expression: fix IS_IPV4_COMPAT for all-zero address

[hawkingrei]

What problem does this PR solve?

Issue Number: close #59458

Problem Summary:

IS_IPV4_COMPAT(X'00000000000000000000000000000000') returned 1, while MySQL-compatible behavior expects 0 for the all-zero IPv6 unspecified address.

What changed and how does it work?

This PR adds a shared IS_IPV4_COMPAT binary classifier for both scalar and vectorized evaluation.

The function still requires a 16-byte IPv6 value with a zero 12-byte prefix, but it now rejects the all-zero address by requiring at least one non-zero byte in the embedded IPv4 suffix.

Check List

Tests

• Unit test
  • ./tools/check/failpoint-go-test.sh pkg/expression -run TestIsIPv4Compat -count=1
  • ./tools/check/failpoint-go-test.sh pkg/expression -run TestVectorizedBuiltinMiscellaneousFunc -count=1 -args builtinIsIPv4CompatSig
• Integration test
  • ./tools/check/failpoint-go-test.sh pkg/expression/integration_test -run TestVectorMiscFunctions -count=1
  • git diff --check -- pkg/expression/builtin_miscellaneous.go pkg/expression/builtin_miscellaneous_vec.go pkg/expression/builtin_miscellaneous_test.go pkg/expression/builtin_miscellaneous_vec_test.go pkg/expression/integration_test/integration_test.go
  • make lint
• 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.

Fix `IS_IPV4_COMPAT` to return `0` for the all-zero IPv6 address.

Summary by CodeRabbit

• Bug Fixes
  • Improved IS_IPV4_COMPAT function behavior. The all-zero IPv6 unspecified address is now correctly classified as not IPv4-compatible, returning 0 instead of the previous incorrect result. This fixes edge case handling in IPv6 address validation.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 5b9b2f12-ac1b-4d96-901c-e7608bab23ef

📥 Commits

Reviewing files that changed from the base of the PR and between 6a6eefe and 90b6864.

📒 Files selected for processing (5)

• pkg/expression/builtin_miscellaneous.go
• pkg/expression/builtin_miscellaneous_test.go
• pkg/expression/builtin_miscellaneous_vec.go
• pkg/expression/builtin_miscellaneous_vec_test.go
• pkg/expression/integration_test/integration_test.go

---

📝 Walkthrough

Walkthrough

The IS_IPV4_COMPAT function is corrected to return 0 for the all-zero IPv6 address (::) instead of 1. A new helper function isIPv4CompatBinary consolidates the compatibility check logic for both scalar and vectorized evaluation, and comprehensive test coverage validates the fix across all evaluation paths.

Changes

IPv4-compat all-zero address fix

Layer / File(s)	Summary
IPv4-compat helper and scalar evaluation pkg/expression/builtin_miscellaneous.go	New isIPv4CompatBinary helper checks IPv6 byte length, verifies the first 12 bytes are zero, and treats the all-zero address as not IPv4-compatible. builtinIsIPv4CompatSig.evalInt replaces inline prefix logic with calls to the helper.
Vectorized evaluation update pkg/expression/builtin_miscellaneous_vec.go	builtinIsIPv4CompatSig.vecEvalInt removes local prefixCompat setup and manual prefix/length checks, delegating to isIPv4CompatBinary in the per-row loop condition.
Test coverage for all-zero address case pkg/expression/builtin_miscellaneous_test.go, pkg/expression/builtin_miscellaneous_vec_test.go, pkg/expression/integration_test/integration_test.go	Unit, vectorized, and integration tests all verify that the all-zero IPv6 address input returns 0, covering scalar evaluation, vectorized batches, and end-to-end queries.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A zero address dared to deceive,
But our helper now makes it quite clear:
IPv6's all-zeros shall not make us believe—
False it returns, the fix drawing near! ✨

🚥 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
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing IS_IPV4_COMPAT function behavior for the all-zero address case.
Description check	✅ Passed	The description includes the required issue reference (#59458), problem summary, implementation explanation, comprehensive test coverage (unit and integration), release notes, and documentation flags.
Linked Issues check	✅ Passed	The PR directly addresses issue #59458 by implementing the exact fix required: IS_IPV4_COMPAT now returns 0 for the all-zero IPv6 address instead of 1, matching MySQL behavior.
Out of Scope Changes check	✅ Passed	All changes are focused on fixing the IS_IPV4_COMPAT function across scalar, vectorized, and test implementations, with no unrelated modifications.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[codecov]

Codecov Report

❌ Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.4894%. Comparing base (6a6eefe) to head (90b6864).

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #68438        +/-   ##
================================================
- Coverage   77.2762%   76.4894%   -0.7869%     
================================================
  Files          2010       1992        -18     
  Lines        555477     557618      +2141     
================================================
- Hits         429252     426519      -2733     
- Misses       125305     131054      +5749     
+ Partials        920         45       -875     

Flag	Coverage Δ
integration	41.5432% <73.3333%> (+1.7492%)	⬆️

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

[hawkingrei]

/retest-required