (a) VALUES (1)
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+-- Make sure that we currently error out
+ALTER TABLE generated_col_table ALTER COLUMN b DROP EXPRESSION;
+ERROR:  alter table command is currently unsupported
+DETAIL:  Only ADD|DROP COLUMN, SET|DROP NOT NULL, SET|DROP DEFAULT, ADD|DROP|VALIDATE CONSTRAINT, SET (), RESET (), ATTACH|DETACH PARTITION and TYPE subcommands are supported.
 RESET citus.log_remote_commands;
 drop schema test_pg13 cascade;
-NOTICE:  drop cascades to table dist_table
+NOTICE:  drop cascades to 2 other objects
+DETAIL:  drop cascades to table dist_table
+drop cascades to table generated_col_table

src/test/regress/sql/pg13.sql

@@ -22,6 +22,14 @@ VACUUM (PARALLEL -5) dist_table;
 VACUUM (PARALLEL) dist_table;
 
 RESET client_min_messages;
+
+-- test alter table alter column drop expression
+CREATE TABLE generated_col_table(a int, b int GENERATED ALWAYS AS (a * 10) STORED);
+SELECT create_distributed_table('generated_col_table', 'a');
+INSERT INTO generated_col_table VALUES (1);
+-- Make sure that we currently error out
+ALTER TABLE generated_col_table ALTER COLUMN b DROP EXPRESSION;
+
 RESET citus.log_remote_commands;
 
 drop schema test_pg13 cascade;