fsp0fsp.cc: log unexpected table in sys tablespace

Fix log message about unexpected table in system tablespace as the current
message can be missleading due to still existing (but already deprecated)
system tables SYS_DATAFILES and SYS_TABLESPACES, reported in
 - MDEV-38412

Also adding the informative message with table name of the unexpected table
in system table space.

Author: jendis

mysql-test/suite/innodb/r/sys_defragment_fail.result

@@ -17,7 +17,8 @@ INSERT INTO t1 SELECT seq, seq FROM seq_1_to_4096;
 DROP TABLE t2;
 InnoDB		0 transactions not purged
 # restart
-FOUND 1 /InnoDB: User table exists in the system tablespace/ in mysqld.1.err
+FOUND 1 /InnoDB: Found unexpected table in system tablespace: test\/t1/ in mysqld.1.err
+FOUND 1 /InnoDB: Unexpected table exists in the system tablespace/ in mysqld.1.err
 DROP TABLE t1;
 InnoDB		0 transactions not purged
 # restart: --debug_dbug=+d,fail_after_level_defragment

mysql-test/suite/innodb/t/sys_defragment_fail.test

@@ -29,7 +29,9 @@ let $restart_parameters=;
 --source include/restart_mysqld.inc
 
 let SEARCH_FILE= $MYSQLTEST_VARDIR/log/mysqld.1.err;
-let SEARCH_PATTERN=InnoDB: User table exists in the system tablespace;
+let SEARCH_PATTERN=InnoDB: Found unexpected table in system tablespace: test\/t1;
+--source include/search_pattern_in_file.inc
+let SEARCH_PATTERN=InnoDB: Unexpected table exists in the system tablespace;
 --source include/search_pattern_in_file.inc
 DROP TABLE t1;
 

storage/innobase/fsp/fsp0fsp.cc

@@ -5723,6 +5723,14 @@ static dberr_t user_tables_exists() noexcept
       goto corrupt;
     if (!dict_sys.is_sys_table(mach_read_from_8(field)))
     {
+      const byte *name_field = rec_get_nth_field_old(
+        rec, DICT_FLD__SYS_TABLES__NAME, &len);
+      if (len != UNIV_SQL_NULL && len > 0)
+      {
+        sql_print_information(
+          "InnoDB: Found unexpected table in system tablespace: %.*s",
+          (int)len, (const char *)name_field);
+      }
       err= DB_SUCCESS_LOCKED_REC;
       btr_pcur_close(&pcur);
       goto func_exit;
@@ -5740,7 +5748,7 @@ dberr_t fil_space_t::defragment() noexcept
   if (err == DB_SUCCESS_LOCKED_REC)
   {
     sql_print_information(
-      "InnoDB: User table exists in the system tablespace."
+      "InnoDB: Unexpected table exists in the system tablespace."
       "Please try to move the data from system tablespace "
       "to separate tablespace before defragment the "
       "system tablespace.");