Author: Oleksandr T. Date: 2024-11-27T11:51:34+02:00 New Revision: eb001820b47176fc3e7bc643525c6352b76dcd1d
URL: https://github.com/llvm/llvm-project/commit/eb001820b47176fc3e7bc643525c6352b76dcd1d DIFF: https://github.com/llvm/llvm-project/commit/eb001820b47176fc3e7bc643525c6352b76dcd1d.diff LOG: [Clang] prevent errors for deduction guides using deduced type aliases (#117450) Fixes #54909 --- Clang incorrectly produces diagnostics for alias templates in deduction guides, treating them as separate from their underlying types. This issue arises because Clang doesn't properly handle `TypeAliasTemplateDecl` when comparing template names for equality in the context of deduction guides, resulting in diagnostics that don't align with the C++ standard. As the C++ standard specifies - _an alias template is considered a synonym for its underlying type_ With this change, Clang now correctly resolves alias templates to their underlying types in deduction guides, ensuring compliance with the C++ standard. Added: Modified: clang/docs/ReleaseNotes.rst clang/lib/Sema/SemaDeclCXX.cpp clang/test/CXX/temp/temp.deduct.guide/p3.cpp Removed: ################################################################################ diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 6c40e48e2f49b3..356b091c13af4f 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -590,6 +590,9 @@ Improvements to Clang's diagnostics - Fixed a false negative ``-Wunused-private-field`` diagnostic when a defaulted comparison operator is defined out of class (#GH116961). +- Clang now supports using alias templates in deduction guides, aligning with the C++ standard, + which treats alias templates as synonyms for their underlying types (#GH54909). + Improvements to Clang's time-trace ---------------------------------- diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp index 26041e53de5061..3ff365649c93d2 100644 --- a/clang/lib/Sema/SemaDeclCXX.cpp +++ b/clang/lib/Sema/SemaDeclCXX.cpp @@ -11451,23 +11451,29 @@ bool Sema::CheckDeductionGuideDeclarator(Declarator &D, QualType &R, bool MightInstantiateToSpecialization = false; if (auto RetTST = TSI->getTypeLoc().getAsAdjusted<TemplateSpecializationTypeLoc>()) { - TemplateName SpecifiedName = RetTST.getTypePtr()->getTemplateName(); - bool TemplateMatches = Context.hasSameTemplateName( - SpecifiedName, GuidedTemplate, /*IgnoreDeduced=*/true); - - const QualifiedTemplateName *Qualifiers = - SpecifiedName.getAsQualifiedTemplateName(); - assert(Qualifiers && "expected QualifiedTemplate"); - bool SimplyWritten = !Qualifiers->hasTemplateKeyword() && - Qualifiers->getQualifier() == nullptr; - if (SimplyWritten && TemplateMatches) - AcceptableReturnType = true; - else { - // This could still instantiate to the right type, unless we know it - // names the wrong class template. - auto *TD = SpecifiedName.getAsTemplateDecl(); - MightInstantiateToSpecialization = !(TD && isa<ClassTemplateDecl>(TD) && - !TemplateMatches); + const TemplateSpecializationType *TST = RetTST.getTypePtr(); + while (TST && TST->isTypeAlias()) + TST = TST->getAliasedType()->getAs<TemplateSpecializationType>(); + + if (TST) { + TemplateName SpecifiedName = TST->getTemplateName(); + bool TemplateMatches = Context.hasSameTemplateName( + SpecifiedName, GuidedTemplate, /*IgnoreDeduced=*/true); + + const QualifiedTemplateName *Qualifiers = + SpecifiedName.getAsQualifiedTemplateName(); + assert(Qualifiers && "expected QualifiedTemplate"); + bool SimplyWritten = !Qualifiers->hasTemplateKeyword() && + Qualifiers->getQualifier() == nullptr; + if (SimplyWritten && TemplateMatches) + AcceptableReturnType = true; + else { + // This could still instantiate to the right type, unless we know it + // names the wrong class template. + auto *TD = SpecifiedName.getAsTemplateDecl(); + MightInstantiateToSpecialization = + !(TD && isa<ClassTemplateDecl>(TD) && !TemplateMatches); + } } } else if (!RetTy.hasQualifiers() && RetTy->isDependentType()) { MightInstantiateToSpecialization = true; diff --git a/clang/test/CXX/temp/temp.deduct.guide/p3.cpp b/clang/test/CXX/temp/temp.deduct.guide/p3.cpp index c5404847beb066..195ba2831439d0 100644 --- a/clang/test/CXX/temp/temp.deduct.guide/p3.cpp +++ b/clang/test/CXX/temp/temp.deduct.guide/p3.cpp @@ -33,7 +33,7 @@ template<template<typename> typename TT> struct E { // expected-note 2{{template }; A(int) -> int; // expected-error {{deduced type 'int' of deduction guide is not a specialization of template 'A'}} -template <typename T> A(T)->B<T>; // expected-error {{deduced type 'B<T>' (aka 'A<T>') of deduction guide is not written as a specialization of template 'A'}} +template <typename T> A(T)->B<T>; template<typename T> A(T*) -> const A<T>; // expected-error {{deduced type 'const A<T>' of deduction guide is not a specialization of template 'A'}} // A deduction-guide shall be declared in the same scope as the corresponding @@ -71,3 +71,11 @@ namespace WrongScope { Local(int) -> Local<int>; // expected-error {{expected}} } } + +namespace GH54909 { +template <class T> struct A {}; +struct B {}; + +template <typename T> using C = B; +template <typename T> A() -> C<T>; // expected-error {{deduced type 'C<T>' (aka 'GH54909::B') of deduction guide is not a specialization of template 'A'}} +} _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
