planner: fix null-reject proof for WEEK and YEARWEEK

[winoros]

What problem does this PR solve?

Issue Number: close #68816

Problem Summary:

WEEK(date, mode) and YEARWEEK(date, mode) were classified as whole-function NULL-preserving builtins for null-reject proof. This is unsafe because TiDB/MySQL treats a NULL mode argument as mode 0, so predicates such as WEEK('2024-01-08', nullable_mode) >= 0 are not null-rejecting on nullable_mode.

What changed and how does it work?

• Remove WEEK and YEARWEEK from the whole-function NULL-preserving builtin table.
• Add a narrow proof rule that keeps the valid behavior for their date argument: if the date argument is proven NULL, the function result is NULL.
• Remove unreachable NULL-preserving table entries for builtins that are not registered as scalar functions.
• Extend the registry snapshot test to reject future NULL-preserving table entries that are not registered builtins, except for the internal scalar CAST.

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:

go test -count=1 -tags=intest,deadlock ./pkg/planner/util -run 'Test(IsNullRejectedProofModes|NullRejectBuiltinRegistrySnapshot)'

Other checks:

make lint
git diff --check origin/master..HEAD

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 a potential wrong result caused by unsafe null-reject proof for WEEK and YEARWEEK with a NULL mode argument.

Summary by CodeRabbit

• Bug Fixes

  • Corrected null-handling for WEEK and YEARWEEK date functions and refined which built-ins are treated as null-preserving to improve query accuracy.

• Tests

  • Expanded test coverage for null-rejection behavior, added registry presence checks for built-ins, and added datetime-focused cases to validate WEEK/YEARWEEK handling.

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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: 147cc68a-8aef-4a1a-a9d9-3ee22b60c5a1

📥 Commits

Reviewing files that changed from the base of the PR and between 43a335f and 9ee6612.

📒 Files selected for processing (3)

• pkg/planner/util/null_misc.go
• pkg/planner/util/null_misc_builtins.go
• pkg/planner/util/null_misc_test.go

💤 Files with no reviewable changes (1)

• pkg/planner/util/null_misc_builtins.go

🚧 Files skipped from review as they are similar to previous changes (2)

• pkg/planner/util/null_misc.go
• pkg/planner/util/null_misc_test.go

---

📝 Walkthrough

Walkthrough

The PR stops classifying WEEK and YEARWEEK as fully NULL-preserving, adds targeted proof logic that treats only the date argument as NULL-preserving, and expands tests and registry checks to validate the corrected null-rejection behavior.

Changes

WEEK/YEARWEEK null-handling fix

Layer / File(s)	Summary
Builtin NULL-preserving classification updates pkg/planner/util/null_misc_builtins.go	Removes ast.UnaryPlus and ast.Soundex from nullRejectNullPreservingFunctions; excludes WEEK(date, mode) and YEARWEEK(date, mode) from blanket null-preserving classification.
Special-case null-rejection proof for WEEK/YEARWEEK pkg/planner/util/null_misc.go	Adds switch cases in proveNullRejectedScalarFunc for ast.Week and ast.YearWeek that only treat the date argument as NULL-preserving; returns nonTrue+mustNull if the date is mustNull, otherwise yields no proof.
Extended tests for WEEK/YEARWEEK and builtin registry pkg/planner/util/null_misc_test.go	Validates registry membership for nullRejectNullPreservingFunctions entries (except ast.Cast); adds innerDate datetime column, WEEK/YEARWEEK expression builders and table-driven assertions, and a newNullRejectDatetimeColumn helper.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 The WEEK and YEARWEEK once took a fall,
Mode's NULL was blamed for dropping a row;
Now date-first proof keeps left-joins whole,
Tests sing the fix and registry rows glow. ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% 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	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'planner: fix null-reject proof for WEEK and YEARWEEK' directly summarizes the main change, which is fixing the null-reject proof behavior for these two functions.
Linked Issues check	✅ Passed	All code changes directly address the objectives in issue #68816: removing WEEK/YEARWEEK from NULL-preserving builtins table, adding targeted null-proof rule for date argument only, and extending registry validation.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the WEEK/YEARWEEK null-reject proof issue; removal of UnaryPlus and Soundex from the builtins map is a cleanup of unreachable entries.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-null-misc-builtin-classification

Warning

Tools execution failed with the following error:

Failed to run tools: 13 INTERNAL: Received RST_STREAM with code 2 (Internal server error)

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.3535%. Comparing base (7727603) to head (9ee6612).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #68817        +/-   ##
================================================
- Coverage   76.3106%   75.3535%   -0.9572%     
================================================
  Files          2041       2023        -18     
  Lines        563469     567153      +3684     
================================================
- Hits         429987     427370      -2617     
- Misses       132566     139752      +7186     
+ Partials        916         31       -885     

Flag	Coverage Δ
integration	41.3156% <0.0000%> (+1.5371%)	⬆️

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

Components	Coverage Δ
dumpling	60.4610% <ø> (ø)
parser	∅ <ø> (∅)
br	49.8023% <ø> (-13.0287%)	⬇️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, qw4990

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-05-31 11:11:33.850762382 +0000 UTC m=+94394.921079762: ☑️ agreed by hawkingrei.
• 2026-05-31 13:51:50.370433934 +0000 UTC m=+104011.440751314: ☑️ agreed by qw4990.

[ti-chi-bot]

@winoros: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	9ee6612	link	unknown	/test check-dev2

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