https://github.com/Aditya26189 updated https://github.com/llvm/llvm-project/pull/182038
>From f75cb44c10813ea173aae396a6ad017e1ff29fec Mon Sep 17 00:00:00 2001 From: Aditya Singh <[email protected]> Date: Wed, 18 Feb 2026 20:24:20 +0530 Subject: [PATCH] [clang-tidy][cppcoreguidelines-missing-std-forward] Fix false positive for constrained template parameters A type-constrained parameter (e.g., `std::derived_from<A> Self`) is not a forwarding reference. Check `hasTypeConstraint()` before treating `T&&` as one. Fixes #180362 --- .../MissingStdForwardCheck.cpp | 8 +++ clang-tools-extra/docs/ReleaseNotes.rst | 4 ++ .../missing-std-forward-cxx23.cpp | 58 +++++++++++++++++++ 3 files changed, 70 insertions(+) create mode 100644 clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward-cxx23.cpp diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp index d1d81d510c8fb..28240c2675205 100644 --- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp +++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp @@ -46,6 +46,14 @@ AST_MATCHER(ParmVarDecl, isTemplateTypeParameter) { const QualType ParamType = Node.getType().getNonPackExpansionType()->getPointeeType(); + + // Explicit object parameters with a type constraint are not forwarding + // references. + 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 ee057d9bf0444..5fcf1c2788af8 100644 --- a/clang-tools-extra/docs/ReleaseNotes.rst +++ b/clang-tools-extra/docs/ReleaseNotes.rst @@ -182,6 +182,10 @@ 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/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..ab5911b27a867 --- /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]]:34: 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]]:34: 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] \ No newline at end of file _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
