result: don't panic when affectedRows/insertIds are empty

[c-tonneslan]

Closes #1733.

mysqlResult.LastInsertId / RowsAffected indexed into their slices without checking length, so any code path that left the slices empty (e.g. an error before the affected-rows packet) panicked the caller. Return 0, nil instead, which matches the database/sql.Result contract for "no rows affected".

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

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Run ID: be13f3c9-1584-4c4d-87e7-55b9e0697805

📥 Commits

Reviewing files that changed from the base of the PR and between a065b60 and ef5b26a.

📒 Files selected for processing (2)

• result.go
• result_test.go

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Walkthrough

This PR fixes a panic in LastInsertId() when called on an empty result by adding a defensive check for empty insertIds slice. The method now returns (0, nil) early instead of unconditionally indexing into the slice. A regression test TestEmptyResult verifies both LastInsertId() and RowsAffected() return zero values safely on empty results.

Changes

Empty result panic fix

Layer / File(s)	Summary
Empty result handling and test coverage result.go, result_test.go	LastInsertId() adds an early return for empty insertIds, replacing unsafe slice indexing. TestEmptyResult regression test validates that both LastInsertId() and RowsAffected() return zero values without error when called on an empty result.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: preventing panics in affectedRows/insertIds when slices are empty, which is the core issue being fixed.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem (panic from unchecked slice access) and the solution (returning 0, nil for empty slices).
Linked Issues check	✅ Passed	The PR directly addresses issue #1733 by adding length checks to prevent panics in RowsAffected and LastInsertId when slices are empty, matching the linked issue's requirement.
Out of Scope Changes check	✅ Passed	All changes are in-scope: the slice-length safety checks in result.go and the regression test in result_test.go directly address the panic issue without introducing unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

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[shogo82148]

Please provide reproducible steps for users.

[coveralls]

coverage: 82.718% (+0.02%) from 82.701% — c-tonneslan:fix/result-empty-slice-panic into go-sql-driver:master

[c-tonneslan]

Honestly, I went hunting for a real user-level repro on master and I can't get there. Every path that returns a result goes through readResultSetHeaderPacket first, which appends to both slices before any error check, so by the time RowsAffected runs the slices are length >= 1.

The #1733 report is on v1.8.0 and the stack doesn't show how the conn ended up with empty slices, so I can't put a faithful repro in the test. I'll close this and defer to you and @methane on whether the guard is worth adding without one.