MDEV-40274 Server aborts while reloading the table after failed DISCARD TABLESPACE

Problem:
========
row_discard_tablespace() updates SYS_TABLES, SYS_INDEXES and
reassigns the table identifier in SYSTEM TABLES.
These changes cannot be rolled back, and
row_discard_tablespace_for_mysql() commits the transaction even when
row_discard_tablespace() returned an error.
If the reassignment in row_mysql_table_id_reassign() fails
in the middle then the committed data dictionary is inconsistent
and the table can no longer be loaded from it, while the
in-memory table definition stays in the dictionary cache and
remains usable.

Solution:
=========
row_discard_tablespace_for_mysql(): If row_discard_tablespace()
failed, flag the table as corrupted and report the data dictionary
inconsistency in the error log.

dict_table_open_on_name(): Check dict_table_t::space before reading
fil_space_t::get_compression_algo() from it.

mysql-test/suite/innodb/r/innodb-virtual-columns.result

@@ -388,3 +388,20 @@ CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
 DROP TABLE t1;
+#
+# MDEV-40274 Server aborts while reloading the table after
+#     DISCARD TABLESPACE
+#
+call mtr.add_suppression("InnoDB: DISCARD TABLESPACE of table `test`\\.`t1` failed");
+call mtr.add_suppression("InnoDB: Table `test`\\.`t1` is corrupted");
+call mtr.add_suppression("Table `test`\\.`t1` is corrupted");
+CREATE TABLE t1(c1 INT) ENGINE=InnoDB;
+SET STATEMENT debug_dbug='+d,row_ins_sec_index_entry_timeout' FOR
+ALTER TABLE t1 DISCARD TABLESPACE;
+ERROR HY000: Got error 168 "Unknown (generic) error from engine" from storage engine InnoDB
+ALTER TABLE t1 ADD COLUMN cg16 INT AS(c1) VIRTUAL;
+ERROR 42000: Can't open table
+FLUSH TABLES;
+SELECT * FROM t1;
+ERROR HY000: Table `test`.`t1` is corrupted. Please drop the table and recreate.
+DROP TABLE t1;

mysql-test/suite/innodb/t/innodb-virtual-columns.test

@@ -363,3 +363,23 @@ SET GLOBAL innodb_max_purge_lag_wait=0;
 
 CHECK TABLE t1 EXTENDED;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-40274 Server aborts while reloading the table after
+--echo #     DISCARD TABLESPACE
+--echo #
+
+call mtr.add_suppression("InnoDB: DISCARD TABLESPACE of table `test`\\.`t1` failed");
+call mtr.add_suppression("InnoDB: Table `test`\\.`t1` is corrupted");
+call mtr.add_suppression("Table `test`\\.`t1` is corrupted");
+
+CREATE TABLE t1(c1 INT) ENGINE=InnoDB;
+--error ER_GET_ERRNO
+SET STATEMENT debug_dbug='+d,row_ins_sec_index_entry_timeout' FOR
+ALTER TABLE t1 DISCARD TABLESPACE;
+--error ER_CHECK_NO_SUCH_TABLE
+ALTER TABLE t1 ADD COLUMN cg16 INT AS(c1) VIRTUAL;
+FLUSH TABLES;
+--error ER_TABLE_CORRUPT
+SELECT * FROM t1;
+DROP TABLE t1;

storage/innobase/dict/dict0dict.cc

@@ -1038,7 +1038,8 @@ dict_table_open_on_name(
       if (!(ignore_err & ~DICT_ERR_IGNORE_FK_NOKEY) &&
           !table->is_readable() && table->corrupted)
       {
-        ulint algo= table->space->get_compression_algo();
+        const ulint algo= table->space
+          ? table->space->get_compression_algo() : ULINT_UNDEFINED;
         if (algo <= PAGE_ALGORITHM_LAST && !fil_comp_algo_loaded(algo))
           my_printf_error(ER_PROVIDER_NOT_LOADED,
                           "Table %`.*s.%`s is compressed with %s,"

storage/innobase/row/row0mysql.cc

@@ -2460,6 +2460,19 @@ rollback:
   table->space= nullptr;
   table->flags2|= DICT_TF2_DISCARDED;
   err= row_discard_tablespace(trx, table);
+  if (UNIV_UNLIKELY(err != DB_SUCCESS))
+  {
+    /* In case of error, table cannot be loaded from the data
+    dictionary any longer. Flag the table as corrupted, so that no
+    operation other than DROP TABLE will be attempted on it. */
+    table->corrupted= true;
+    ib::error() << "DISCARD TABLESPACE of table " << table->name
+                << " failed: " << ut_strerr(err)
+                << "; the data dictionary is now inconsistent. Please"
+                   " DROP TABLE " << table->name
+                << " and restore it from a backup.";
+  }
+
   DBUG_EXECUTE_IF("ib_discard_before_commit_crash",
                   log_buffer_flush_to_disk(); DBUG_SUICIDE(););
   /* FTS_ tables may be deleted */