[clang] [clang] Implement CTAD for type alias template. (PR #77890)
via cfe-commits
cfe-commits at lists.llvm.org
Wed Mar 6 01:18:06 PST 2024
================
@@ -2612,44 +2669,312 @@ struct ConvertConstructorToDeductionGuideTransform {
SemaRef.CurrentInstantiationScope->InstantiatedLocal(OldParam, NewParam);
return NewParam;
}
+};
- FunctionTemplateDecl *buildDeductionGuide(
- TemplateParameterList *TemplateParams, CXXConstructorDecl *Ctor,
- ExplicitSpecifier ES, TypeSourceInfo *TInfo, SourceLocation LocStart,
- SourceLocation Loc, SourceLocation LocEnd,
- llvm::ArrayRef<TypedefNameDecl *> MaterializedTypedefs = {}) {
- DeclarationNameInfo Name(DeductionGuideName, Loc);
- ArrayRef<ParmVarDecl *> Params =
- TInfo->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams();
+// Find all template parameters that appear in the given DeducedArgs.
+// Return the indices of the template parameters in the TemplateParams.
+SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
+ ArrayRef<NamedDecl *> TemplateParams,
+ ArrayRef<TemplateArgument> DeducedArgs) {
+ struct FindAppearedTemplateParams
+ : public RecursiveASTVisitor<FindAppearedTemplateParams> {
+ llvm::DenseSet<NamedDecl *> TemplateParams;
+ llvm::DenseSet<const NamedDecl *> AppearedTemplateParams;
+
+ FindAppearedTemplateParams(ArrayRef<NamedDecl *> TemplateParams)
+ : TemplateParams(TemplateParams.begin(), TemplateParams.end()) {}
+
+ bool VisitTemplateTypeParmType(TemplateTypeParmType *TTP) {
+ TTP->getIndex();
+ MarkAppeared(TTP->getDecl());
+ return true;
+ }
+ bool VisitDeclRefExpr(DeclRefExpr *DRE) {
+ MarkAppeared(DRE->getFoundDecl());
+ return true;
+ }
- // Build the implicit deduction guide template.
- auto *Guide =
- CXXDeductionGuideDecl::Create(SemaRef.Context, DC, LocStart, ES, Name,
- TInfo->getType(), TInfo, LocEnd, Ctor);
- Guide->setImplicit();
- Guide->setParams(Params);
+ void MarkAppeared(NamedDecl *ND) {
+ if (TemplateParams.contains(ND))
+ AppearedTemplateParams.insert(ND);
+ }
+ };
+ FindAppearedTemplateParams MarkAppeared(TemplateParams);
+ MarkAppeared.TraverseTemplateArguments(DeducedArgs);
- for (auto *Param : Params)
- Param->setDeclContext(Guide);
- for (auto *TD : MaterializedTypedefs)
- TD->setDeclContext(Guide);
+ SmallVector<unsigned> Results;
+ for (unsigned Index = 0; Index < TemplateParams.size(); ++Index) {
+ if (MarkAppeared.AppearedTemplateParams.contains(
+ TemplateParams[Index]))
+ Results.push_back(Index);
+ }
+ return Results;
+}
+
+bool hasDeclaredDeductionGuides(DeclarationName Name, DeclContext *DC) {
+ // Check whether we've already declared deduction guides for this template.
+ // FIXME: Consider storing a flag on the template to indicate this.
+ assert(Name.getNameKind() ==
+ DeclarationName::NameKind::CXXDeductionGuideName &&
+ "name must be a deduction guide name");
+ auto Existing = DC->lookup(Name);
+ for (auto *D : Existing)
+ if (D->isImplicit())
+ return true;
+ return false;
+}
+
+// Build deduction guides for a type alias template.
+void DeclareImplicitDeductionGuidesForTypeAlias(
+ Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate, SourceLocation Loc) {
+ auto &Context = SemaRef.Context;
+ // FIXME: if there is an explicit deduction guide after the first use of the
+ // type alias usage, we will not cover this explicit deduction guide. fix this
+ // case.
+ if (hasDeclaredDeductionGuides(
+ Context.DeclarationNames.getCXXDeductionGuideName(AliasTemplate),
+ AliasTemplate->getDeclContext()))
+ return;
+ // Unwrap the sugared ElaboratedType.
+ auto RhsType = AliasTemplate->getTemplatedDecl()
+ ->getUnderlyingType()
+ .getSingleStepDesugaredType(Context);
+ TemplateDecl *Template = nullptr;
+ llvm::ArrayRef<TemplateArgument> AliasRhsTemplateArgs;
+ if (const auto *TST = RhsType->getAs<TemplateSpecializationType>()) {
+ // Cases where the RHS of the alias is dependent. e.g.
+ // template<typename T>
+ // using AliasFoo1 = Foo<T>; // a class/type alias template specialization
+ Template = TST->getTemplateName().getAsTemplateDecl();
+ AliasRhsTemplateArgs = TST->template_arguments();
+ } else if (const auto *RT = RhsType->getAs<RecordType>()) {
+ // Cases where template arguments in the RHS of the alias are not
+ // dependent. e.g.
+ // using AliasFoo = Foo<bool>;
+ if (const auto *CTSD = llvm::dyn_cast<ClassTemplateSpecializationDecl>(
+ RT->getAsCXXRecordDecl())) {
+ Template = CTSD->getSpecializedTemplate();
+ AliasRhsTemplateArgs = CTSD->getTemplateArgs().asArray();
+ }
+ } else {
+ assert(false && "unhandled RHS type of the alias");
+ }
+ if (!Template)
+ return;
+ DeclarationNameInfo NameInfo(
+ Context.DeclarationNames.getCXXDeductionGuideName(Template), Loc);
+ LookupResult Guides(SemaRef, NameInfo, clang::Sema::LookupOrdinaryName);
+ SemaRef.LookupQualifiedName(Guides, Template->getDeclContext());
+ Guides.suppressDiagnostics();
+
+ for (auto *G : Guides) {
+ FunctionTemplateDecl *F = dyn_cast<FunctionTemplateDecl>(G);
+ if (!F)
+ continue;
+ auto RType = F->getTemplatedDecl()->getReturnType();
+ // The (trailing) return type of the deduction guide.
+ const TemplateSpecializationType *FReturnType =
+ RType->getAs<TemplateSpecializationType>();
+ if (const auto *InjectedCNT = RType->getAs<InjectedClassNameType>())
+ // implicitly-generated deduction guide.
+ FReturnType = InjectedCNT->getInjectedTST();
+ else if (const auto *ET = RType->getAs<ElaboratedType>())
+ // explicit deduction guide.
+ FReturnType = ET->getNamedType()->getAs<TemplateSpecializationType>();
+ assert(FReturnType && "expected to see a return type");
+ // Deduce template arguments of the deduction guide f from the RHS of
+ // the alias.
+ //
+ // C++ [over.match.class.deduct]p3: ...For each function or function
+ // template f in the guides of the template named by the
+ // simple-template-id of the defining-type-id, the template arguments
+ // of the return type of f are deduced from the defining-type-id of A
+ // according to the process in [temp.deduct.type] with the exception
+ // that deduction does not fail if not all template arguments are
+ // deduced.
+ //
+ //
+ // template<typename X, typename Y>
+ // f(X, Y) -> f<Y, X>;
+ //
+ // template<typename U>
+ // using alias = f<int, U>;
+ //
+ // The RHS of alias is f<int, U>, we deduced the template arguments of
+ // the return type of the deduction guide from it: Y->int, X->U
+ sema::TemplateDeductionInfo TDeduceInfo(Loc);
+ // Must initialize n elements, this is required by DeduceTemplateArguments.
+ SmallVector<DeducedTemplateArgument> DeduceResults(
+ F->getTemplateParameters()->size());
+
+ // FIXME: DeduceTemplateArguments stops immediately at the first
+ // non-deducible template argument. However, this doesn't seem to casue
+ // issues for practice cases, we probably need to extend it to continue
+ // performing deduction for rest of arguments to align with the C++
+ // standard.
+ SemaRef.DeduceTemplateArguments(
+ F->getTemplateParameters(), FReturnType->template_arguments(),
+ AliasRhsTemplateArgs, TDeduceInfo, DeduceResults,
+ /*NumberOfArgumentsMustMatch=*/false);
+
+ SmallVector<TemplateArgument> DeducedArgs;
+ SmallVector<unsigned> NonDeducedTemplateParamsInFIndex;
+ // !!NOTE: DeduceResults respects the sequence of template parameters of
+ // the deduction guide f.
+ for (unsigned Index = 0; Index < DeduceResults.size(); ++Index) {
+ if (const auto &D = DeduceResults[Index]; !D.isNull()) // Deduced
+ DeducedArgs.push_back(D);
+ else
+ NonDeducedTemplateParamsInFIndex.push_back(Index);
+ }
+ auto DeducedAliasTemplateParams =
+ TemplateParamsReferencedInTemplateArgumentList(
+ AliasTemplate->getTemplateParameters()->asArray(), DeducedArgs);
+ // All template arguments null by default.
+ SmallVector<TemplateArgument> TemplateArgsForBuildingFPrime(
+ F->getTemplateParameters()->size());
+
+ Sema::InstantiatingTemplate BuildingDeductionGuides(
+ SemaRef, AliasTemplate->getLocation(), F,
+ Sema::InstantiatingTemplate::BuildingDeductionGuidesTag{});
+ if (BuildingDeductionGuides.isInvalid())
+ return;
+ LocalInstantiationScope Scope(SemaRef);
- auto *GuideTemplate = FunctionTemplateDecl::Create(
- SemaRef.Context, DC, Loc, DeductionGuideName, TemplateParams, Guide);
- GuideTemplate->setImplicit();
- Guide->setDescribedFunctionTemplate(GuideTemplate);
+ // Create a template parameter list for the synthesized deduction guide f'.
+ //
+ // C++ [over.match.class.deduct]p3.2:
+ // If f is a function template, f' is a function template whose template
+ // parameter list consists of all the template parameters of A
+ // (including their default template arguments) that appear in the above
+ // deductions or (recursively) in their default template arguments
+ SmallVector<NamedDecl *> FPrimeTemplateParams;
+ // Store template arguments that refer to the newly-created template
+ // parameters, used for building `TemplateArgsForBuildingFPrime`.
+ SmallVector<TemplateArgument, 16> TransformedDeducedAliasArgs(
+ AliasTemplate->getTemplateParameters()->size());
+ auto TransformTemplateParameter =
+ [&SemaRef](DeclContext *DC, NamedDecl *TemplateParam,
+ MultiLevelTemplateArgumentList &Args,
+ unsigned NewIndex) -> NamedDecl * {
+ if (auto *TTP = dyn_cast<TemplateTypeParmDecl>(TemplateParam))
+ return transformTemplateTypeParam(SemaRef, DC, TTP, Args,
+ TTP->getDepth(), NewIndex);
+ if (auto *TTP = dyn_cast<TemplateTemplateParmDecl>(TemplateParam))
+ return transformTemplateParam(SemaRef, DC, TTP, Args, NewIndex,
+ TTP->getDepth());
+ if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(TemplateParam))
+ return transformTemplateParam(SemaRef, DC, NTTP, Args, NewIndex,
+ NTTP->getDepth());
+ return nullptr;
+ };
- if (isa<CXXRecordDecl>(DC)) {
- Guide->setAccess(AS_public);
- GuideTemplate->setAccess(AS_public);
+ for (unsigned AliasTemplateParamIdx : DeducedAliasTemplateParams) {
+ auto *TP = AliasTemplate->getTemplateParameters()->getParam(
+ AliasTemplateParamIdx);
+ // Rebuild any internal references to earlier parameters and reindex as
+ // we go.
+ MultiLevelTemplateArgumentList Args;
+ Args.setKind(TemplateSubstitutionKind::Rewrite);
+ Args.addOuterTemplateArguments(TransformedDeducedAliasArgs);
+ NamedDecl *NewParam =
+ TransformTemplateParameter(AliasTemplate->getDeclContext(), TP, Args,
+ /*NewIndex*/ FPrimeTemplateParams.size());
+ FPrimeTemplateParams.push_back(NewParam);
+
+ auto NewTemplateArgument = Context.getCanonicalTemplateArgument(
+ Context.getInjectedTemplateArg(NewParam));
+ TransformedDeducedAliasArgs[AliasTemplateParamIdx] = NewTemplateArgument;
+ }
+ // ...followed by the template parameters of f that were not deduced
+ // (including their default template arguments)
+ for (unsigned FTemplateParamIdx : NonDeducedTemplateParamsInFIndex) {
+ auto *TP = F->getTemplateParameters()->getParam(FTemplateParamIdx);
+ MultiLevelTemplateArgumentList Args;
+ Args.setKind(TemplateSubstitutionKind::Rewrite);
+ // We take a shortcut here, it is ok to reuse the
+ // TemplateArgsForBuildingFPrime.
+ Args.addOuterTemplateArguments(TemplateArgsForBuildingFPrime);
+ NamedDecl *NewParam = TransformTemplateParameter(
+ F->getDeclContext(), TP, Args, FPrimeTemplateParams.size());
+ FPrimeTemplateParams.push_back(NewParam);
+
+ assert(TemplateArgsForBuildingFPrime[FTemplateParamIdx].isNull() &&
+ "The argument must be null before setting");
+ TemplateArgsForBuildingFPrime[FTemplateParamIdx] =
+ Context.getCanonicalTemplateArgument(
+ Context.getInjectedTemplateArg(NewParam));
+ }
+ // FIXME: support require clause.
----------------
cor3ntin wrote:
So this is missing https://eel.is/c++draft/over.match.class.deduct#3.3
I think we need to create a Binary (and) op expression with the requires clause of F and, a literal bool expression set to whether the arguments are deducible (do we implement the deducible part?)
https://github.com/llvm/llvm-project/pull/77890
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