Author: Aditya Singh Date: 2026-03-07T22:04:58+08:00 New Revision: 818168ebca24640f8cfc495abc79f658e43c7e2c
URL: https://github.com/llvm/llvm-project/commit/818168ebca24640f8cfc495abc79f658e43c7e2c DIFF: https://github.com/llvm/llvm-project/commit/818168ebca24640f8cfc495abc79f658e43c7e2c.diff LOG: [clang-tidy] Fix false positive for constrained template parameters in `cppcoreguidelines-missing-std-forward` (#182038) Explicit object parameters with a type constraint are skipped to avoid false positives. They are technically still forwarding references per [temp.deduct.call], but rarely intended to be perfectly forwarded. Fixes #180362 Added: clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward-cxx23.cpp Modified: clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp clang-tools-extra/docs/ReleaseNotes.rst clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst Removed: ################################################################################ diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp index d1d81d510c8fb..3fda2a671eaf4 100644 --- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp +++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp @@ -46,6 +46,16 @@ AST_MATCHER(ParmVarDecl, isTemplateTypeParameter) { const QualType ParamType = Node.getType().getNonPackExpansionType()->getPointeeType(); + + // Explicit object parameters with a type constraint are still forwarding + // references per [temp.deduct.call]. We conservatively suppress warnings + // here to avoid false positives when constraints restrict the deduced type, + // accepting false negatives as a trade-off. + if (Node.isExplicitObjectParameter()) + if (const auto *TTPT = ParamType->getAs<TemplateTypeParmType>()) + if (const auto *Decl = TTPT->getDecl(); Decl && Decl->hasTypeConstraint()) + return false; + const auto *TemplateType = ParamType->getAsCanonical<TemplateTypeParmType>(); if (!TemplateType) return false; diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst index b0b4cd646c3bd..9f4d7e6923fa0 100644 --- a/clang-tools-extra/docs/ReleaseNotes.rst +++ b/clang-tools-extra/docs/ReleaseNotes.rst @@ -216,6 +216,10 @@ Changes in existing checks <clang-tidy/checks/cppcoreguidelines/init-variables>` check by ensuring that member pointers are correctly flagged as uninitialized. +- Improved :doc:`cppcoreguidelines-missing-std-forward + <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by fixing + a false positive for constrained template parameters. + - Improved :doc:`cppcoreguidelines-pro-type-vararg <clang-tidy/checks/cppcoreguidelines/pro-type-vararg>` check by no longer warning on builtins with custom type checking (e.g., type-generic builtins diff --git a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst index c2af1239a7d4c..c8c0206a4d67c 100644 --- a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst +++ b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/missing-std-forward.rst @@ -45,3 +45,10 @@ Options This check implements `F.19 <http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#rf-forward>`_ from the C++ Core Guidelines. + +Limitations +----------- + +Explicit object parameters (``this Self&&``) with a type constraint are not +checked to avoid false positives. Such parameters are rarely intended to be +perfectly forwarded. diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward-cxx23.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward-cxx23.cpp new file mode 100644 index 0000000000000..723b7893673a1 --- /dev/null +++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward-cxx23.cpp @@ -0,0 +1,58 @@ +// RUN: %check_clang_tidy -std=c++23-or-later %s cppcoreguidelines-missing-std-forward %t -- -- -fno-delayed-template-parsing + +// NOLINTBEGIN +namespace std { + +template <typename T> struct remove_reference { using type = T; }; +template <typename T> struct remove_reference<T&> { using type = T; }; +template <typename T> struct remove_reference<T&&> { using type = T; }; + +template <typename T> using remove_reference_t = typename remove_reference<T>::type; + +template <typename T> constexpr T &&forward(remove_reference_t<T> &t) noexcept; +template <typename T> constexpr T &&forward(remove_reference_t<T> &&t) noexcept; +template <typename T> constexpr remove_reference_t<T> &&move(T &&x); + +template <class T, class U> +concept derived_from = true; + +template <class T> +concept integral = true; + +} // namespace std +// NOLINTEND + +// Tests for constrained explicit object parameters (GH#180362). + +// Constrained explicit object parameter is not a forwarding reference. +class GH180362_A { +public: + template <std::derived_from<GH180362_A> Self> + auto operator|(this Self &&self, int) -> void {} +}; + +// Another constrained explicit object parameter — no warning. +struct GH180362_C { + template <std::integral Self> + void bar(this Self &&self) {} +}; + +// Unconstrained explicit object parameter IS a forwarding reference. +struct GH180362_B { + template <typename Self> + void foo(this Self &&self) {} + // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: forwarding reference parameter 'self' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward] +}; + +// Requires-clause on explicit object parameter is NOT a type constraint. +struct GH180362_D { + template <typename Self> + requires std::derived_from<Self, GH180362_D> + void baz(this Self &&self) {} + // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: forwarding reference parameter 'self' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward] +}; + +// Constrained non-explicit-object parameter IS still a forwarding reference. +template <std::integral T> +void gh180362_takes_integral(T &&t) {} +// CHECK-MESSAGES: :[[@LINE-1]]:34: warning: forwarding reference parameter 't' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward] _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
