planner: substitute merged DML IN/NOT IN subqueries via ListArg placeholder

[arthurschreiber]

Description

When an UPDATE SET expression contains an IN/NOT IN subquery whose routing is compatible with the outer route, the planner merges the subquery into the outer route — but the merge-time AST rewrite only substituted back *sqlparser.Argument placeholders, never sqlparser.ListArg. DML SET expressions placeholder IN/NOT IN subqueries with ListArg (a distinct AST type), so the placeholder leaked into the emitted SQL with no UncorrelatedSubquery primitive above to back it. Sending such a plan to vttablet would fail with missing bind var __sqN.

The fix adds a case sqlparser.ListArg arm to the type switch in rewriteMergedSubqueryExpr (go/vt/vtgate/planbuilder/operators/subquery_planning.go) mirroring the existing *Argument branch — the same cursor.Replace(sq.originalSubquery) path then substitutes the original inline subquery, matching the shape that DELETE … WHERE col = (1 in (select …)) already produces.

Two regression cases are added to dml_cases.json covering UPDATE+IN and UPDATE+NOT IN with merge-compatible routing. The existing UPDATE: same subquery as scalar SET and IN SET case targets user_extra inside a user update, so the routes don't merge and the bug couldn't surface there.

Adjacent rewrite paths (Ordering.settleOrderingExpressions, projection pe.Original) were intentionally left alone — isDML=true is only set in update.go for SET expressions, so a ListArg placeholder cannot reach those paths under any current call graph.

Related Issue(s)

Fixes #19965

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

None — purely planner-level correctness fix. No previously-working query shape changes plan; the affected shape (DML SET with merge-compatible IN/NOT IN subquery) was emitting a broken plan that would have failed at vttablet, so no production deployments are exercising it today.

AI Disclosure

Most of this was written by Claude Code — I just provided direction.

[vitess-bot]

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[Copilot]

Pull request overview

Fixes a vtgate planner correctness bug where merged IN/NOT IN subqueries inside UPDATE ... SET could leave behind a ListArg placeholder (e.g. ::__sqN) in the emitted SQL, causing execution-time failures due to missing bind vars.

Changes:

• Extend rewriteMergedSubqueryExpr to also recognize and rewrite sqlparser.ListArg placeholders when substituting merged subqueries back inline.
• Add regression plan-test cases covering UPDATE ... SET with merge-compatible IN and NOT IN subqueries.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
go/vt/vtgate/planbuilder/operators/subquery_planning.go	Add sqlparser.ListArg handling so merged DML IN/NOT IN placeholders are rewritten back to the original inline subquery.
go/vt/vtgate/planbuilder/testdata/dml_cases.json	Add regression cases ensuring UPDATE ... SET merged IN/NOT IN subqueries no longer emit ::__sqN.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.47%. Comparing base (70c7a72) to head (7e6fa5e).
⚠️ Report is 222 commits behind head on main.

Files with missing lines	Patch %	Lines
.../vtgate/planbuilder/operators/subquery_planning.go	0.00%	3 Missing ⚠️

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Flag	BASE (70c7a72)	HEAD (7e6fa5e)
	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #19973       +/-   ##
===========================================
- Coverage   69.67%    3.47%   -66.20%     
===========================================
  Files        1614       60     -1554     
  Lines      216793     9758   -207035     
===========================================
- Hits       151044      339   -150705     
+ Misses      65749     9419    -56330     

Flag	Coverage Δ
partial	3.47% <0.00%> (?)

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[mattlord]

LGTM! ❤️