expression: fix unexpected panic when doing isNullRejected check (#22173)

[ti-srebot]

cherry-pick #22173 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr 22327

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/22327:ti-srebot:release-4.0-cdcb0ffa3412

---

What problem does this PR solve?

Issue Number: close #22098

Problem Summary:
TiDB server panics when executing a prepared SQL with prepared-plan-cache enabled.

What is changed and how it works?

What's Changed:
When creating Constant in foldConstant for NullRejectCheck case, we set its DeferredExpr to nil.

How it Works:

1. The panic is caused by reevaluating DeferredExpr of the constant created in foldConstant. When creating the constant in foldConstant, we evaluate a dummyScalarFunc instead of the original ScalarFunction to get the constant value while we set DeferredExpr to the original ScalarFunction. When the constant is used as argument for another function, it is reevaluated by evaluating the original ScalarFunction, which cannot be done in the context and leads to panic.
2. The constant mentioned above is created to compose the result expression of EvaluateExprWithNull when InNullRejectCheck = true. We just check whether the result expression is null or false and then let it die. Basically, the constant is used once briefly and will not be retained for a long time. Hence setting DeferredExpr of the constant to nil is ok.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Release note

• fix unexpected panic when executing certain prepared SQL with prepared-plan-cache enabled.

[ti-srebot]

/run-all-tests

[ti-srebot]

@xuyifangreeneyes you're already a collaborator in bot's repo.

[xuyifangreeneyes]

/run-all-tests

[xuyifangreeneyes]

/run-all-tests

[xuyifangreeneyes]

/run-all-tests

[winoros]

lgtm

[qw4990]

LGTM