Recalculate search_path after ALTER ROLE.

Renaming a role can affect the meaning of the special string $user, so
must cause search_path to be recalculated.

Discussion: https://postgr.es/m/186761d32c0255debbdf50b6310b581b9c973e6c.camel@j-davis.com
Reviewed-by: Nathan Bossart, Michael Paquier
Backpatch-through: 11

src/backend/catalog/namespace.c

@@ -4399,11 +4399,15 @@ InitializeSearchPath(void)
 	{
 		/*
 		 * In normal mode, arrange for a callback on any syscache invalidation
-		 * of pg_namespace rows.
+		 * of pg_namespace or pg_authid rows. (Changing a role name may affect
+		 * the meaning of the special string $user.)
 		 */
 		CacheRegisterSyscacheCallback(NAMESPACEOID,
 									  NamespaceCallback,
 									  (Datum) 0);
+		CacheRegisterSyscacheCallback(AUTHOID,
+									  NamespaceCallback,
+									  (Datum) 0);
 		/* Force search path to be recomputed on next use */
 		baseSearchPathValid = false;
 	}

src/test/isolation/expected/search-path-inval.out

@@ -0,0 +1,97 @@
+Parsed test spec with 3 sessions
+
+starting permutation: s1a s2a s1a s2b
+step s1a: 
+    SELECT CURRENT_USER;
+    SHOW search_path;
+    SELECT t FROM x;
+
+current_user    
+----------------
+regress_sp_user1
+(1 row)
+
+search_path               
+--------------------------
+"$user", regress_sp_public
+(1 row)
+
+t                         
+--------------------------
+data in regress_sp_user1.x
+(1 row)
+
+step s2a: 
+    ALTER ROLE regress_sp_user1 RENAME TO regress_sp_user2;
+
+step s1a: 
+    SELECT CURRENT_USER;
+    SHOW search_path;
+    SELECT t FROM x;
+
+current_user    
+----------------
+regress_sp_user2
+(1 row)
+
+search_path               
+--------------------------
+"$user", regress_sp_public
+(1 row)
+
+t                          
+---------------------------
+data in regress_sp_public.x
+(1 row)
+
+step s2b: 
+    ALTER ROLE regress_sp_user2 RENAME TO regress_sp_user1;
+
+
+starting permutation: s1a s3a s1a s3b
+step s1a: 
+    SELECT CURRENT_USER;
+    SHOW search_path;
+    SELECT t FROM x;
+
+current_user    
+----------------
+regress_sp_user1
+(1 row)
+
+search_path               
+--------------------------
+"$user", regress_sp_public
+(1 row)
+
+t                         
+--------------------------
+data in regress_sp_user1.x
+(1 row)
+
+step s3a: 
+    ALTER SCHEMA regress_sp_user1 RENAME TO regress_sp_user2;
+
+step s1a: 
+    SELECT CURRENT_USER;
+    SHOW search_path;
+    SELECT t FROM x;
+
+current_user    
+----------------
+regress_sp_user1
+(1 row)
+
+search_path               
+--------------------------
+"$user", regress_sp_public
+(1 row)
+
+t                          
+---------------------------
+data in regress_sp_public.x
+(1 row)
+
+step s3b: 
+    ALTER SCHEMA regress_sp_user2 RENAME TO regress_sp_user1;
+

src/test/isolation/isolation_schedule

@@ -100,3 +100,4 @@ test: truncate-conflict
 test: serializable-parallel
 test: serializable-parallel-2
 test: serializable-parallel-3
+test: search-path-inval

src/test/isolation/specs/search-path-inval.spec

@@ -0,0 +1,59 @@
+# Test search_path invalidation.
+
+setup
+{
+    CREATE USER regress_sp_user1;
+    CREATE SCHEMA regress_sp_user1 AUTHORIZATION regress_sp_user1;
+    CREATE SCHEMA regress_sp_public;
+    GRANT ALL PRIVILEGES ON SCHEMA regress_sp_public TO regress_sp_user1;
+}
+
+teardown
+{
+    DROP SCHEMA regress_sp_public CASCADE;
+    DROP SCHEMA regress_sp_user1 CASCADE;
+    DROP USER regress_sp_user1;
+}
+
+session s1
+setup
+{
+    SET search_path = "$user", regress_sp_public;
+    SET SESSION AUTHORIZATION regress_sp_user1;
+    CREATE TABLE regress_sp_user1.x(t) AS SELECT 'data in regress_sp_user1.x';
+    CREATE TABLE regress_sp_public.x(t) AS SELECT 'data in regress_sp_public.x';
+}
+step s1a
+{
+    SELECT CURRENT_USER;
+    SHOW search_path;
+    SELECT t FROM x;
+}
+
+session s2
+step s2a
+{
+    ALTER ROLE regress_sp_user1 RENAME TO regress_sp_user2;
+}
+step s2b
+{
+    ALTER ROLE regress_sp_user2 RENAME TO regress_sp_user1;
+}
+
+session s3
+step s3a
+{
+    ALTER SCHEMA regress_sp_user1 RENAME TO regress_sp_user2;
+}
+step s3b
+{
+    ALTER SCHEMA regress_sp_user2 RENAME TO regress_sp_user1;
+}
+
+# s1's search_path is invalidated by role name change in s2a, and
+# falls back to regress_sp_public.x
+permutation s1a s2a s1a s2b
+
+# s1's search_path is invalidated by schema name change in s2b, and
+# falls back to regress_sp_public.x
+permutation s1a s3a s1a s3b