https://github.com/cor3ntin created https://github.com/llvm/llvm-project/pull/224291
We did not implement the CWG200 changes to [dcl.type.auto.deduct] The rest seems to be working - I added tests, both for this issue and all examplars in the wording. (i.e, deducing `auto` from `a decltype(auto) template parameter is rejected) I thought it was cleaner to reuse getNTTParameterFromExpr rather than duplicating it, so there is a bunch of churn there to rename it. Note that GCC doesn't seem to fully support that resolution ( To say nothing of other implementations). Assisted-By: Opus 5. >From 7f9adf41e5998c32c58d19a0da6e3cee29b672ec Mon Sep 17 00:00:00 2001 From: Corentin Jabot <[email protected]> Date: Tue, 15 Sep 2026 20:53:10 +0200 Subject: [PATCH] [Clang] Implement CWG2900 We did not implement the CWG200 changes to [dcl.type.auto.deduct] The rest seems to be working - I added tests, both for this issue and all examplars in the wording. (i.e, deducing `auto` from `a decltype(auto) template parameter is rejected) I thought it was cleaner to reuse getNTTParameterFromExpr rather than duplicating it, so there is a bunch of churn there to rename it. Note that GCC doesn;t seem to fully support that resolution ( To say nothing of other implementations). Assisted-By: Opus 5. --- clang/docs/ReleaseNotes.md | 4 ++ clang/include/clang/Sema/Sema.h | 6 ++ clang/lib/Sema/SemaTemplate.cpp | 16 +++++ clang/lib/Sema/SemaTemplateDeduction.cpp | 53 +++++++++------- clang/test/CXX/drs/cwg29xx.cpp | 32 ++++++++++ .../temp_arg_nontype_arg_type.cpp | 63 +++++++++++++++++++ clang/www/cxx_dr_status.html | 2 +- 7 files changed, 152 insertions(+), 24 deletions(-) create mode 100644 clang/test/SemaTemplate/temp_arg_nontype_arg_type.cpp diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md index 0d67179f91a49..bd4398e632340 100644 --- a/clang/docs/ReleaseNotes.md +++ b/clang/docs/ReleaseNotes.md @@ -194,6 +194,10 @@ features cannot lower the translation-unit ABI level; them to an enumeration type with a fixed `bool` underlying type. This resolves [CWG1094](https://wg21.link/cwg1094). +- Implemented [CWG2900](https://wg21.link/cwg2900), removing an ambiguity + when partial ordering constant template parameters declared + with placeholder types. + ### C Language Changes #### C2y Feature Support diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h index 0864337a9374c..b91e82680edc0 100644 --- a/clang/include/clang/Sema/Sema.h +++ b/clang/include/clang/Sema/Sema.h @@ -12955,6 +12955,12 @@ class Sema final : public SemaBase { const DefaultArguments &DefaultArgs, SourceLocation ArgLoc, bool PartialOrdering, bool *StrictPackMatch); + /// Determine the declared type of the constant template parameter that \p A + /// names, if any. + static QualType + getTypeOfConstantTemplateParameter(const TemplateArgument &A, + UnsignedOrNone Depth = std::nullopt); + /// Mark which template parameters are used in a given expression. /// /// \param E the expression from which template parameters will be deduced. diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp index 50ff56ff7811e..2288cd7441f03 100644 --- a/clang/lib/Sema/SemaTemplate.cpp +++ b/clang/lib/Sema/SemaTemplate.cpp @@ -5566,6 +5566,22 @@ bool Sema::CheckTemplateArgument(NamedDecl *Param, TemplateArgumentLoc &ArgLoc, if (NTTP->isParameterPack() && NTTP->isExpandedParameterPack()) NTTPType = NTTP->getExpansionType(ArgumentPackIndex); + // C++26 [dcl.type.auto.deduct]p3: + // If the placeholder-type-specifier is of the form type-constraint_opt + // auto, [...] If E is a value synthesized for a constant template + // parameter of type decltype(auto) ([temp.func.order]), the declaration + // is ill-formed. + auto isUndeducedAuto = [](QualType T, bool DecltypeAuto) { + const AutoType *AT = T->getContainedAutoType(); + return AT && AT->isDecltypeAuto() == DecltypeAuto && + AT->getDeducedType().isNull(); + }; + if (CTAI.PartialOrdering && + isUndeducedAuto(NTTPType, /*DecltypeAuto=*/false) && + isUndeducedAuto(getTypeOfConstantTemplateParameter(Arg), + /*DecltypeAuto=*/true)) + return true; + if (NTTPType->isInstantiationDependentType()) { // Do substitution on the type of the non-type template parameter. InstantiatingTemplate Inst(*this, TemplateLoc, Template, NTTP, diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp index 653240092e64a..4ba2d54e61428 100644 --- a/clang/lib/Sema/SemaTemplateDeduction.cpp +++ b/clang/lib/Sema/SemaTemplateDeduction.cpp @@ -234,31 +234,39 @@ class NonTypeOrVarTemplateParmDecl { const NamedDecl *Template; }; -/// If the given expression is of a form that permits the deduction -/// of a non-type template parameter, return the declaration of that -/// non-type template parameter. +/// If the given expression is of a form that names a non-type template +/// parameter, return the declaration of that parameter. A null \p Depth +/// accepts a parameter at any depth. static NonTypeOrVarTemplateParmDecl -getDeducedNTTParameterFromExpr(const Expr *E, unsigned Depth) { +getNTTParameterFromExpr(const Expr *E, UnsignedOrNone Depth) { // If we are within an alias template, the expression may have undergone // any number of parameter substitutions already. E = unwrapExpressionForDeduction(E); if (const auto *DRE = dyn_cast<DeclRefExpr>(E)) if (const auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(DRE->getDecl())) - if (NTTP->getDepth() == Depth) + if (!Depth || NTTP->getDepth() == *Depth) return NTTP; // A pack-index-template-name is not deducible. if (const auto *DTI = dyn_cast<DependentTemplateIdExpr>(E)) if (!DTI->getTemplateName().getAsPackIndexingTemplate() && - DTI->getParameter()->getDepth() == Depth) + (!Depth || DTI->getParameter()->getDepth() == *Depth)) return DTI->getParameter(); return nullptr; } +QualType Sema::getTypeOfConstantTemplateParameter(const TemplateArgument &A, + UnsignedOrNone Depth) { + if (NonTypeOrVarTemplateParmDecl NTTP = + getNTTParameterFromExpr(A.getAsExpr(), Depth)) + return NTTP.getType(); + return QualType(); +} + static const NonTypeOrVarTemplateParmDecl -getDeducedNTTParameterFromExpr(TemplateDeductionInfo &Info, Expr *E) { - return getDeducedNTTParameterFromExpr(E, Info.getDeducedDepth()); +getNTTParameterFromExpr(TemplateDeductionInfo &Info, Expr *E) { + return getNTTParameterFromExpr(E, Info.getDeducedDepth()); } /// Determine whether two declaration pointers refer to the same @@ -1996,7 +2004,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Determine the array bound is something we can deduce. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, DAP->getSizeExpr()); + getNTTParameterFromExpr(Info, DAP->getSizeExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2060,7 +2068,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // type. libstdc++ relies on this. Expr *NoexceptExpr = FPP->getNoexceptExpr(); if (NonTypeOrVarTemplateParmDecl NTTP = - NoexceptExpr ? getDeducedNTTParameterFromExpr(Info, NoexceptExpr) + NoexceptExpr ? getNTTParameterFromExpr(Info, NoexceptExpr) : nullptr) { assert(NTTP.getDepth() == Info.getDeducedDepth() && "saw non-type template parameter with wrong depth"); @@ -2250,7 +2258,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Perform deduction on the vector size, if we can. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, VP->getSizeExpr()); + getNTTParameterFromExpr(Info, VP->getSizeExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2276,7 +2284,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Perform deduction on the vector size, if we can. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, VP->getSizeExpr()); + getNTTParameterFromExpr(Info, VP->getSizeExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2305,7 +2313,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Perform deduction on the vector size, if we can. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, VP->getSizeExpr()); + getNTTParameterFromExpr(Info, VP->getSizeExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2330,7 +2338,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Perform deduction on the vector size, if we can. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, VP->getSizeExpr()); + getNTTParameterFromExpr(Info, VP->getSizeExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2407,7 +2415,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( } NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, ParamExpr); + getNTTParameterFromExpr(Info, ParamExpr); if (!NTTP) return TemplateDeductionResult::Success; @@ -2454,7 +2462,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Perform deduction on the address space, if we can. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, ASP->getAddrSpaceExpr()); + getNTTParameterFromExpr(Info, ASP->getAddrSpaceExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2479,7 +2487,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( // Perform deduction on the address space, if we can. NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, ASP->getAddrSpaceExpr()); + getNTTParameterFromExpr(Info, ASP->getAddrSpaceExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2499,7 +2507,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch( return TemplateDeductionResult::NonDeducedMismatch; NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, IP->getNumBitsExpr()); + getNTTParameterFromExpr(Info, IP->getNumBitsExpr()); if (!NTTP) return TemplateDeductionResult::Success; @@ -2648,7 +2656,7 @@ DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams, case TemplateArgument::Expression: if (NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(Info, P.getAsExpr())) { + getNTTParameterFromExpr(Info, P.getAsExpr())) { switch (A.getKind()) { case TemplateArgument::Expression: { return DeduceNonTypeTemplateArgument( @@ -4569,8 +4577,8 @@ static TemplateDeductionResult DeduceFromInitializerList( // from the length of the initializer list. if (auto *DependentArrTy = dyn_cast_or_null<DependentSizedArrayType>(ArrTy)) { // Determine the array bound is something we can deduce. - if (NonTypeOrVarTemplateParmDecl NTTP = getDeducedNTTParameterFromExpr( - Info, DependentArrTy->getSizeExpr())) { + if (NonTypeOrVarTemplateParmDecl NTTP = + getNTTParameterFromExpr(Info, DependentArrTy->getSizeExpr())) { // We can perform template argument deduction for the given non-type // template parameter. // C++ [temp.deduct.type]p13: @@ -6920,8 +6928,7 @@ MarkUsedTemplateParameters(ASTContext &Ctx, return; } - const NonTypeOrVarTemplateParmDecl NTTP = - getDeducedNTTParameterFromExpr(E, Depth); + const NonTypeOrVarTemplateParmDecl NTTP = getNTTParameterFromExpr(E, Depth); if (!NTTP) return; if (NTTP.getDepth() == Depth) diff --git a/clang/test/CXX/drs/cwg29xx.cpp b/clang/test/CXX/drs/cwg29xx.cpp index 165c2943b6b4a..88f57afbf7e99 100644 --- a/clang/test/CXX/drs/cwg29xx.cpp +++ b/clang/test/CXX/drs/cwg29xx.cpp @@ -8,6 +8,38 @@ // cxx98-no-diagnostics +namespace cwg2900 { // cwg2900: 24 +#if __cplusplus >= 201703L +// [temp.deduct.type] Example 13. +template <int &> struct E; +template <auto x> void f(E<x> *); // #cwg2900-f-E +int v; +void g(E<v> *bp) { + f(bp); + // since-cxx11-error@-1 {{no matching function for call to 'f'}} + // since-cxx11-note@#cwg2900-f-E {{candidate template ignored: substitution failure: non-type template argument is not a constant expression}} +} + +template <const int &> struct F; +template <decltype(auto) x> void f(F<x> *); +int i; +void g(F<i> *ap) { + f(ap); // OK, deduces x as a constant template parameter of type const int & +} + +template <decltype(auto) q> struct G; +template <auto x> long *f(G<x> *); // #1 +template <decltype(auto) x> short *f(G<x> *); // #2 +const int j = 0; +short *g(G<(j)> *ap) { // OK, q has type const int & + return f(ap); // OK, only #2 matches +} +long *g(G<j> *ap) { // OK, q has type int + return f(ap); // OK, #1 is more specialized +} +#endif +} // namespace cwg2900 + namespace cwg2913 { // cwg2913: 20 #if __cplusplus >= 202002L diff --git a/clang/test/SemaTemplate/temp_arg_nontype_arg_type.cpp b/clang/test/SemaTemplate/temp_arg_nontype_arg_type.cpp new file mode 100644 index 0000000000000..01290d91a2e84 --- /dev/null +++ b/clang/test/SemaTemplate/temp_arg_nontype_arg_type.cpp @@ -0,0 +1,63 @@ +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++14 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++17 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++2c %s + +namespace ex1 { + template<int i> class A { }; + template<short s> void f(A<s>); + // expected-note@-1 {{candidate template ignored: substitution failure: deduced non-type template argument does not have the same type as the corresponding template parameter ('int' vs 'short')}} + void k1() { + A<1> a; + f(a); // expected-error {{no matching function for call to 'f'}} + f<1>(a); + } +} + +namespace ex2 { + template<const short cs> class B { }; + template<short s> void g(B<s>); + void k2() { + B<1> b; + g(b); + } +} + +#if __cplusplus >= 201703L +namespace ex3 { + template<auto> struct C; + template<long long x> void f(C<x> *); + void g(C<0LL> *ap) { f(ap); } +} + +namespace ex4 { + template<int> struct D; + template<auto x> void f(D<x> *); + void g(D<0LL> *ap) { f(ap); } +} + +namespace ex5 { + template<int &> struct E; + template<auto x> void f(E<x> *); + // expected-note@-1 {{candidate template ignored: substitution failure: non-type template argument is not a constant expression}} + int v; + void g(E<v> *bp) { f(bp); } // expected-error {{no matching function for call to 'f'}} +} + +namespace ex6 { + template<const int &> struct F; + template<decltype(auto) x> void f(F<x> *); + int i; + void g(F<i> *ap) { f(ap); } +} + +namespace ex7 { + template <decltype(auto) q> struct G; + template <auto x> long *f(G<x> *); + template <decltype(auto) x> short *f(G<x> *); + const int j = 0; + short *g1(G<(j)> *ap) { return f(ap); } + long *g2(G<j> *ap) { return f(ap); } +} +#endif diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html index e7679da30d5c2..4970d64f754f4 100755 --- a/clang/www/cxx_dr_status.html +++ b/clang/www/cxx_dr_status.html @@ -20117,7 +20117,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2> <td>[<a href="https://wg21.link/temp.deduct.type";>temp.deduct.type</a>]</td> <td>C++26</td> <td>Deduction of non-type template arguments with placeholder types</td> - <td class="unknown" align="center">Unknown</td> + <td class="unreleased" align="center">Clang 24</td> </tr> <tr id="2901"> <td><a href="https://cplusplus.github.io/CWG/issues/2901.html";>2901</a></td> _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
