expression: fix a bug caused by cast function signature wrong in aggregation push down (#28805)

[ti-srebot]

cherry-pick #28805 to release-5.2
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/29345

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---

What problem does this PR solve?

Issue Number: close #28804

Problem Summary:

What is changed and how it works?

Remove the special handle of cast function in ColumnSubstituteImpl

The bug is caused by this:

Before ColumnSubstitute, the function signature of cast(floor(hour(ts) / 4) as char) is cast(Int -> Varstring) ...
Then, the ColumnSubstitute will substitute the column ts of expression floor(hour(ts) / 4)
After that, the expression floor(hour(ts) / 4) signature changed, it's return type is not Int any more.
Expression floor(hour(ts) / 4) returns Decimal instead.

But the signature of cast() function is still cast(Int -> Varstring), so the cast expect floor(hour(ts) / 4) to return Int and the later returns Decimal, the error is throw finally.

What's Changed:

Remove the special handle of the cast function.

How it Works:

The bug is caused by the special handle of the Cast function.
Its function args are re-generated (signature re-calculated), but the Cast function it self does not refresh.
So the signature mismatch...

OK, "why the signature change from Int to Decimal" is another story, it's caused by the wrong Flen and that's another big issue.
I'm not meant to solve it here.

Check List

Tests

• [] Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Fix `ColumnSubstitute` cause wrong signature of the Cast() function, this bug could led TiDB return "baseBuiltinFunc.vecEvalInt() should never be called" error in some aggregation push down scenario.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• guo-shaoge
• wjhuang2016

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[ti-srebot]

/run-all-tests

[ti-srebot]

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

[VelocityLight]

This pull request is closed because it's related version has closed automatic cherry-picking.
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• https://internals.tidb.io/t/topic/785