expression: fix signed bigint subtraction overflow | tidb-test=pr/2742

[hawkingrei]

What problem does this PR solve?

Issue Number: close #67211

Problem Summary:

Signed BIGINT subtraction missed the 0 - math.MinInt64 overflow boundary. TiDB could return -9223372036854775808 without warnings for (0) - a when a was -9223372036854775808, while MySQL reports an out-of-range error.

What changed and how does it work?

The signed/signed integer subtraction overflow check now treats zero the same as other non-negative left operands when subtracting a negative right operand. This preserves in-range cases such as -1 - math.MinInt64 while raising overflow for 0 - math.MinInt64.

Regression coverage was added for both row-based and vectorized BIGINT subtraction evaluation.

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.

Unit test:

./tools/check/failpoint-go-test.sh pkg/expression -run 'TestArithmeticMinus|TestVectorizedDecimalErrOverflow' -count=1
make lint

Manual test:

• Replayed the issue SQL locally with a temporary testkit harness before and after the fix.
• Before the fix, (0) - a returned -9223372036854775808 without warnings.
• After the fix, (0) - a and (1) - a return error 1690, while (-1) - a still returns 9223372036854775807.

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.

Fix an issue where signed BIGINT subtraction could silently overflow for `0 - -9223372036854775808` instead of returning an out-of-range error.

Summary by CodeRabbit

• Bug Fixes

  • Adjusted overflow detection logic for integer subtraction when the first operand equals zero.

• Tests

  • Added comprehensive test cases covering integer subtraction boundary conditions with minimum integer values.
  • Added vectorized operation tests for integer subtraction overflow scenarios.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Details

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR fixes a silent overflow bug where (0) - BIGINT_MIN fails to raise an out-of-range error. The fix adjusts the overflow-detection condition in builtinArithmeticMinusIntSig to include zero, and adds scalar and vectorized test coverage validating the corrected behavior across both evaluation paths.

Changes

BIGINT minus overflow edge case

Layer / File(s)	Summary
Overflow detection fix and test coverage pkg/expression/builtin_arithmetic.go, pkg/expression/builtin_arithmetic_test.go, pkg/expression/builtin_arithmetic_vec_test.go	The overflowCheck condition changes from a > 0 && b < 0 to a >= 0 && b < 0, treating zero as a boundary case. Scalar tests verify that (0) - BIGINT_MIN and other edge cases correctly raise errors or return expected results. Vectorized tests confirm the same behavior in columnar evaluation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested labels

approved, lgtm

Suggested reviewers

• windtalker
• qw4990

Poem

🐰 A zero minus the coldest of ints,
Now properly warns of its borderline hints,
No silent overflow in the night,
With tests to confirm every edge is right!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The PR description follows the required template, includes the issue link, problem summary, explanation of changes, test checklist with selections, and release notes.
Linked Issues check	✅ Passed	The code changes directly address issue #67211 by fixing the overflow detection for 0 - math.MinInt64 in signed BIGINT subtraction, with corresponding test coverage.
Out of Scope Changes check	✅ Passed	All changes are focused on fixing the signed BIGINT subtraction overflow bug: adjusting overflow logic, adding test cases for MININT64 scenarios, and documenting boundary behavior.
Title check	✅ Passed	The title clearly identifies the specific change: a fix for signed bigint subtraction overflow, matching the core objective of handling the 0 - MinInt64 boundary case.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.4914%. Comparing base (6a6eefe) to head (1bdc13d).

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #68441        +/-   ##
================================================
- Coverage   77.2762%   76.4914%   -0.7849%     
================================================
  Files          2010       1992        -18     
  Lines        555477     557613      +2136     
================================================
- Hits         429252     426526      -2726     
- Misses       125305     131043      +5738     
+ Partials        920         44       -876     

Flag	Coverage Δ
integration	41.5383% <100.0000%> (+1.7442%)	⬆️

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

Components	Coverage Δ
dumpling	60.4888% <ø> (ø)
parser	∅ <ø> (∅)
br	49.9725% <ø> (-13.0354%)	⬇️

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[hawkingrei]

/retest-required