[BACKPORT 2.6][#6470] YSQL: Enable ALTER SCHEMA RENAME

Summary:
DocDB layer knows nothing about postgres schemas. This information in stored only in postgres sys catalog.
It is enough to allow the `ALTER SCHEMA RENAME` command on parser level to support schema reaming.

Original commit: D12387 / 39b2b6b

Test Plan:
Jenkins: rebase: 2.6
postgres's regress test `namespace.sql` was integrated as `yb_pg_namespace.sql`

```
./yb_build.sh --java-test 'org.yb.pgsql.TestPgRegressPgMiscIndependent'
```

Reviewers: alex, mihnea

Reviewed By: mihnea

Subscribers: yql

Differential Revision: https://phabricator.dev.yugabyte.com/D12471

src/postgres/src/backend/parser/gram.y

@@ -1392,6 +1392,8 @@ CreateSchemaStmt:
 					/* One can omit the schema name or the authorization id. */
 					n->schemaname = $3;
 					n->authrole = $5;
+					if ($6 != NIL)
+						parser_ybc_not_support(@6, "CREATE SCHEMA with elements");
 					n->schemaElts = $6;
 					n->if_not_exists = false;
 					$$ = (Node *)n;
@@ -1402,6 +1404,8 @@ CreateSchemaStmt:
 					/* ...but not both */
 					n->schemaname = $3;
 					n->authrole = NULL;
+					if ($4 != NIL)
+						parser_ybc_not_support(@4, "CREATE SCHEMA with elements");
 					n->schemaElts = $4;
 					n->if_not_exists = false;
 					$$ = (Node *)n;
@@ -1446,7 +1450,6 @@ OptSchemaName:
 OptSchemaEltList:
 			OptSchemaEltList schema_stmt
 				{
-					parser_ybc_not_support(@2, "CREATE SCHEMA with elements");
 					if (@$ < 0)			/* see comments for YYLLOC_DEFAULT */
 						@$ = @2;
 					$$ = lappend($1, $2);
@@ -9413,7 +9416,6 @@ RenameStmt: ALTER AGGREGATE aggregate_with_argtypes RENAME TO name
 				}
 			| ALTER SCHEMA name RENAME TO name
 				{
-					parser_ybc_not_support(@1, "ALTER SCHEMA");
 					RenameStmt *n = makeNode(RenameStmt);
 					n->renameType = OBJECT_SCHEMA;
 					n->subname = $3;

src/postgres/src/test/regress/expected/yb_pg_namespace.out

@@ -0,0 +1,80 @@
+--
+-- Regression tests for schemas (namespaces)
+--
+CREATE SCHEMA test_ns_schema_1
+       CREATE UNIQUE INDEX abc_a_idx ON abc (a)
+       CREATE VIEW abc_view AS
+              SELECT a+1 AS a, b+1 AS b FROM abc
+       CREATE TABLE abc (
+              a serial,
+              b int UNIQUE
+       );
+ERROR:  CREATE SCHEMA with elements not supported yet
+LINE 2:        CREATE UNIQUE INDEX abc_a_idx ON abc (a)
+               ^
+HINT:  Please report the issue on https://github.com/YugaByte/yugabyte-db/issues
+-- TODO(dmitry): Remove separate statements for creation each element in schema after
+--               `schema creation with elements` command will be supported.
+CREATE SCHEMA test_ns_schema_1;
+CREATE TABLE test_ns_schema_1.abc (a serial, b int UNIQUE);
+CREATE UNIQUE INDEX abc_a_idx ON test_ns_schema_1.abc (a);
+CREATE VIEW test_ns_schema_1.abc_view AS SELECT a+1 AS a, b+1 AS b FROM test_ns_schema_1.abc;
+-- verify that the objects were created
+SELECT COUNT(*) FROM pg_class WHERE relnamespace =
+    (SELECT oid FROM pg_namespace WHERE nspname = 'test_ns_schema_1');
+ count
+-------
+     5
+(1 row)
+
+INSERT INTO test_ns_schema_1.abc DEFAULT VALUES;
+INSERT INTO test_ns_schema_1.abc DEFAULT VALUES;
+INSERT INTO test_ns_schema_1.abc DEFAULT VALUES;
+SELECT * FROM test_ns_schema_1.abc ORDER BY a;
+ a | b
+---+---
+ 1 |
+ 2 |
+ 3 |
+(3 rows)
+
+SELECT * FROM test_ns_schema_1.abc_view ORDER BY a;
+ a | b
+---+---
+ 2 |
+ 3 |
+ 4 |
+(3 rows)
+
+ALTER SCHEMA test_ns_schema_1 RENAME TO test_ns_schema_renamed;
+SELECT COUNT(*) FROM pg_class WHERE relnamespace =
+    (SELECT oid FROM pg_namespace WHERE nspname = 'test_ns_schema_1');
+ count
+-------
+     0
+(1 row)
+
+-- test IF NOT EXISTS cases
+CREATE SCHEMA test_ns_schema_renamed; -- fail, already exists
+ERROR:  schema "test_ns_schema_renamed" already exists
+CREATE SCHEMA IF NOT EXISTS test_ns_schema_renamed; -- ok with notice
+NOTICE:  schema "test_ns_schema_renamed" already exists, skipping
+CREATE SCHEMA IF NOT EXISTS test_ns_schema_renamed -- fail, disallowed
+       CREATE TABLE abc (
+              a serial,
+              b int UNIQUE
+       );
+ERROR:  CREATE SCHEMA IF NOT EXISTS cannot include schema elements
+LINE 2:        CREATE TABLE abc (
+               ^
+DROP SCHEMA test_ns_schema_renamed CASCADE;
+NOTICE:  drop cascades to 2 other objects
+DETAIL:  drop cascades to table test_ns_schema_renamed.abc
+drop cascades to view test_ns_schema_renamed.abc_view
+-- verify that the objects were dropped
+SELECT COUNT(*) FROM pg_class WHERE relnamespace =
+    (SELECT oid FROM pg_namespace WHERE nspname = 'test_ns_schema_renamed');
+ count
+-------
+     0
+(1 row)

src/postgres/src/test/regress/sql/yb_pg_namespace.sql

@@ -0,0 +1,51 @@
+--
+-- Regression tests for schemas (namespaces)
+--
+
+CREATE SCHEMA test_ns_schema_1
+       CREATE UNIQUE INDEX abc_a_idx ON abc (a)
+
+       CREATE VIEW abc_view AS
+              SELECT a+1 AS a, b+1 AS b FROM abc
+
+       CREATE TABLE abc (
+              a serial,
+              b int UNIQUE
+       );
+
+-- TODO(dmitry): Remove separate statements for creation each element in schema after
+--               `schema creation with elements` command will be supported.
+CREATE SCHEMA test_ns_schema_1;
+CREATE TABLE test_ns_schema_1.abc (a serial, b int UNIQUE);
+CREATE UNIQUE INDEX abc_a_idx ON test_ns_schema_1.abc (a);
+CREATE VIEW test_ns_schema_1.abc_view AS SELECT a+1 AS a, b+1 AS b FROM test_ns_schema_1.abc;
+
+-- verify that the objects were created
+SELECT COUNT(*) FROM pg_class WHERE relnamespace =
+    (SELECT oid FROM pg_namespace WHERE nspname = 'test_ns_schema_1');
+
+INSERT INTO test_ns_schema_1.abc DEFAULT VALUES;
+INSERT INTO test_ns_schema_1.abc DEFAULT VALUES;
+INSERT INTO test_ns_schema_1.abc DEFAULT VALUES;
+
+SELECT * FROM test_ns_schema_1.abc ORDER BY a;
+SELECT * FROM test_ns_schema_1.abc_view ORDER BY a;
+
+ALTER SCHEMA test_ns_schema_1 RENAME TO test_ns_schema_renamed;
+SELECT COUNT(*) FROM pg_class WHERE relnamespace =
+    (SELECT oid FROM pg_namespace WHERE nspname = 'test_ns_schema_1');
+
+-- test IF NOT EXISTS cases
+CREATE SCHEMA test_ns_schema_renamed; -- fail, already exists
+CREATE SCHEMA IF NOT EXISTS test_ns_schema_renamed; -- ok with notice
+CREATE SCHEMA IF NOT EXISTS test_ns_schema_renamed -- fail, disallowed
+       CREATE TABLE abc (
+              a serial,
+              b int UNIQUE
+       );
+
+DROP SCHEMA test_ns_schema_renamed CASCADE;
+
+-- verify that the objects were dropped
+SELECT COUNT(*) FROM pg_class WHERE relnamespace =
+    (SELECT oid FROM pg_namespace WHERE nspname = 'test_ns_schema_renamed');

src/postgres/src/test/regress/yb_pg_misc_independent_serial_schedule

@@ -17,6 +17,7 @@ test: yb_pg_drop_operator
 test: yb_prepare
 test: yb_sequence
 test: yb_pg_identity
+test: yb_pg_namespace
 
 # Features that are explicitly disabled and therefore should not work
 test: yb_disabled