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llvm-project/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
Matheus Izvekov cfee056b4e
[clang] NFC: introduce UnsignedOrNone as a replacement for std::optional<unsigned> (#134142) 
This introduces a new class 'UnsignedOrNone', which models a lite
version of `std::optional<unsigned>`, but has the same size as
'unsigned'.

This replaces most uses of `std::optional<unsigned>`, and similar
schemes utilizing 'int' and '-1' as sentinel.

Besides the smaller size advantage, this is simpler to serialize, as its
internal representation is a single unsigned int as well.
2025-04-03 14:27:18 -03:00

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//===- SemaTemplateDeductionGude.cpp - Template Argument Deduction---------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements deduction guides for C++ class template argument
// deduction.
//
//===----------------------------------------------------------------------===//
#include "TreeTransform.h"
#include "TypeLocBuilder.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclFriend.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/TemplateName.h"
#include "clang/AST/Type.h"
#include "clang/AST/TypeLoc.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/Specifiers.h"
#include "clang/Basic/TypeTraits.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/Overload.h"
#include "clang/Sema/Ownership.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/Template.h"
#include "clang/Sema/TemplateDeduction.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <optional>
#include <utility>
using namespace clang;
using namespace sema;
namespace {
/// Tree transform to "extract" a transformed type from a class template's
/// constructor to a deduction guide.
class ExtractTypeForDeductionGuide
: public TreeTransform<ExtractTypeForDeductionGuide> {
llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs;
ClassTemplateDecl *NestedPattern;
const MultiLevelTemplateArgumentList *OuterInstantiationArgs;
std::optional<TemplateDeclInstantiator> TypedefNameInstantiator;
public:
typedef TreeTransform<ExtractTypeForDeductionGuide> Base;
ExtractTypeForDeductionGuide(
Sema &SemaRef,
llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs,
ClassTemplateDecl *NestedPattern = nullptr,
const MultiLevelTemplateArgumentList *OuterInstantiationArgs = nullptr)
: Base(SemaRef), MaterializedTypedefs(MaterializedTypedefs),
NestedPattern(NestedPattern),
OuterInstantiationArgs(OuterInstantiationArgs) {
if (OuterInstantiationArgs)
TypedefNameInstantiator.emplace(
SemaRef, SemaRef.getASTContext().getTranslationUnitDecl(),
*OuterInstantiationArgs);
}
TypeSourceInfo *transform(TypeSourceInfo *TSI) { return TransformType(TSI); }
/// Returns true if it's safe to substitute \p Typedef with
/// \p OuterInstantiationArgs.
bool mightReferToOuterTemplateParameters(TypedefNameDecl *Typedef) {
if (!NestedPattern)
return false;
static auto WalkUp = [](DeclContext *DC, DeclContext *TargetDC) {
if (DC->Equals(TargetDC))
return true;
while (DC->isRecord()) {
if (DC->Equals(TargetDC))
return true;
DC = DC->getParent();
}
return false;
};
if (WalkUp(Typedef->getDeclContext(), NestedPattern->getTemplatedDecl()))
return true;
if (WalkUp(NestedPattern->getTemplatedDecl(), Typedef->getDeclContext()))
return true;
return false;
}
QualType
RebuildTemplateSpecializationType(TemplateName Template,
SourceLocation TemplateNameLoc,
TemplateArgumentListInfo &TemplateArgs) {
if (!OuterInstantiationArgs ||
!isa_and_present<TypeAliasTemplateDecl>(Template.getAsTemplateDecl()))
return Base::RebuildTemplateSpecializationType(Template, TemplateNameLoc,
TemplateArgs);
auto *TATD = cast<TypeAliasTemplateDecl>(Template.getAsTemplateDecl());
auto *Pattern = TATD;
while (Pattern->getInstantiatedFromMemberTemplate())
Pattern = Pattern->getInstantiatedFromMemberTemplate();
if (!mightReferToOuterTemplateParameters(Pattern->getTemplatedDecl()))
return Base::RebuildTemplateSpecializationType(Template, TemplateNameLoc,
TemplateArgs);
Decl *NewD =
TypedefNameInstantiator->InstantiateTypeAliasTemplateDecl(TATD);
if (!NewD)
return QualType();
auto *NewTATD = cast<TypeAliasTemplateDecl>(NewD);
MaterializedTypedefs.push_back(NewTATD->getTemplatedDecl());
return Base::RebuildTemplateSpecializationType(
TemplateName(NewTATD), TemplateNameLoc, TemplateArgs);
}
QualType TransformTypedefType(TypeLocBuilder &TLB, TypedefTypeLoc TL) {
ASTContext &Context = SemaRef.getASTContext();
TypedefNameDecl *OrigDecl = TL.getTypedefNameDecl();
TypedefNameDecl *Decl = OrigDecl;
// Transform the underlying type of the typedef and clone the Decl only if
// the typedef has a dependent context.
bool InDependentContext = OrigDecl->getDeclContext()->isDependentContext();
// A typedef/alias Decl within the NestedPattern may reference the outer
// template parameters. They're substituted with corresponding instantiation
// arguments here and in RebuildTemplateSpecializationType() above.
// Otherwise, we would have a CTAD guide with "dangling" template
// parameters.
// For example,
// template <class T> struct Outer {
// using Alias = S<T>;
// template <class U> struct Inner {
// Inner(Alias);
// };
// };
if (OuterInstantiationArgs && InDependentContext &&
TL.getTypePtr()->isInstantiationDependentType()) {
Decl = cast_if_present<TypedefNameDecl>(
TypedefNameInstantiator->InstantiateTypedefNameDecl(
OrigDecl, /*IsTypeAlias=*/isa<TypeAliasDecl>(OrigDecl)));
if (!Decl)
return QualType();
MaterializedTypedefs.push_back(Decl);
} else if (InDependentContext) {
TypeLocBuilder InnerTLB;
QualType Transformed =
TransformType(InnerTLB, OrigDecl->getTypeSourceInfo()->getTypeLoc());
TypeSourceInfo *TSI = InnerTLB.getTypeSourceInfo(Context, Transformed);
if (isa<TypeAliasDecl>(OrigDecl))
Decl = TypeAliasDecl::Create(
Context, Context.getTranslationUnitDecl(), OrigDecl->getBeginLoc(),
OrigDecl->getLocation(), OrigDecl->getIdentifier(), TSI);
else {
assert(isa<TypedefDecl>(OrigDecl) && "Not a Type alias or typedef");
Decl = TypedefDecl::Create(
Context, Context.getTranslationUnitDecl(), OrigDecl->getBeginLoc(),
OrigDecl->getLocation(), OrigDecl->getIdentifier(), TSI);
}
MaterializedTypedefs.push_back(Decl);
}
QualType TDTy = Context.getTypedefType(Decl);
TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(TDTy);
TypedefTL.setNameLoc(TL.getNameLoc());
return TDTy;
}
};
// Build a deduction guide using the provided information.
//
// A deduction guide can be either a template or a non-template function
// declaration. If \p TemplateParams is null, a non-template function
// declaration will be created.
NamedDecl *
buildDeductionGuide(Sema &SemaRef, TemplateDecl *OriginalTemplate,
TemplateParameterList *TemplateParams,
CXXConstructorDecl *Ctor, ExplicitSpecifier ES,
TypeSourceInfo *TInfo, SourceLocation LocStart,
SourceLocation Loc, SourceLocation LocEnd, bool IsImplicit,
llvm::ArrayRef<TypedefNameDecl *> MaterializedTypedefs = {},
const AssociatedConstraint &FunctionTrailingRC = {}) {
DeclContext *DC = OriginalTemplate->getDeclContext();
auto DeductionGuideName =
SemaRef.Context.DeclarationNames.getCXXDeductionGuideName(
OriginalTemplate);
DeclarationNameInfo Name(DeductionGuideName, Loc);
ArrayRef<ParmVarDecl *> Params =
TInfo->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams();
// Build the implicit deduction guide template.
auto *Guide = CXXDeductionGuideDecl::Create(
SemaRef.Context, DC, LocStart, ES, Name, TInfo->getType(), TInfo, LocEnd,
Ctor, DeductionCandidate::Normal, FunctionTrailingRC);
Guide->setImplicit(IsImplicit);
Guide->setParams(Params);
for (auto *Param : Params)
Param->setDeclContext(Guide);
for (auto *TD : MaterializedTypedefs)
TD->setDeclContext(Guide);
if (isa<CXXRecordDecl>(DC))
Guide->setAccess(AS_public);
if (!TemplateParams) {
DC->addDecl(Guide);
return Guide;
}
auto *GuideTemplate = FunctionTemplateDecl::Create(
SemaRef.Context, DC, Loc, DeductionGuideName, TemplateParams, Guide);
GuideTemplate->setImplicit(IsImplicit);
Guide->setDescribedFunctionTemplate(GuideTemplate);
if (isa<CXXRecordDecl>(DC))
GuideTemplate->setAccess(AS_public);
DC->addDecl(GuideTemplate);
return GuideTemplate;
}
// Transform a given template type parameter `TTP`.
TemplateTypeParmDecl *transformTemplateTypeParam(
Sema &SemaRef, DeclContext *DC, TemplateTypeParmDecl *TTP,
MultiLevelTemplateArgumentList &Args, unsigned NewDepth, unsigned NewIndex,
bool EvaluateConstraint) {
// TemplateTypeParmDecl's index cannot be changed after creation, so
// substitute it directly.
auto *NewTTP = TemplateTypeParmDecl::Create(
SemaRef.Context, DC, TTP->getBeginLoc(), TTP->getLocation(), NewDepth,
NewIndex, TTP->getIdentifier(), TTP->wasDeclaredWithTypename(),
TTP->isParameterPack(), TTP->hasTypeConstraint(),
TTP->getNumExpansionParameters());
if (const auto *TC = TTP->getTypeConstraint())
SemaRef.SubstTypeConstraint(NewTTP, TC, Args,
/*EvaluateConstraint=*/EvaluateConstraint);
if (TTP->hasDefaultArgument()) {
TemplateArgumentLoc InstantiatedDefaultArg;
if (!SemaRef.SubstTemplateArgument(
TTP->getDefaultArgument(), Args, InstantiatedDefaultArg,
TTP->getDefaultArgumentLoc(), TTP->getDeclName()))
NewTTP->setDefaultArgument(SemaRef.Context, InstantiatedDefaultArg);
}
SemaRef.CurrentInstantiationScope->InstantiatedLocal(TTP, NewTTP);
return NewTTP;
}
// Similar to above, but for non-type template or template template parameters.
template <typename NonTypeTemplateOrTemplateTemplateParmDecl>
NonTypeTemplateOrTemplateTemplateParmDecl *
transformTemplateParam(Sema &SemaRef, DeclContext *DC,
NonTypeTemplateOrTemplateTemplateParmDecl *OldParam,
MultiLevelTemplateArgumentList &Args, unsigned NewIndex,
unsigned NewDepth) {
// Ask the template instantiator to do the heavy lifting for us, then adjust
// the index of the parameter once it's done.
auto *NewParam = cast<NonTypeTemplateOrTemplateTemplateParmDecl>(
SemaRef.SubstDecl(OldParam, DC, Args));
NewParam->setPosition(NewIndex);
NewParam->setDepth(NewDepth);
return NewParam;
}
NamedDecl *transformTemplateParameter(Sema &SemaRef, DeclContext *DC,
NamedDecl *TemplateParam,
MultiLevelTemplateArgumentList &Args,
unsigned NewIndex, unsigned NewDepth,
bool EvaluateConstraint = true) {
if (auto *TTP = dyn_cast<TemplateTypeParmDecl>(TemplateParam))
return transformTemplateTypeParam(
SemaRef, DC, TTP, Args, NewDepth, NewIndex,
/*EvaluateConstraint=*/EvaluateConstraint);
if (auto *TTP = dyn_cast<TemplateTemplateParmDecl>(TemplateParam))
return transformTemplateParam(SemaRef, DC, TTP, Args, NewIndex, NewDepth);
if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(TemplateParam))
return transformTemplateParam(SemaRef, DC, NTTP, Args, NewIndex, NewDepth);
llvm_unreachable("Unhandled template parameter types");
}
/// Transform to convert portions of a constructor declaration into the
/// corresponding deduction guide, per C++1z [over.match.class.deduct]p1.
struct ConvertConstructorToDeductionGuideTransform {
ConvertConstructorToDeductionGuideTransform(Sema &S,
ClassTemplateDecl *Template)
: SemaRef(S), Template(Template) {
// If the template is nested, then we need to use the original
// pattern to iterate over the constructors.
ClassTemplateDecl *Pattern = Template;
while (Pattern->getInstantiatedFromMemberTemplate()) {
if (Pattern->isMemberSpecialization())
break;
Pattern = Pattern->getInstantiatedFromMemberTemplate();
NestedPattern = Pattern;
}
if (NestedPattern)
OuterInstantiationArgs = SemaRef.getTemplateInstantiationArgs(Template);
}
Sema &SemaRef;
ClassTemplateDecl *Template;
ClassTemplateDecl *NestedPattern = nullptr;
DeclContext *DC = Template->getDeclContext();
CXXRecordDecl *Primary = Template->getTemplatedDecl();
DeclarationName DeductionGuideName =
SemaRef.Context.DeclarationNames.getCXXDeductionGuideName(Template);
QualType DeducedType = SemaRef.Context.getTypeDeclType(Primary);
// Index adjustment to apply to convert depth-1 template parameters into
// depth-0 template parameters.
unsigned Depth1IndexAdjustment = Template->getTemplateParameters()->size();
// Instantiation arguments for the outermost depth-1 templates
// when the template is nested
MultiLevelTemplateArgumentList OuterInstantiationArgs;
/// Transform a constructor declaration into a deduction guide.
NamedDecl *transformConstructor(FunctionTemplateDecl *FTD,
CXXConstructorDecl *CD) {
SmallVector<TemplateArgument, 16> SubstArgs;
LocalInstantiationScope Scope(SemaRef);
// C++ [over.match.class.deduct]p1:
// -- For each constructor of the class template designated by the
// template-name, a function template with the following properties:
// -- The template parameters are the template parameters of the class
// template followed by the template parameters (including default
// template arguments) of the constructor, if any.
TemplateParameterList *TemplateParams =
SemaRef.GetTemplateParameterList(Template);
SmallVector<TemplateArgument, 16> Depth1Args;
AssociatedConstraint OuterRC(TemplateParams->getRequiresClause());
if (FTD) {
TemplateParameterList *InnerParams = FTD->getTemplateParameters();
SmallVector<NamedDecl *, 16> AllParams;
AllParams.reserve(TemplateParams->size() + InnerParams->size());
AllParams.insert(AllParams.begin(), TemplateParams->begin(),
TemplateParams->end());
SubstArgs.reserve(InnerParams->size());
Depth1Args.reserve(InnerParams->size());
// Later template parameters could refer to earlier ones, so build up
// a list of substituted template arguments as we go.
for (NamedDecl *Param : *InnerParams) {
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(Depth1Args);
Args.addOuterRetainedLevel();
if (NestedPattern)
Args.addOuterRetainedLevels(NestedPattern->getTemplateDepth());
auto [Depth, Index] = getDepthAndIndex(Param);
// Depth can be 0 if FTD belongs to a non-template class/a class
// template specialization with an empty template parameter list. In
// that case, we don't want the NewDepth to overflow, and it should
// remain 0.
NamedDecl *NewParam = transformTemplateParameter(
SemaRef, DC, Param, Args, Index + Depth1IndexAdjustment,
Depth ? Depth - 1 : 0);
if (!NewParam)
return nullptr;
// Constraints require that we substitute depth-1 arguments
// to match depths when substituted for evaluation later
Depth1Args.push_back(SemaRef.Context.getInjectedTemplateArg(NewParam));
if (NestedPattern) {
auto [Depth, Index] = getDepthAndIndex(NewParam);
NewParam = transformTemplateParameter(
SemaRef, DC, NewParam, OuterInstantiationArgs, Index,
Depth - OuterInstantiationArgs.getNumSubstitutedLevels(),
/*EvaluateConstraint=*/false);
}
assert(getDepthAndIndex(NewParam).first == 0 &&
"Unexpected template parameter depth");
AllParams.push_back(NewParam);
SubstArgs.push_back(SemaRef.Context.getInjectedTemplateArg(NewParam));
}
// Substitute new template parameters into requires-clause if present.
Expr *RequiresClause = nullptr;
if (Expr *InnerRC = InnerParams->getRequiresClause()) {
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(Depth1Args);
Args.addOuterRetainedLevel();
if (NestedPattern)
Args.addOuterRetainedLevels(NestedPattern->getTemplateDepth());
ExprResult E =
SemaRef.SubstConstraintExprWithoutSatisfaction(InnerRC, Args);
if (!E.isUsable())
return nullptr;
RequiresClause = E.get();
}
TemplateParams = TemplateParameterList::Create(
SemaRef.Context, InnerParams->getTemplateLoc(),
InnerParams->getLAngleLoc(), AllParams, InnerParams->getRAngleLoc(),
RequiresClause);
}
// If we built a new template-parameter-list, track that we need to
// substitute references to the old parameters into references to the
// new ones.
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
if (FTD) {
Args.addOuterTemplateArguments(SubstArgs);
Args.addOuterRetainedLevel();
}
FunctionProtoTypeLoc FPTL = CD->getTypeSourceInfo()
->getTypeLoc()
.getAsAdjusted<FunctionProtoTypeLoc>();
assert(FPTL && "no prototype for constructor declaration");
// Transform the type of the function, adjusting the return type and
// replacing references to the old parameters with references to the
// new ones.
TypeLocBuilder TLB;
SmallVector<ParmVarDecl *, 8> Params;
SmallVector<TypedefNameDecl *, 4> MaterializedTypedefs;
QualType NewType = transformFunctionProtoType(TLB, FPTL, Params, Args,
MaterializedTypedefs);
if (NewType.isNull())
return nullptr;
TypeSourceInfo *NewTInfo = TLB.getTypeSourceInfo(SemaRef.Context, NewType);
// At this point, the function parameters are already 'instantiated' in the
// current scope. Substitute into the constructor's trailing
// requires-clause, if any.
AssociatedConstraint FunctionTrailingRC;
if (const AssociatedConstraint &RC = CD->getTrailingRequiresClause()) {
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(Depth1Args);
Args.addOuterRetainedLevel();
if (NestedPattern)
Args.addOuterRetainedLevels(NestedPattern->getTemplateDepth());
ExprResult E = SemaRef.SubstConstraintExprWithoutSatisfaction(
const_cast<Expr *>(RC.ConstraintExpr), Args);
if (!E.isUsable())
return nullptr;
FunctionTrailingRC = AssociatedConstraint(E.get(), RC.ArgPackSubstIndex);
}
// C++ [over.match.class.deduct]p1:
// If C is defined, for each constructor of C, a function template with
// the following properties:
// [...]
// - The associated constraints are the conjunction of the associated
// constraints of C and the associated constraints of the constructor, if
// any.
if (OuterRC) {
// The outer template parameters are not transformed, so their
// associated constraints don't need substitution.
// FIXME: Should simply add another field for the OuterRC, instead of
// combining them like this.
if (!FunctionTrailingRC)
FunctionTrailingRC = OuterRC;
else
FunctionTrailingRC = AssociatedConstraint(
BinaryOperator::Create(
SemaRef.Context,
/*lhs=*/const_cast<Expr *>(OuterRC.ConstraintExpr),
/*rhs=*/const_cast<Expr *>(FunctionTrailingRC.ConstraintExpr),
BO_LAnd, SemaRef.Context.BoolTy, VK_PRValue, OK_Ordinary,
TemplateParams->getTemplateLoc(), FPOptionsOverride()),
FunctionTrailingRC.ArgPackSubstIndex);
}
return buildDeductionGuide(
SemaRef, Template, TemplateParams, CD, CD->getExplicitSpecifier(),
NewTInfo, CD->getBeginLoc(), CD->getLocation(), CD->getEndLoc(),
/*IsImplicit=*/true, MaterializedTypedefs, FunctionTrailingRC);
}
/// Build a deduction guide with the specified parameter types.
NamedDecl *buildSimpleDeductionGuide(MutableArrayRef<QualType> ParamTypes) {
SourceLocation Loc = Template->getLocation();
// Build the requested type.
FunctionProtoType::ExtProtoInfo EPI;
EPI.HasTrailingReturn = true;
QualType Result = SemaRef.BuildFunctionType(DeducedType, ParamTypes, Loc,
DeductionGuideName, EPI);
TypeSourceInfo *TSI = SemaRef.Context.getTrivialTypeSourceInfo(Result, Loc);
if (NestedPattern)
TSI = SemaRef.SubstType(TSI, OuterInstantiationArgs, Loc,
DeductionGuideName);
if (!TSI)
return nullptr;
FunctionProtoTypeLoc FPTL =
TSI->getTypeLoc().castAs<FunctionProtoTypeLoc>();
// Build the parameters, needed during deduction / substitution.
SmallVector<ParmVarDecl *, 4> Params;
for (auto T : ParamTypes) {
auto *TSI = SemaRef.Context.getTrivialTypeSourceInfo(T, Loc);
if (NestedPattern)
TSI = SemaRef.SubstType(TSI, OuterInstantiationArgs, Loc,
DeclarationName());
if (!TSI)
return nullptr;
ParmVarDecl *NewParam =
ParmVarDecl::Create(SemaRef.Context, DC, Loc, Loc, nullptr,
TSI->getType(), TSI, SC_None, nullptr);
NewParam->setScopeInfo(0, Params.size());
FPTL.setParam(Params.size(), NewParam);
Params.push_back(NewParam);
}
return buildDeductionGuide(
SemaRef, Template, SemaRef.GetTemplateParameterList(Template), nullptr,
ExplicitSpecifier(), TSI, Loc, Loc, Loc, /*IsImplicit=*/true);
}
private:
QualType transformFunctionProtoType(
TypeLocBuilder &TLB, FunctionProtoTypeLoc TL,
SmallVectorImpl<ParmVarDecl *> &Params,
MultiLevelTemplateArgumentList &Args,
SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs) {
SmallVector<QualType, 4> ParamTypes;
const FunctionProtoType *T = TL.getTypePtr();
// -- The types of the function parameters are those of the constructor.
for (auto *OldParam : TL.getParams()) {
ParmVarDecl *NewParam = OldParam;
// Given
// template <class T> struct C {
// template <class U> struct D {
// template <class V> D(U, V);
// };
// };
// First, transform all the references to template parameters that are
// defined outside of the surrounding class template. That is T in the
// above example.
if (NestedPattern) {
NewParam = transformFunctionTypeParam(
NewParam, OuterInstantiationArgs, MaterializedTypedefs,
/*TransformingOuterPatterns=*/true);
if (!NewParam)
return QualType();
}
// Then, transform all the references to template parameters that are
// defined at the class template and the constructor. In this example,
// they're U and V, respectively.
NewParam =
transformFunctionTypeParam(NewParam, Args, MaterializedTypedefs,
/*TransformingOuterPatterns=*/false);
if (!NewParam)
return QualType();
ParamTypes.push_back(NewParam->getType());
Params.push_back(NewParam);
}
// -- The return type is the class template specialization designated by
// the template-name and template arguments corresponding to the
// template parameters obtained from the class template.
//
// We use the injected-class-name type of the primary template instead.
// This has the convenient property that it is different from any type that
// the user can write in a deduction-guide (because they cannot enter the
// context of the template), so implicit deduction guides can never collide
// with explicit ones.
QualType ReturnType = DeducedType;
TLB.pushTypeSpec(ReturnType).setNameLoc(Primary->getLocation());
// Resolving a wording defect, we also inherit the variadicness of the
// constructor.
FunctionProtoType::ExtProtoInfo EPI;
EPI.Variadic = T->isVariadic();
EPI.HasTrailingReturn = true;
QualType Result = SemaRef.BuildFunctionType(
ReturnType, ParamTypes, TL.getBeginLoc(), DeductionGuideName, EPI);
if (Result.isNull())
return QualType();
FunctionProtoTypeLoc NewTL = TLB.push<FunctionProtoTypeLoc>(Result);
NewTL.setLocalRangeBegin(TL.getLocalRangeBegin());
NewTL.setLParenLoc(TL.getLParenLoc());
NewTL.setRParenLoc(TL.getRParenLoc());
NewTL.setExceptionSpecRange(SourceRange());
NewTL.setLocalRangeEnd(TL.getLocalRangeEnd());
for (unsigned I = 0, E = NewTL.getNumParams(); I != E; ++I)
NewTL.setParam(I, Params[I]);
return Result;
}
ParmVarDecl *transformFunctionTypeParam(
ParmVarDecl *OldParam, MultiLevelTemplateArgumentList &Args,
llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs,
bool TransformingOuterPatterns) {
TypeSourceInfo *OldDI = OldParam->getTypeSourceInfo();
TypeSourceInfo *NewDI;
if (auto PackTL = OldDI->getTypeLoc().getAs<PackExpansionTypeLoc>()) {
// Expand out the one and only element in each inner pack.
Sema::ArgPackSubstIndexRAII SubstIndex(SemaRef, 0u);
NewDI =
SemaRef.SubstType(PackTL.getPatternLoc(), Args,
OldParam->getLocation(), OldParam->getDeclName());
if (!NewDI)
return nullptr;
NewDI =
SemaRef.CheckPackExpansion(NewDI, PackTL.getEllipsisLoc(),
PackTL.getTypePtr()->getNumExpansions());
} else
NewDI = SemaRef.SubstType(OldDI, Args, OldParam->getLocation(),
OldParam->getDeclName());
if (!NewDI)
return nullptr;
// Extract the type. This (for instance) replaces references to typedef
// members of the current instantiations with the definitions of those
// typedefs, avoiding triggering instantiation of the deduced type during
// deduction.
NewDI = ExtractTypeForDeductionGuide(
SemaRef, MaterializedTypedefs, NestedPattern,
TransformingOuterPatterns ? &Args : nullptr)
.transform(NewDI);
// Resolving a wording defect, we also inherit default arguments from the
// constructor.
ExprResult NewDefArg;
if (OldParam->hasDefaultArg()) {
// We don't care what the value is (we won't use it); just create a
// placeholder to indicate there is a default argument.
QualType ParamTy = NewDI->getType();
NewDefArg = new (SemaRef.Context)
OpaqueValueExpr(OldParam->getDefaultArgRange().getBegin(),
ParamTy.getNonLValueExprType(SemaRef.Context),
ParamTy->isLValueReferenceType() ? VK_LValue
: ParamTy->isRValueReferenceType() ? VK_XValue
: VK_PRValue);
}
// Handle arrays and functions decay.
auto NewType = NewDI->getType();
if (NewType->isArrayType() || NewType->isFunctionType())
NewType = SemaRef.Context.getDecayedType(NewType);
ParmVarDecl *NewParam = ParmVarDecl::Create(
SemaRef.Context, DC, OldParam->getInnerLocStart(),
OldParam->getLocation(), OldParam->getIdentifier(), NewType, NewDI,
OldParam->getStorageClass(), NewDefArg.get());
NewParam->setScopeInfo(OldParam->getFunctionScopeDepth(),
OldParam->getFunctionScopeIndex());
SemaRef.CurrentInstantiationScope->InstantiatedLocal(OldParam, NewParam);
return NewParam;
}
};
// Find all template parameters that appear in the given DeducedArgs.
// Return the indices of the template parameters in the TemplateParams.
SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
Sema &SemaRef, const TemplateParameterList *TemplateParamsList,
ArrayRef<TemplateArgument> DeducedArgs) {
llvm::SmallBitVector ReferencedTemplateParams(TemplateParamsList->size());
SemaRef.MarkUsedTemplateParameters(
DeducedArgs, TemplateParamsList->getDepth(), ReferencedTemplateParams);
SmallVector<unsigned> Results;
for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
if (ReferencedTemplateParams[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;
}
// Returns all source deduction guides associated with the declared
// deduction guides that have the specified deduction guide name.
llvm::DenseSet<const NamedDecl *> getSourceDeductionGuides(DeclarationName Name,
DeclContext *DC) {
assert(Name.getNameKind() ==
DeclarationName::NameKind::CXXDeductionGuideName &&
"name must be a deduction guide name");
llvm::DenseSet<const NamedDecl *> Result;
for (auto *D : DC->lookup(Name)) {
if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(D))
D = FTD->getTemplatedDecl();
if (const auto *GD = dyn_cast<CXXDeductionGuideDecl>(D)) {
assert(GD->getSourceDeductionGuide() &&
"deduction guide for alias template must have a source deduction "
"guide");
Result.insert(GD->getSourceDeductionGuide());
}
}
return Result;
}
// Build the associated constraints for the alias deduction guides.
// C++ [over.match.class.deduct]p3.3:
// The associated constraints ([temp.constr.decl]) are the conjunction of the
// associated constraints of g and a constraint that is satisfied if and only
// if the arguments of A are deducible (see below) from the return type.
//
// The return result is expected to be the require-clause for the synthesized
// alias deduction guide.
Expr *
buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
TypeAliasTemplateDecl *AliasTemplate,
ArrayRef<DeducedTemplateArgument> DeduceResults,
unsigned FirstUndeducedParamIdx, Expr *IsDeducible) {
Expr *RC = F->getTemplateParameters()->getRequiresClause();
if (!RC)
return IsDeducible;
ASTContext &Context = SemaRef.Context;
LocalInstantiationScope Scope(SemaRef);
// In the clang AST, constraint nodes are deliberately not instantiated unless
// they are actively being evaluated. Consequently, occurrences of template
// parameters in the require-clause expression have a subtle "depth"
// difference compared to normal occurrences in places, such as function
// parameters. When transforming the require-clause, we must take this
// distinction into account:
//
// 1) In the transformed require-clause, occurrences of template parameters
// must use the "uninstantiated" depth;
// 2) When substituting on the require-clause expr of the underlying
// deduction guide, we must use the entire set of template argument lists;
//
// It's important to note that we're performing this transformation on an
// *instantiated* AliasTemplate.
// For 1), if the alias template is nested within a class template, we
// calcualte the 'uninstantiated' depth by adding the substitution level back.
unsigned AdjustDepth = 0;
if (auto *PrimaryTemplate =
AliasTemplate->getInstantiatedFromMemberTemplate())
AdjustDepth = PrimaryTemplate->getTemplateDepth();
// We rebuild all template parameters with the uninstantiated depth, and
// build template arguments refer to them.
SmallVector<TemplateArgument> AdjustedAliasTemplateArgs;
for (auto *TP : *AliasTemplate->getTemplateParameters()) {
// Rebuild any internal references to earlier parameters and reindex
// as we go.
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(AdjustedAliasTemplateArgs);
NamedDecl *NewParam = transformTemplateParameter(
SemaRef, AliasTemplate->getDeclContext(), TP, Args,
/*NewIndex=*/AdjustedAliasTemplateArgs.size(),
getDepthAndIndex(TP).first + AdjustDepth);
TemplateArgument NewTemplateArgument =
Context.getInjectedTemplateArg(NewParam);
AdjustedAliasTemplateArgs.push_back(NewTemplateArgument);
}
// Template arguments used to transform the template arguments in
// DeducedResults.
SmallVector<TemplateArgument> TemplateArgsForBuildingRC(
F->getTemplateParameters()->size());
// Transform the transformed template args
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(AdjustedAliasTemplateArgs);
for (unsigned Index = 0; Index < DeduceResults.size(); ++Index) {
const auto &D = DeduceResults[Index];
if (D.isNull()) { // non-deduced template parameters of f
NamedDecl *TP = F->getTemplateParameters()->getParam(Index);
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(TemplateArgsForBuildingRC);
// Rebuild the template parameter with updated depth and index.
NamedDecl *NewParam =
transformTemplateParameter(SemaRef, F->getDeclContext(), TP, Args,
/*NewIndex=*/FirstUndeducedParamIdx,
getDepthAndIndex(TP).first + AdjustDepth);
FirstUndeducedParamIdx += 1;
assert(TemplateArgsForBuildingRC[Index].isNull());
TemplateArgsForBuildingRC[Index] =
Context.getInjectedTemplateArg(NewParam);
continue;
}
TemplateArgumentLoc Input =
SemaRef.getTrivialTemplateArgumentLoc(D, QualType(), SourceLocation{});
TemplateArgumentLoc Output;
if (!SemaRef.SubstTemplateArgument(Input, Args, Output)) {
assert(TemplateArgsForBuildingRC[Index].isNull() &&
"InstantiatedArgs must be null before setting");
TemplateArgsForBuildingRC[Index] = Output.getArgument();
}
}
// A list of template arguments for transforming the require-clause of F.
// It must contain the entire set of template argument lists.
MultiLevelTemplateArgumentList ArgsForBuildingRC;
ArgsForBuildingRC.setKind(clang::TemplateSubstitutionKind::Rewrite);
ArgsForBuildingRC.addOuterTemplateArguments(TemplateArgsForBuildingRC);
// For 2), if the underlying deduction guide F is nested in a class template,
// we need the entire template argument list, as the constraint AST in the
// require-clause of F remains completely uninstantiated.
//
// For example:
// template <typename T> // depth 0
// struct Outer {
// template <typename U>
// struct Foo { Foo(U); };
//
// template <typename U> // depth 1
// requires C<U>
// Foo(U) -> Foo<int>;
// };
// template <typename U>
// using AFoo = Outer<int>::Foo<U>;
//
// In this scenario, the deduction guide for `Foo` inside `Outer<int>`:
// - The occurrence of U in the require-expression is [depth:1, index:0]
// - The occurrence of U in the function parameter is [depth:0, index:0]
// - The template parameter of U is [depth:0, index:0]
//
// We add the outer template arguments which is [int] to the multi-level arg
// list to ensure that the occurrence U in `C<U>` will be replaced with int
// during the substitution.
//
// NOTE: The underlying deduction guide F is instantiated -- either from an
// explicitly-written deduction guide member, or from a constructor.
// getInstantiatedFromMemberTemplate() can only handle the former case, so we
// check the DeclContext kind.
if (F->getLexicalDeclContext()->getDeclKind() ==
clang::Decl::ClassTemplateSpecialization) {
auto OuterLevelArgs = SemaRef.getTemplateInstantiationArgs(
F, F->getLexicalDeclContext(),
/*Final=*/false, /*Innermost=*/std::nullopt,
/*RelativeToPrimary=*/true,
/*Pattern=*/nullptr,
/*ForConstraintInstantiation=*/true);
for (auto It : OuterLevelArgs)
ArgsForBuildingRC.addOuterTemplateArguments(It.Args);
}
ExprResult E = SemaRef.SubstExpr(RC, ArgsForBuildingRC);
if (E.isInvalid())
return nullptr;
auto Conjunction =
SemaRef.BuildBinOp(SemaRef.getCurScope(), SourceLocation{},
BinaryOperatorKind::BO_LAnd, E.get(), IsDeducible);
if (Conjunction.isInvalid())
return nullptr;
return Conjunction.getAs<Expr>();
}
// Build the is_deducible constraint for the alias deduction guides.
// [over.match.class.deduct]p3.3:
// ... and a constraint that is satisfied if and only if the arguments
// of A are deducible (see below) from the return type.
Expr *buildIsDeducibleConstraint(Sema &SemaRef,
TypeAliasTemplateDecl *AliasTemplate,
QualType ReturnType,
SmallVector<NamedDecl *> TemplateParams) {
ASTContext &Context = SemaRef.Context;
// Constraint AST nodes must use uninstantiated depth.
if (auto *PrimaryTemplate =
AliasTemplate->getInstantiatedFromMemberTemplate();
PrimaryTemplate && TemplateParams.size() > 0) {
LocalInstantiationScope Scope(SemaRef);
// Adjust the depth for TemplateParams.
unsigned AdjustDepth = PrimaryTemplate->getTemplateDepth();
SmallVector<TemplateArgument> TransformedTemplateArgs;
for (auto *TP : TemplateParams) {
// Rebuild any internal references to earlier parameters and reindex
// as we go.
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(TransformedTemplateArgs);
NamedDecl *NewParam = transformTemplateParameter(
SemaRef, AliasTemplate->getDeclContext(), TP, Args,
/*NewIndex=*/TransformedTemplateArgs.size(),
getDepthAndIndex(TP).first + AdjustDepth);
TemplateArgument NewTemplateArgument =
Context.getInjectedTemplateArg(NewParam);
TransformedTemplateArgs.push_back(NewTemplateArgument);
}
// Transformed the ReturnType to restore the uninstantiated depth.
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(TransformedTemplateArgs);
ReturnType = SemaRef.SubstType(
ReturnType, Args, AliasTemplate->getLocation(),
Context.DeclarationNames.getCXXDeductionGuideName(AliasTemplate));
};
SmallVector<TypeSourceInfo *> IsDeducibleTypeTraitArgs = {
Context.getTrivialTypeSourceInfo(
Context.getDeducedTemplateSpecializationType(
TemplateName(AliasTemplate), /*DeducedType=*/QualType(),
/*IsDependent=*/true)), // template specialization type whose
// arguments will be deduced.
Context.getTrivialTypeSourceInfo(
ReturnType), // type from which template arguments are deduced.
};
return TypeTraitExpr::Create(
Context, Context.getLogicalOperationType(), AliasTemplate->getLocation(),
TypeTrait::BTT_IsDeducible, IsDeducibleTypeTraitArgs,
AliasTemplate->getLocation(), /*Value*/ false);
}
std::pair<TemplateDecl *, llvm::ArrayRef<TemplateArgument>>
getRHSTemplateDeclAndArgs(Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate) {
// Unwrap the sugared ElaboratedType.
auto RhsType = AliasTemplate->getTemplatedDecl()
->getUnderlyingType()
.getSingleStepDesugaredType(SemaRef.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();
}
}
return {Template, AliasRhsTemplateArgs};
}
bool IsNonDeducedArgument(const TemplateArgument &TA) {
// The following cases indicate the template argument is non-deducible:
// 1. The result is null. E.g. When it comes from a default template
// argument that doesn't appear in the alias declaration.
// 2. The template parameter is a pack and that cannot be deduced from
// the arguments within the alias declaration.
// Non-deducible template parameters will persist in the transformed
// deduction guide.
return TA.isNull() ||
(TA.getKind() == TemplateArgument::Pack &&
llvm::any_of(TA.pack_elements(), IsNonDeducedArgument));
}
// Build deduction guides for a type alias template from the given underlying
// deduction guide F.
FunctionTemplateDecl *
BuildDeductionGuideForTypeAlias(Sema &SemaRef,
TypeAliasTemplateDecl *AliasTemplate,
FunctionTemplateDecl *F, SourceLocation Loc) {
LocalInstantiationScope Scope(SemaRef);
Sema::InstantiatingTemplate BuildingDeductionGuides(
SemaRef, AliasTemplate->getLocation(), F,
Sema::InstantiatingTemplate::BuildingDeductionGuidesTag{});
if (BuildingDeductionGuides.isInvalid())
return nullptr;
auto &Context = SemaRef.Context;
auto [Template, AliasRhsTemplateArgs] =
getRHSTemplateDeclAndArgs(SemaRef, AliasTemplate);
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 cause
// 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) {
const auto &D = DeduceResults[Index];
if (!IsNonDeducedArgument(D))
DeducedArgs.push_back(D);
else
NonDeducedTemplateParamsInFIndex.push_back(Index);
}
auto DeducedAliasTemplateParams =
TemplateParamsReferencedInTemplateArgumentList(
SemaRef, AliasTemplate->getTemplateParameters(), DeducedArgs);
// All template arguments null by default.
SmallVector<TemplateArgument> TemplateArgsForBuildingFPrime(
F->getTemplateParameters()->size());
// 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());
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(
SemaRef, AliasTemplate->getDeclContext(), TP, Args,
/*NewIndex=*/FPrimeTemplateParams.size(), getDepthAndIndex(TP).first);
FPrimeTemplateParams.push_back(NewParam);
TemplateArgument NewTemplateArgument =
Context.getInjectedTemplateArg(NewParam);
TransformedDeducedAliasArgs[AliasTemplateParamIdx] = NewTemplateArgument;
}
unsigned FirstUndeducedParamIdx = FPrimeTemplateParams.size();
// To form a deduction guide f' from f, we leverage clang's instantiation
// mechanism, we construct a template argument list where the template
// arguments refer to the newly-created template parameters of f', and
// then apply instantiation on this template argument list to instantiate
// f, this ensures all template parameter occurrences are updated
// correctly.
//
// The template argument list is formed, in order, from
// 1) For the template parameters of the alias, the corresponding deduced
// template arguments
// 2) For the non-deduced template parameters of f. the
// (rebuilt) template arguments corresponding.
//
// Note: the non-deduced template arguments of `f` might refer to arguments
// deduced in 1), as in a type constraint.
MultiLevelTemplateArgumentList Args;
Args.setKind(TemplateSubstitutionKind::Rewrite);
Args.addOuterTemplateArguments(TransformedDeducedAliasArgs);
for (unsigned Index = 0; Index < DeduceResults.size(); ++Index) {
const auto &D = DeduceResults[Index];
if (IsNonDeducedArgument(D)) {
// 2): Non-deduced template parameters would be substituted later.
continue;
}
TemplateArgumentLoc Input =
SemaRef.getTrivialTemplateArgumentLoc(D, QualType(), SourceLocation{});
TemplateArgumentLoc Output;
if (!SemaRef.SubstTemplateArgument(Input, Args, Output)) {
assert(TemplateArgsForBuildingFPrime[Index].isNull() &&
"InstantiatedArgs must be null before setting");
TemplateArgsForBuildingFPrime[Index] = Output.getArgument();
}
}
// Case 2)
// ...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(
SemaRef, F->getDeclContext(), TP, Args, FPrimeTemplateParams.size(),
getDepthAndIndex(TP).first);
FPrimeTemplateParams.push_back(NewParam);
assert(TemplateArgsForBuildingFPrime[FTemplateParamIdx].isNull() &&
"The argument must be null before setting");
TemplateArgsForBuildingFPrime[FTemplateParamIdx] =
Context.getInjectedTemplateArg(NewParam);
}
auto *TemplateArgListForBuildingFPrime =
TemplateArgumentList::CreateCopy(Context, TemplateArgsForBuildingFPrime);
// Form the f' by substituting the template arguments into f.
if (auto *FPrime = SemaRef.InstantiateFunctionDeclaration(
F, TemplateArgListForBuildingFPrime, AliasTemplate->getLocation(),
Sema::CodeSynthesisContext::BuildingDeductionGuides)) {
auto *GG = cast<CXXDeductionGuideDecl>(FPrime);
Expr *IsDeducible = buildIsDeducibleConstraint(
SemaRef, AliasTemplate, FPrime->getReturnType(), FPrimeTemplateParams);
Expr *RequiresClause =
buildAssociatedConstraints(SemaRef, F, AliasTemplate, DeduceResults,
FirstUndeducedParamIdx, IsDeducible);
auto *FPrimeTemplateParamList = TemplateParameterList::Create(
Context, AliasTemplate->getTemplateParameters()->getTemplateLoc(),
AliasTemplate->getTemplateParameters()->getLAngleLoc(),
FPrimeTemplateParams,
AliasTemplate->getTemplateParameters()->getRAngleLoc(),
/*RequiresClause=*/RequiresClause);
auto *Result = cast<FunctionTemplateDecl>(buildDeductionGuide(
SemaRef, AliasTemplate, FPrimeTemplateParamList,
GG->getCorrespondingConstructor(), GG->getExplicitSpecifier(),
GG->getTypeSourceInfo(), AliasTemplate->getBeginLoc(),
AliasTemplate->getLocation(), AliasTemplate->getEndLoc(),
F->isImplicit()));
auto *DGuide = cast<CXXDeductionGuideDecl>(Result->getTemplatedDecl());
DGuide->setDeductionCandidateKind(GG->getDeductionCandidateKind());
DGuide->setSourceDeductionGuide(
cast<CXXDeductionGuideDecl>(F->getTemplatedDecl()));
DGuide->setSourceDeductionGuideKind(
CXXDeductionGuideDecl::SourceDeductionGuideKind::Alias);
return Result;
}
return nullptr;
}
void DeclareImplicitDeductionGuidesForTypeAlias(
Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate, SourceLocation Loc) {
if (AliasTemplate->isInvalidDecl())
return;
auto &Context = SemaRef.Context;
auto [Template, AliasRhsTemplateArgs] =
getRHSTemplateDeclAndArgs(SemaRef, AliasTemplate);
if (!Template)
return;
auto SourceDeductionGuides = getSourceDeductionGuides(
Context.DeclarationNames.getCXXDeductionGuideName(AliasTemplate),
AliasTemplate->getDeclContext());
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) {
if (auto *DG = dyn_cast<CXXDeductionGuideDecl>(G)) {
if (SourceDeductionGuides.contains(DG))
continue;
// The deduction guide is a non-template function decl, we just clone it.
auto *FunctionType =
SemaRef.Context.getTrivialTypeSourceInfo(DG->getType());
FunctionProtoTypeLoc FPTL =
FunctionType->getTypeLoc().castAs<FunctionProtoTypeLoc>();
// Clone the parameters.
for (unsigned I = 0, N = DG->getNumParams(); I != N; ++I) {
const auto *P = DG->getParamDecl(I);
auto *TSI = SemaRef.Context.getTrivialTypeSourceInfo(P->getType());
ParmVarDecl *NewParam = ParmVarDecl::Create(
SemaRef.Context, G->getDeclContext(),
DG->getParamDecl(I)->getBeginLoc(), P->getLocation(), nullptr,
TSI->getType(), TSI, SC_None, nullptr);
NewParam->setScopeInfo(0, I);
FPTL.setParam(I, NewParam);
}
auto *Transformed = cast<CXXDeductionGuideDecl>(buildDeductionGuide(
SemaRef, AliasTemplate, /*TemplateParams=*/nullptr,
/*Constructor=*/nullptr, DG->getExplicitSpecifier(), FunctionType,
AliasTemplate->getBeginLoc(), AliasTemplate->getLocation(),
AliasTemplate->getEndLoc(), DG->isImplicit()));
Transformed->setSourceDeductionGuide(DG);
Transformed->setSourceDeductionGuideKind(
CXXDeductionGuideDecl::SourceDeductionGuideKind::Alias);
// FIXME: Here the synthesized deduction guide is not a templated
// function. Per [dcl.decl]p4, the requires-clause shall be present only
// if the declarator declares a templated function, a bug in standard?
AssociatedConstraint Constraint(buildIsDeducibleConstraint(
SemaRef, AliasTemplate, Transformed->getReturnType(), {}));
if (const AssociatedConstraint &RC = DG->getTrailingRequiresClause()) {
auto Conjunction = SemaRef.BuildBinOp(
SemaRef.getCurScope(), SourceLocation{},
BinaryOperatorKind::BO_LAnd, const_cast<Expr *>(RC.ConstraintExpr),
const_cast<Expr *>(Constraint.ConstraintExpr));
if (!Conjunction.isInvalid()) {
Constraint.ConstraintExpr = Conjunction.getAs<Expr>();
Constraint.ArgPackSubstIndex = RC.ArgPackSubstIndex;
}
}
Transformed->setTrailingRequiresClause(Constraint);
continue;
}
FunctionTemplateDecl *F = dyn_cast<FunctionTemplateDecl>(G);
if (!F || SourceDeductionGuides.contains(F->getTemplatedDecl()))
continue;
// The **aggregate** deduction guides are handled in a different code path
// (DeclareAggregateDeductionGuideFromInitList), which involves the tricky
// cache.
if (cast<CXXDeductionGuideDecl>(F->getTemplatedDecl())
->getDeductionCandidateKind() == DeductionCandidate::Aggregate)
continue;
BuildDeductionGuideForTypeAlias(SemaRef, AliasTemplate, F, Loc);
}
}
// Build an aggregate deduction guide for a type alias template.
FunctionTemplateDecl *DeclareAggregateDeductionGuideForTypeAlias(
Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate,
MutableArrayRef<QualType> ParamTypes, SourceLocation Loc) {
TemplateDecl *RHSTemplate =
getRHSTemplateDeclAndArgs(SemaRef, AliasTemplate).first;
if (!RHSTemplate)
return nullptr;
llvm::SmallVector<TypedefNameDecl *> TypedefDecls;
llvm::SmallVector<QualType> NewParamTypes;
ExtractTypeForDeductionGuide TypeAliasTransformer(SemaRef, TypedefDecls);
for (QualType P : ParamTypes) {
QualType Type = TypeAliasTransformer.TransformType(P);
if (Type.isNull())
return nullptr;
NewParamTypes.push_back(Type);
}
auto *RHSDeductionGuide = SemaRef.DeclareAggregateDeductionGuideFromInitList(
RHSTemplate, NewParamTypes, Loc);
if (!RHSDeductionGuide)
return nullptr;
for (TypedefNameDecl *TD : TypedefDecls)
TD->setDeclContext(RHSDeductionGuide->getTemplatedDecl());
return BuildDeductionGuideForTypeAlias(SemaRef, AliasTemplate,
RHSDeductionGuide, Loc);
}
} // namespace
FunctionTemplateDecl *Sema::DeclareAggregateDeductionGuideFromInitList(
TemplateDecl *Template, MutableArrayRef<QualType> ParamTypes,
SourceLocation Loc) {
llvm::FoldingSetNodeID ID;
ID.AddPointer(Template);
for (auto &T : ParamTypes)
T.getCanonicalType().Profile(ID);
unsigned Hash = ID.ComputeHash();
auto Found = AggregateDeductionCandidates.find(Hash);
if (Found != AggregateDeductionCandidates.end()) {
CXXDeductionGuideDecl *GD = Found->getSecond();
return GD->getDescribedFunctionTemplate();
}
if (auto *AliasTemplate = llvm::dyn_cast<TypeAliasTemplateDecl>(Template)) {
if (auto *FTD = DeclareAggregateDeductionGuideForTypeAlias(
*this, AliasTemplate, ParamTypes, Loc)) {
auto *GD = cast<CXXDeductionGuideDecl>(FTD->getTemplatedDecl());
GD->setDeductionCandidateKind(DeductionCandidate::Aggregate);
AggregateDeductionCandidates[Hash] = GD;
return FTD;
}
}
if (CXXRecordDecl *DefRecord =
cast<CXXRecordDecl>(Template->getTemplatedDecl())->getDefinition()) {
if (TemplateDecl *DescribedTemplate =
DefRecord->getDescribedClassTemplate())
Template = DescribedTemplate;
}
DeclContext *DC = Template->getDeclContext();
if (DC->isDependentContext())
return nullptr;
ConvertConstructorToDeductionGuideTransform Transform(
*this, cast<ClassTemplateDecl>(Template));
if (!isCompleteType(Loc, Transform.DeducedType))
return nullptr;
// In case we were expanding a pack when we attempted to declare deduction
// guides, turn off pack expansion for everything we're about to do.
ArgPackSubstIndexRAII SubstIndex(*this, std::nullopt);
// Create a template instantiation record to track the "instantiation" of
// constructors into deduction guides.
InstantiatingTemplate BuildingDeductionGuides(
*this, Loc, Template,
Sema::InstantiatingTemplate::BuildingDeductionGuidesTag{});
if (BuildingDeductionGuides.isInvalid())
return nullptr;
ClassTemplateDecl *Pattern =
Transform.NestedPattern ? Transform.NestedPattern : Transform.Template;
ContextRAII SavedContext(*this, Pattern->getTemplatedDecl());
auto *FTD = cast<FunctionTemplateDecl>(
Transform.buildSimpleDeductionGuide(ParamTypes));
SavedContext.pop();
auto *GD = cast<CXXDeductionGuideDecl>(FTD->getTemplatedDecl());
GD->setDeductionCandidateKind(DeductionCandidate::Aggregate);
AggregateDeductionCandidates[Hash] = GD;
return FTD;
}
void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
SourceLocation Loc) {
if (auto *AliasTemplate = llvm::dyn_cast<TypeAliasTemplateDecl>(Template)) {
DeclareImplicitDeductionGuidesForTypeAlias(*this, AliasTemplate, Loc);
return;
}
if (CXXRecordDecl *DefRecord =
cast<CXXRecordDecl>(Template->getTemplatedDecl())->getDefinition()) {
if (TemplateDecl *DescribedTemplate =
DefRecord->getDescribedClassTemplate())
Template = DescribedTemplate;
}
DeclContext *DC = Template->getDeclContext();
if (DC->isDependentContext())
return;
ConvertConstructorToDeductionGuideTransform Transform(
*this, cast<ClassTemplateDecl>(Template));
if (!isCompleteType(Loc, Transform.DeducedType))
return;
if (hasDeclaredDeductionGuides(Transform.DeductionGuideName, DC))
return;
// In case we were expanding a pack when we attempted to declare deduction
// guides, turn off pack expansion for everything we're about to do.
ArgPackSubstIndexRAII SubstIndex(*this, std::nullopt);
// Create a template instantiation record to track the "instantiation" of
// constructors into deduction guides.
InstantiatingTemplate BuildingDeductionGuides(
*this, Loc, Template,
Sema::InstantiatingTemplate::BuildingDeductionGuidesTag{});
if (BuildingDeductionGuides.isInvalid())
return;
// Convert declared constructors into deduction guide templates.
// FIXME: Skip constructors for which deduction must necessarily fail (those
// for which some class template parameter without a default argument never
// appears in a deduced context).
ClassTemplateDecl *Pattern =
Transform.NestedPattern ? Transform.NestedPattern : Transform.Template;
ContextRAII SavedContext(*this, Pattern->getTemplatedDecl());
llvm::SmallPtrSet<NamedDecl *, 8> ProcessedCtors;
bool AddedAny = false;
for (NamedDecl *D : LookupConstructors(Pattern->getTemplatedDecl())) {
D = D->getUnderlyingDecl();
if (D->isInvalidDecl() || D->isImplicit())
continue;
D = cast<NamedDecl>(D->getCanonicalDecl());
// Within C++20 modules, we may have multiple same constructors in
// multiple same RecordDecls. And it doesn't make sense to create
// duplicated deduction guides for the duplicated constructors.
if (ProcessedCtors.count(D))
continue;
auto *FTD = dyn_cast<FunctionTemplateDecl>(D);
auto *CD =
dyn_cast_or_null<CXXConstructorDecl>(FTD ? FTD->getTemplatedDecl() : D);
// Class-scope explicit specializations (MS extension) do not result in
// deduction guides.
if (!CD || (!FTD && CD->isFunctionTemplateSpecialization()))
continue;
// Cannot make a deduction guide when unparsed arguments are present.
if (llvm::any_of(CD->parameters(), [](ParmVarDecl *P) {
return !P || P->hasUnparsedDefaultArg();
}))
continue;
ProcessedCtors.insert(D);
Transform.transformConstructor(FTD, CD);
AddedAny = true;
}
// C++17 [over.match.class.deduct]
// -- If C is not defined or does not declare any constructors, an
// additional function template derived as above from a hypothetical
// constructor C().
if (!AddedAny)
Transform.buildSimpleDeductionGuide({});
// -- An additional function template derived as above from a hypothetical
// constructor C(C), called the copy deduction candidate.
cast<CXXDeductionGuideDecl>(
cast<FunctionTemplateDecl>(
Transform.buildSimpleDeductionGuide(Transform.DeducedType))
->getTemplatedDecl())
->setDeductionCandidateKind(DeductionCandidate::Copy);
SavedContext.pop();
}
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