Fix ALTER EXTENSION SET SCHEMA with objects outside an extension's schema

As coded, the code would use as a base comparison the namespace OID from
the first object scanned in pg_depend when switching its namespace
dependency entry to the new one, and use it as a base of comparison for
any follow-up checks.  It would also be used as the old namespace OID to
switch *from* for the extension's pg_depend entry.  Hence, if the first
object scanned has a namespace different than the one stored in the
extension, we would finish by:
- Not checking that the extension objects map with the extension's
schema.
- Not switching the extension -> namespace dependency entry to the new
namespace provided by the user, making ALTER EXTENSION ineffective.

This issue exists since this command has been introduced in d9572c4 for
relocatable extension, so backpatch all the way down to 11.  The test
case has been provided by Heikki, that I have tweaked a bit to show the
effects on pg_depend for the extension.

Reported-by: Heikki Linnakangas
Author: Michael Paquier, Heikki Linnakangas
Discussion: https://postgr.es/m/20eea594-a05b-4c31-491b-007b6fceef28@iki.fi
Backpatch-through: 11

Author: michaelpq

src/backend/commands/extension.c

@@ -2750,7 +2750,7 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 {
 	Oid			extensionOid;
 	Oid			nspOid;
-	Oid			oldNspOid = InvalidOid;
+	Oid			oldNspOid;
 	AclResult	aclresult;
 	Relation	extRel;
 	ScanKeyData key[2];
@@ -2833,6 +2833,9 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 
 	objsMoved = new_object_addresses();
 
+	/* store the OID of the namespace to-be-changed */
+	oldNspOid = extForm->extnamespace;
+
 	/*
 	 * Scan pg_depend to find objects that depend directly on the extension,
 	 * and alter each one's schema.
@@ -2912,12 +2915,6 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 												 nspOid,
 												 objsMoved);
 
-		/*
-		 * Remember previous namespace of first object that has one
-		 */
-		if (oldNspOid == InvalidOid && dep_oldNspOid != InvalidOid)
-			oldNspOid = dep_oldNspOid;
-
 		/*
 		 * If not all the objects had the same old namespace (ignoring any
 		 * that are not in namespaces), complain.

src/test/modules/test_extensions/expected/test_extensions.out

@@ -312,6 +312,49 @@ Objects in extension "test_ext_cine"
  table ext_cine_tab3
 (9 rows)
 
+--
+-- Test extension with objects outside the extension's schema.
+--
+CREATE SCHEMA test_func_dep1;
+CREATE SCHEMA test_func_dep2;
+CREATE SCHEMA test_func_dep3;
+CREATE EXTENSION test_ext_req_schema1 SCHEMA test_func_dep1;
+ALTER FUNCTION test_func_dep1.dep_req1() SET SCHEMA test_func_dep2;
+SELECT pg_describe_object(classid, objid, objsubid) as obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as objref,
+       deptype
+  FROM pg_depend
+  WHERE classid = 'pg_extension'::regclass AND
+        objid = (SELECT oid FROM pg_extension WHERE extname = 'test_ext_req_schema1')
+  ORDER BY 1, 2;
+              obj               |        objref         | deptype 
+--------------------------------+-----------------------+---------
+ extension test_ext_req_schema1 | schema test_func_dep1 | n
+(1 row)
+
+-- fails, as function dep_req1 is not in the same schema as the extension.
+ALTER EXTENSION test_ext_req_schema1 SET SCHEMA test_func_dep3;
+ERROR:  extension "test_ext_req_schema1" does not support SET SCHEMA
+DETAIL:  function test_func_dep2.dep_req1() is not in the extension's schema "test_func_dep1"
+-- Move back the function, and the extension can be moved.
+ALTER FUNCTION test_func_dep2.dep_req1() SET SCHEMA test_func_dep1;
+ALTER EXTENSION test_ext_req_schema1 SET SCHEMA test_func_dep3;
+SELECT pg_describe_object(classid, objid, objsubid) as obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as objref,
+       deptype
+  FROM pg_depend
+  WHERE classid = 'pg_extension'::regclass AND
+        objid = (SELECT oid FROM pg_extension WHERE extname = 'test_ext_req_schema1')
+  ORDER BY 1, 2;
+              obj               |        objref         | deptype 
+--------------------------------+-----------------------+---------
+ extension test_ext_req_schema1 | schema test_func_dep3 | n
+(1 row)
+
+DROP EXTENSION test_ext_req_schema1 CASCADE;
+DROP SCHEMA test_func_dep1;
+DROP SCHEMA test_func_dep2;
+DROP SCHEMA test_func_dep3;
 --
 -- Test @extschema:extname@ syntax and no_relocate option
 --

src/test/modules/test_extensions/sql/test_extensions.sql

@@ -210,6 +210,38 @@ ALTER EXTENSION test_ext_cine UPDATE TO '1.1';
 
 \dx+ test_ext_cine
 
+--
+-- Test extension with objects outside the extension's schema.
+--
+CREATE SCHEMA test_func_dep1;
+CREATE SCHEMA test_func_dep2;
+CREATE SCHEMA test_func_dep3;
+CREATE EXTENSION test_ext_req_schema1 SCHEMA test_func_dep1;
+ALTER FUNCTION test_func_dep1.dep_req1() SET SCHEMA test_func_dep2;
+SELECT pg_describe_object(classid, objid, objsubid) as obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as objref,
+       deptype
+  FROM pg_depend
+  WHERE classid = 'pg_extension'::regclass AND
+        objid = (SELECT oid FROM pg_extension WHERE extname = 'test_ext_req_schema1')
+  ORDER BY 1, 2;
+-- fails, as function dep_req1 is not in the same schema as the extension.
+ALTER EXTENSION test_ext_req_schema1 SET SCHEMA test_func_dep3;
+-- Move back the function, and the extension can be moved.
+ALTER FUNCTION test_func_dep2.dep_req1() SET SCHEMA test_func_dep1;
+ALTER EXTENSION test_ext_req_schema1 SET SCHEMA test_func_dep3;
+SELECT pg_describe_object(classid, objid, objsubid) as obj,
+       pg_describe_object(refclassid, refobjid, refobjsubid) as objref,
+       deptype
+  FROM pg_depend
+  WHERE classid = 'pg_extension'::regclass AND
+        objid = (SELECT oid FROM pg_extension WHERE extname = 'test_ext_req_schema1')
+  ORDER BY 1, 2;
+DROP EXTENSION test_ext_req_schema1 CASCADE;
+DROP SCHEMA test_func_dep1;
+DROP SCHEMA test_func_dep2;
+DROP SCHEMA test_func_dep3;
+
 --
 -- Test @extschema:extname@ syntax and no_relocate option
 --