expression: Fix warnings for FORMAT() in CTE

[dveeden]

What problem does this PR solve?

Issue Number: close #56193

Problem Summary:

This fixes the corrupt warnings. It doesn't fix the difference in the number of warnings between MySQL and TiDB.

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

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

Please refer to Release Notes Language Style Guide to write a quality release note.

Fixes corrupt warnings generated by the FORMAT() function within a CTE

[tiprow]

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[dveeden]

The GetString() function:

tidb/pkg/util/chunk/column.go

Lines 653 to 656 in 5ead7e9

	// GetString returns the string in the specific row.
	func (c *Column) GetString(rowID int) string {
	return string(hack.String(c.data[c.offsets[rowID]:c.offsets[rowID+1]]))
	}

It relies on hack.String():

tidb/pkg/util/hack/hack.go

Lines 26 to 34 in 5ead7e9

	// String converts slice to MutableString without copy.
	// The MutableString can be converts to string without copy.
	// Use it at your own risk.
	func String(b []byte) MutableString {
	if len(b) == 0 {
	return ""
	}
	return MutableString(unsafe.String(unsafe.SliceData(b), len(b)))
	}

This doesn't seem to be safe in this case as warnings are added to h.warnings correctly, but then the arguments are corrupt when GetWarnings() is called.

[dveeden]

/ok-to-test

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 77.2758%. Comparing base (281462c) to head (0d204aa).
Report is 50 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #56198        +/-   ##
================================================
+ Coverage   73.3745%   77.2758%   +3.9013%     
================================================
  Files          1602       1641        +39     
  Lines        444469     469113     +24644     
================================================
+ Hits         326127     362511     +36384     
+ Misses        98392      85333     -13059     
- Partials      19950      21269      +1319     

Flag	Coverage Δ
integration	53.8549% <50.0000%> (?)
unit	73.9513% <0.0000%> (+1.4798%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9478% <ø> (ø)
parser	∅ <ø> (∅)
br	61.1603% <ø> (+15.2707%)	⬆️

[dveeden]

/retest

[dveeden]

/retest

[dveeden]

/retest

[YangKeao]

LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-25 07:54:14.245110075 +0000 UTC m=+1638923.985534014: ☑️ agreed by YangKeao.
• 2024-09-26 08:52:24.015482252 +0000 UTC m=+1728813.755906192: ☑️ agreed by hawkingrei.

[windtalker]

lgtm

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, windtalker, YangKeao

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