Author: Utkarsh Saxena Date: 2023-10-20T14:40:25+02:00 New Revision: 47747da6340b00e301d3656f95ecf9b04a6ec2bb
URL: https://github.com/llvm/llvm-project/commit/47747da6340b00e301d3656f95ecf9b04a6ec2bb DIFF: https://github.com/llvm/llvm-project/commit/47747da6340b00e301d3656f95ecf9b04a6ec2bb.diff LOG: [clang] Handle templated operators with reversed arguments (#69595) https://github.com/llvm/llvm-project/pull/68999 correctly computed conversion sequence for reversed args to a template operators. This was a breaking change as code, previously accepted in C++17, starts to break in C++20. Example: ```cpp struct P {}; template<class S> bool operator==(const P&, const S &); struct A : public P {}; struct B : public P {}; bool check(A a, B b) { return a == b; } // This is now ambiguous in C++20. ``` In order to minimise widespread breakages, as a clang extension, we had previously accepted such ambiguities with a warning (`-Wambiguous-reversed-operator`) for non-template operators. Due to the same reasons, we extend this relaxation for template operators. Fixes https://github.com/llvm/llvm-project/issues/53954 Added: Modified: clang/docs/ReleaseNotes.rst clang/lib/Sema/SemaOverload.cpp clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp Removed: ################################################################################ diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index fc8caf9221b9d29..848f3559d06ff8a 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -37,6 +37,27 @@ These changes are ones which we think may surprise users when upgrading to Clang |release| because of the opportunity they pose for disruption to existing code bases. +- Fix a bug in reversed argument for templated operators. + This breaks code in C++20 which was previously accepted in C++17. Eg: + + .. code-block:: cpp + + struct P {}; + template<class S> bool operator==(const P&, const S&); + + struct A : public P {}; + struct B : public P {}; + + // This equality is now ambiguous in C++20. + bool ambiguous(A a, B b) { return a == b; } + + template<class S> bool operator!=(const P&, const S&); + // Ok. Found a matching operator!=. + bool fine(A a, B b) { return a == b; } + + To reduce such widespread breakages, as an extension, Clang accepts this code + with an existing warning ``-Wambiguous-reversed-operator`` warning. + Fixes `GH <https://github.com/llvm/llvm-project/issues/53954>`_. C/C++ Language Potentially Breaking Changes ------------------------------------------- diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp index ce78994e6553814..d57a7ad8f46859a 100644 --- a/clang/lib/Sema/SemaOverload.cpp +++ b/clang/lib/Sema/SemaOverload.cpp @@ -7688,7 +7688,7 @@ bool Sema::CheckNonDependentConversions( QualType ParamType = ParamTypes[I + Offset]; if (!ParamType->isDependentType()) { unsigned ConvIdx = PO == OverloadCandidateParamOrder::Reversed - ? 0 + ? Args.size() - 1 - (ThisConversions + I) : (ThisConversions + I); Conversions[ConvIdx] = TryCopyInitialization(*this, Args[I], ParamType, @@ -10085,11 +10085,19 @@ getImplicitObjectParamType(ASTContext &Context, const FunctionDecl *F) { return M->getFunctionObjectParameterReferenceType(); } -static bool haveSameParameterTypes(ASTContext &Context, const FunctionDecl *F1, - const FunctionDecl *F2) { +// As a Clang extension, allow ambiguity among F1 and F2 if they represent +// represent the same entity. +static bool allowAmbiguity(ASTContext &Context, const FunctionDecl *F1, + const FunctionDecl *F2) { if (declaresSameEntity(F1, F2)) return true; - + if (F1->isTemplateInstantiation() && F2->isTemplateInstantiation() && + declaresSameEntity(F1->getPrimaryTemplate(), F2->getPrimaryTemplate())) { + return true; + } + // TODO: It is not clear whether comparing parameters is necessary (i.e. + // diff erent functions with same params). Consider removing this (as no test + // fail w/o it). auto NextParam = [&](const FunctionDecl *F, unsigned &I, bool First) { if (First) { if (std::optional<QualType> T = getImplicitObjectParamType(Context, F)) @@ -10274,14 +10282,14 @@ bool clang::isBetterOverloadCandidate( case ImplicitConversionSequence::Worse: if (Cand1.Function && Cand2.Function && Cand1.isReversed() != Cand2.isReversed() && - haveSameParameterTypes(S.Context, Cand1.Function, Cand2.Function)) { + allowAmbiguity(S.Context, Cand1.Function, Cand2.Function)) { // Work around large-scale breakage caused by considering reversed // forms of operator== in C++20: // - // When comparing a function against a reversed function with the same - // parameter types, if we have a better conversion for one argument and - // a worse conversion for the other, the implicit conversion sequences - // are treated as being equally good. + // When comparing a function against a reversed function, if we have a + // better conversion for one argument and a worse conversion for the + // other, the implicit conversion sequences are treated as being equally + // good. // // This prevents a comparison function from being considered ambiguous // with a reversed form that is written in the same way. @@ -14421,7 +14429,7 @@ ExprResult Sema::CreateOverloadedBinOp(SourceLocation OpLoc, llvm::SmallVector<FunctionDecl*, 4> AmbiguousWith; for (OverloadCandidate &Cand : CandidateSet) { if (Cand.Viable && Cand.Function && Cand.isReversed() && - haveSameParameterTypes(Context, Cand.Function, FnDecl)) { + allowAmbiguity(Context, Cand.Function, FnDecl)) { for (unsigned ArgIdx = 0; ArgIdx < 2; ++ArgIdx) { if (CompareImplicitConversionSequences( *this, OpLoc, Cand.Conversions[ArgIdx], diff --git a/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp b/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp index 5c6804eb7726b5f..5727d506fe5e61d 100644 --- a/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp +++ b/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp @@ -324,6 +324,67 @@ bool x = X() == X(); // expected-warning {{ambiguous}} } } // namespace P2468R2 +namespace GH53954{ +namespace friend_template_1 { +struct P { + template <class T> + friend bool operator==(const P&, const T&); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} +}; +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + +namespace friend_template_2 { +struct P { + template <class T> + friend bool operator==(const T&, const P&); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} +}; +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + +namespace member_template { +struct P { + template<class S> + bool operator==(const S &) const; // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} +}; +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + +namespace non_member_template_1 { +struct P {}; +template<class S> +bool operator==(const P&, const S &); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} + +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} + +template<class S> +bool operator!=(const P&, const S &); +bool fine(A a, B b) { return a == b; } // Ok. Found a matching operator!=. +} +} + +namespace non_member_template_2 { +struct P {}; +template<class S> +bool operator==(const S&, const P&); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} + +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + #else // NO_ERRORS namespace problem_cases { _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
