MDEV-29978 Corruption errors upon CHECK on temporary InnoDB table

row_check_index(): Treat secondary indexes of temporary tables as if
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
is in effect. That is, only consider the delete-mark and nothing else.

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

@@ -789,4 +789,16 @@ CHECK TABLE t EXTENDED;
 Table	Op	Msg_type	Msg_text
 test.t	check	status	OK
 DROP TEMPORARY TABLE t;
+#
+# MDEV-29978 Corruption errors upon CHECK on temporary InnoDB table
+#
+CREATE TEMPORARY TABLE t (f INT UNIQUE) ENGINE=InnoDB;
+INSERT INTO t (f) VALUES (1),(2);
+CHECK TABLE t;
+Table	Op	Msg_type	Msg_text
+test.t	check	status	OK
+CHECK TABLE t EXTENDED;
+Table	Op	Msg_type	Msg_text
+test.t	check	status	OK
+DROP TEMPORARY TABLE t;
 # End of 10.6 tests

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

@@ -624,4 +624,15 @@ UPDATE t SET a=2;
 CHECK TABLE t;
 CHECK TABLE t EXTENDED;
 DROP TEMPORARY TABLE t;
+
+--echo #
+--echo # MDEV-29978 Corruption errors upon CHECK on temporary InnoDB table
+--echo #
+
+CREATE TEMPORARY TABLE t (f INT UNIQUE) ENGINE=InnoDB;
+INSERT INTO t (f) VALUES (1),(2);
+CHECK TABLE t;
+CHECK TABLE t EXTENDED;
+DROP TEMPORARY TABLE t;
+
 --echo # End of 10.6 tests

storage/innobase/row/row0sel.cc

@@ -6300,14 +6300,16 @@ dberr_t row_check_index(row_prebuilt_t *prebuilt, ulint *n_rows)
     goto next_rec;
   }
 
-  if (index->is_clust())
+  if (prebuilt->table->is_temporary())
   {
-    if (prebuilt->trx->isolation_level == TRX_ISO_READ_UNCOMMITTED)
-    {
-      if (!rec_deleted)
-        goto count_row;
+  count_or_not:
+    if (rec_deleted)
       goto next_rec;
-    }
+  }
+  else if (index->is_clust())
+  {
+    if (prebuilt->trx->isolation_level == TRX_ISO_READ_UNCOMMITTED)
+      goto count_or_not;
 
     trx_id_t rec_trx_id= row_get_rec_trx_id(rec, index, offsets);
 
@@ -6371,10 +6373,7 @@ dberr_t row_check_index(row_prebuilt_t *prebuilt, ulint *n_rows)
                           ER_NOT_KEYFILE, "InnoDB: %s", w.m_oss.str().c_str());
     }
 
-    if (!rec_deleted)
-      goto count_row;
-
-    goto next_rec;
+    goto count_or_not;
   }
   else if (const trx_id_t page_trx_id= page_get_max_trx_id(page_align(rec)))
   {