https://github.com/voyager-jhk updated https://github.com/llvm/llvm-project/pull/199905
>From 215ae67adc0771903e6571b8797d6d85413ec3ff Mon Sep 17 00:00:00 2001 From: voyager-jhk <[email protected]> Date: Wed, 27 May 2026 16:54:08 +0800 Subject: [PATCH] [clang-tidy] Fix false positive in bugprone-use-after-move with std::forward on derived classes The `bugprone-use-after-move` check correctly identified partial moves when using `std::move` by matching the `ImplicitCastExpr` (DerivedToBase) as the parent of the call. However, when using `std::forward<Base>`, the cast occurs inside the argument, causing the matcher to miss the cast and falsely report a use-after-move. This patch manually checks the first argument of the moving call for a `DerivedToBase` cast if the parent matcher fails, ensuring both `move` and `forward` are correctly identified as partial moves. Fixes #63202 --- .../clang-tidy/bugprone/UseAfterMoveCheck.cpp | 8 ++++ clang-tools-extra/docs/ReleaseNotes.rst | 2 + .../checkers/bugprone/use-after-move.cpp | 42 +++++++++++++++++++ 3 files changed, 52 insertions(+) diff --git a/clang-tools-extra/clang-tidy/bugprone/UseAfterMoveCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/UseAfterMoveCheck.cpp index 361be321185df..1788c9a955322 100644 --- a/clang-tools-extra/clang-tidy/bugprone/UseAfterMoveCheck.cpp +++ b/clang-tools-extra/clang-tidy/bugprone/UseAfterMoveCheck.cpp @@ -650,6 +650,14 @@ void UseAfterMoveCheck::check(const MatchFinder::MatchResult &Result) { const CXXRecordDecl *MovedAs = ParentCast ? ParentCast->getType()->getAsCXXRecordDecl() : nullptr; + if (!MovedAs && CallMove && CallMove->getNumArgs() > 0) { + if (const auto *ArgCast = + dyn_cast<ImplicitCastExpr>(CallMove->getArg(0)->IgnoreParens())) { + if (ArgCast->getCastKind() == CK_DerivedToBase) + MovedAs = ArgCast->getType()->getAsCXXRecordDecl(); + } + } + for (Stmt *CodeBlock : CodeBlocks) { UseAfterMoveFinder Finder(Result.Context, InvalidationFunctions, ReinitializationFunctions, MovedAs); diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst index fa53072be1eac..88e3795e1aa15 100644 --- a/clang-tools-extra/docs/ReleaseNotes.rst +++ b/clang-tools-extra/docs/ReleaseNotes.rst @@ -457,6 +457,8 @@ Changes in existing checks `CheckedReturnTypes` option from :doc:`bugprone-unused-return-value <clang-tidy/checks/bugprone/unused-return-value>`, which caused false positives on functions returning ``std::error_code`` or similar types. + - Avoid false positives when forwarding derived objects to base class + initializers. - Improved :doc:`cppcoreguidelines-avoid-capturing-lambda-coroutines <clang-tidy/checks/cppcoreguidelines/avoid-capturing-lambda-coroutines>` diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/use-after-move.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/use-after-move.cpp index 0844aa32825f6..c9b307fd668b1 100644 --- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/use-after-move.cpp +++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/use-after-move.cpp @@ -1941,3 +1941,45 @@ void stdTieParenthesizedPartialReinit() { // CHECK-NOTES: [[@LINE-1]]:3: warning: 'a' used after it was moved // CHECK-NOTES: [[@LINE-5]]:3: note: move occurred here } +namespace GH63202 { + +struct Person { + std::string name; + Person() = default; + Person(Person&&) = default; + Person& operator=(Person&&) = default; +}; + +struct SpecialPerson : Person { + std::string surname; + + // Valid: partial move + SpecialPerson(SpecialPerson&& sp) + : Person(std::move(sp)), surname(std::move(sp.surname)) {} + + // Valid: partial forward — case fixed by this patch + SpecialPerson(SpecialPerson&& sp, int) + : Person(std::forward<Person>(sp)), surname(std::move(sp.surname)) {} + + // Invalid: access base class member after base move + SpecialPerson(SpecialPerson&& sp, char) + : Person(std::move(sp)), surname(std::move(sp.name)) + // CHECK-NOTES: [[@LINE-1]]:48: warning: 'sp' used after it was moved [bugprone-use-after-move] + // CHECK-NOTES: [[@LINE-2]]:7: note: move occurred here + {} +}; + +void invalidFullMove(SpecialPerson&& sp) { + SpecialPerson other(std::move(sp)); + sp.surname = "1"; + // CHECK-NOTES: [[@LINE-1]]:3: warning: 'sp' used after it was moved [bugprone-use-after-move] + // CHECK-NOTES: [[@LINE-3]]:17: note: move occurred here +} + +void invalidFullForward(SpecialPerson&& sp) { + SpecialPerson other(std::forward<SpecialPerson>(sp)); + sp.surname = "1"; + // CHECK-NOTES: [[@LINE-1]]:3: warning: 'sp' used after it was forwarded [bugprone-use-after-move] + // CHECK-NOTES: [[@LINE-3]]:17: note: forward occurred here +} +} // namespace GH63202 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
