Improve ALTER POLICY tab completion.

Complete "ALTER POLICY" with a policy name, as we do for DROP POLICY.
And, complete "ALTER POLICY polname ON" with a table name that has such
a policy, as we do for DROP POLICY, rather than with any table name
at all.

Masahiko Sawada

src/bin/psql/tab-complete.c

@@ -1459,6 +1459,10 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH_LIST(list_ALTERMATVIEW);
 	}
 
+	/* ALTER POLICY <name> */
+	else if (pg_strcasecmp(prev2_wd, "ALTER") == 0 &&
+			 pg_strcasecmp(prev_wd, "POLICY") == 0)
+		COMPLETE_WITH_QUERY(Query_for_list_of_policies);
 	/* ALTER POLICY <name> ON */
 	else if (pg_strcasecmp(prev3_wd, "ALTER") == 0 &&
 			 pg_strcasecmp(prev2_wd, "POLICY") == 0)
@@ -1467,7 +1471,10 @@ psql_completion(const char *text, int start, int end)
 	else if (pg_strcasecmp(prev4_wd, "ALTER") == 0 &&
 			 pg_strcasecmp(prev3_wd, "POLICY") == 0 &&
 			 pg_strcasecmp(prev_wd, "ON") == 0)
-		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_tables, NULL);
+	{
+		completion_info_charp = prev2_wd;
+		COMPLETE_WITH_QUERY(Query_for_list_of_tables_for_policy);
+	}
 	/* ALTER POLICY <name> ON <table> - show options */
 	else if (pg_strcasecmp(prev5_wd, "ALTER") == 0 &&
 			 pg_strcasecmp(prev4_wd, "POLICY") == 0 &&