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C++: Ignore compiler-generated variables in unused-static-variable query - #22961
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Extend the unused static variable query test with a minimal variadic sum instantiated with empty and non-empty packs. Record the spurious alert on the compiler-generated empty-pack variable reported in #22931. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Exclude synthetic variables from cpp/unused-static-variable so empty parameter pack placeholders do not trigger alerts. Update the regression expectation and document the analysis change. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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jketema
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October 30, 2026 15:09
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🟢 Approval recommended
No active review issues are reported, and the change targets false positives with corresponding regression coverage and documentation.
No open issues 🎉
What changed in this PR
Updates cpp/unused-static-variable to ignore compiler-generated variables, preventing false positives for synthetic placeholders created for empty abbreviated parameter packs.
Changes:
- Adds a C++20 regression test for empty and nonempty abbreviated parameter packs.
- Excludes compiler-generated variables from the unused-static-variable query.
- Adds a minor analysis change note.
| File | Description |
|---|---|
cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/test.cpp |
Adds a C++20 regression case for abbreviated parameter packs. |
cpp/ql/src/change-notes/2026-10-30-unused-static-compiler-generated.md |
Documents the query behavior change. |
cpp/ql/src/Best Practices/Unused Entities/UnusedStaticVariables.ql |
Filters compiler-generated variables from query results. |
Review effort: Lite (auto)
geoffw0
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Oct 30, 2026
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LGTM, but please check any result changes on DCA look reasonable before merging. 👍
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Yup, will not merge until I've seen that the DCA results are good. |
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DCA was uneventful. |
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Fixes #22931.
Exclude compiler-generated variables from
cpp/unused-static-variable. Our frontend creates a synthetic static variable as a placeholder for an empty function parameter pack; it is not user-declared storage and should not trigger an unused-variable alert.The first commit adds a minimal reproducer to the existing
UnusedStaticVariablestest, capturing the spurious alert. The second commit adds the exclusion, updates the expected result, and includes a change note.