Bug#120948 Add removedLegacyHashingFunctions upgrade check for MySQL 9.7

[akshatnehra]

Description

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The MySQL Shell upgrade checker (util.checkForServerUpgrade()) does not detect usage of MD5(), SHA1(), or SHA() functions in database objects when upgrading from 8.4 to 9.6+. These functions were removed from the server binary in MySQL 9.6.0 and moved to component_classic_hashing.

The existing removedFunctions check is registered at version 8.0.11, so its version condition (8.0.11 > 8.4.x) evaluates to false and the check is skipped entirely for 8.4+ source versions. This leaves a gap: if a generated column within any table uses these functions and MySQL server is upgraded to 9.6.0 or later, the table stops working. The server does not re-validate stored generated column expressions during upgrade, and component_classic_hashing cannot help since loadable functions are disallowed in generated column expressions (ERROR 3763). The only recovery path is restoring from a pre-upgrade backup.

How to recreate the issue

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1. Set up a MySQL 8.4 server.
2. Create a table with a STORED generated column using MD5:

   CREATE TABLE t (id INT PRIMARY KEY, val VARCHAR(255),
     h VARCHAR(32) GENERATED ALWAYS AS (MD5(val)) STORED);
   INSERT INTO t VALUES (1, 'hello', DEFAULT);

3. Run util.checkForServerUpgrade() targeting 9.7.0:

   mysqlsh root@localhost --util check-for-server-upgrade --target-version=9.7.0
   

4. Observe that no error or warning is reported for the generated column.
5. Upgrade to MySQL 9.7.0.
6. Attempt any operation on the table:

   SELECT * FROM t;
   -- ERROR 3763 (HY000): Expression of generated column 'h' contains a disallowed function: md5.

The table is now permanently inaccessible and SELECT, INSERT, ALTER TABLE DROP COLUMN, SHOW CREATE TABLE, and TRUNCATE all fail with ERROR 3763.

Fix

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This patch adds a new removedLegacyHashingFunctions upgrade check that scans 8 object types for usage of the removed functions: views, stored routines, triggers, events, generated columns (STORED and VIRTUAL), CHECK constraints, DEFAULT expressions, and functional indexes.

Severity is split based on recoverability:

• ERROR for generated columns, functional indexes, CHECK constraints, and DEFAULT expressions as these either permanently brick the table or block the upgrade, and cannot be resolved by installing the component.
• WARNING for views, routines, triggers, and events as these can be resolved after upgrade by installing component_classic_hashing, or rewritten before upgrading.

The check is registered at version 9.6.0 so it fires for upgrades from 8.4+ to 9.6+

Testing

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• Tested against Docker MySQL 8.4.10 with all 10 object types: 5 errors, 5 warnings as expected.
• Verified actual upgrade behavior on MySQL 9.7:
  • Generated columns (STORED/VIRTUAL): ERROR 3763, even with component installed that confirms ERROR severity.
  • Functional indexes, CHECK constraints, DEFAULT expressions: server rejects creation that confirms ERROR severity.
  • Views, routines, triggers, events: work correctly after INSTALL COMPONENT 'file://component_classic_hashing' that confirms WARNING severity.

References

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• https://dev.mysql.com/doc/refman/9.7/en/legacy-hashing-component.html
• https://blogs.oracle.com/mysql/post/mysql-9-x-moving-away-from-sha1-and-md5

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This contribution is under the OCA signed by Amazon and covering submissions to the MySQL project.

[mysql-oca-bot]

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