llvm/clang/lib/Sema/SemaTemplateDeduction.cpp

//===- SemaTemplateDeduction.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 C++ template argument deduction.
//
//===----------------------------------------------------------------------===//

#include "TreeTransform.h"
#include "TypeLocBuilder.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclAccessPair.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/NestedNameSpecifier.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/TemplateName.h"
#include "clang/AST/Type.h"
#include "clang/AST/TypeLoc.h"
#include "clang/AST/TypeOrdering.h"
#include "clang/AST/UnresolvedSet.h"
#include "clang/Basic/AddressSpaces.h"
#include "clang/Basic/ExceptionSpecificationType.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/Specifiers.h"
#include "clang/Sema/EnterExpressionEvaluationContext.h"
#include "clang/Sema/Ownership.h"
#include "clang/Sema/Sema.h"
#include "clang/Sema/Template.h"
#include "clang/Sema/TemplateDeduction.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
#include <optional>
#include <tuple>
#include <type_traits>
#include <utility>

namespace clang {

  /// Various flags that control template argument deduction.
  ///
  /// These flags can be bitwise-OR'd together.
  enum TemplateDeductionFlags {};
}

usingnamespaceclang;
usingnamespacesema;

/// Compare two APSInts, extending and switching the sign as
/// necessary to compare their values regardless of underlying type.
static bool hasSameExtendedValue(llvm::APSInt X, llvm::APSInt Y) {}

/// The kind of PartialOrdering we're performing template argument deduction
/// for (C++11 [temp.deduct.partial]).
enum class PartialOrderingKind {};

static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch(
    Sema &S, TemplateParameterList *TemplateParams, QualType Param,
    QualType Arg, TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced, unsigned TDF,
    PartialOrderingKind POK, bool DeducedFromArrayBound,
    bool *HasDeducedAnyParam);

enum class PackFold {};
static TemplateDeductionResult
DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
                        ArrayRef<TemplateArgument> Ps,
                        ArrayRef<TemplateArgument> As,
                        TemplateDeductionInfo &Info,
                        SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                        bool NumberOfArgumentsMustMatch, bool PartialOrdering,
                        PackFold PackFold, bool *HasDeducedAnyParam);

static void MarkUsedTemplateParameters(ASTContext &Ctx,
                                       const TemplateArgument &TemplateArg,
                                       bool OnlyDeduced, unsigned Depth,
                                       llvm::SmallBitVector &Used);

static void MarkUsedTemplateParameters(ASTContext &Ctx, QualType T,
                                       bool OnlyDeduced, unsigned Level,
                                       llvm::SmallBitVector &Deduced);

/// 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.
static const NonTypeTemplateParmDecl *
getDeducedParameterFromExpr(const Expr *E, unsigned Depth) {}

static const NonTypeTemplateParmDecl *
getDeducedParameterFromExpr(TemplateDeductionInfo &Info, Expr *E) {}

/// Determine whether two declaration pointers refer to the same
/// declaration.
static bool isSameDeclaration(Decl *X, Decl *Y) {}

/// Verify that the given, deduced template arguments are compatible.
///
/// \returns The deduced template argument, or a NULL template argument if
/// the deduced template arguments were incompatible.
static DeducedTemplateArgument
checkDeducedTemplateArguments(ASTContext &Context,
                              const DeducedTemplateArgument &X,
                              const DeducedTemplateArgument &Y,
                              bool AggregateCandidateDeduction = false) {}

/// Deduce the value of the given non-type template parameter
/// as the given deduced template argument. All non-type template parameter
/// deduction is funneled through here.
static TemplateDeductionResult
DeduceNonTypeTemplateArgument(Sema &S, TemplateParameterList *TemplateParams,
                              const NonTypeTemplateParmDecl *NTTP,
                              const DeducedTemplateArgument &NewDeduced,
                              QualType ValueType, TemplateDeductionInfo &Info,
                              bool PartialOrdering,
                              SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                              bool *HasDeducedAnyParam) {}

/// Deduce the value of the given non-type template parameter
/// from the given integral constant.
static TemplateDeductionResult DeduceNonTypeTemplateArgument(
    Sema &S, TemplateParameterList *TemplateParams,
    const NonTypeTemplateParmDecl *NTTP, const llvm::APSInt &Value,
    QualType ValueType, bool DeducedFromArrayBound, TemplateDeductionInfo &Info,
    bool PartialOrdering, SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    bool *HasDeducedAnyParam) {}

/// Deduce the value of the given non-type template parameter
/// from the given null pointer template argument type.
static TemplateDeductionResult
DeduceNullPtrTemplateArgument(Sema &S, TemplateParameterList *TemplateParams,
                              const NonTypeTemplateParmDecl *NTTP,
                              QualType NullPtrType, TemplateDeductionInfo &Info,
                              bool PartialOrdering,
                              SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                              bool *HasDeducedAnyParam) {}

/// Deduce the value of the given non-type template parameter
/// from the given type- or value-dependent expression.
///
/// \returns true if deduction succeeded, false otherwise.
static TemplateDeductionResult
DeduceNonTypeTemplateArgument(Sema &S, TemplateParameterList *TemplateParams,
                              const NonTypeTemplateParmDecl *NTTP, Expr *Value,
                              TemplateDeductionInfo &Info, bool PartialOrdering,
                              SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                              bool *HasDeducedAnyParam) {}

/// Deduce the value of the given non-type template parameter
/// from the given declaration.
///
/// \returns true if deduction succeeded, false otherwise.
static TemplateDeductionResult
DeduceNonTypeTemplateArgument(Sema &S, TemplateParameterList *TemplateParams,
                              const NonTypeTemplateParmDecl *NTTP, ValueDecl *D,
                              QualType T, TemplateDeductionInfo &Info,
                              bool PartialOrdering,
                              SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                              bool *HasDeducedAnyParam) {}

static TemplateDeductionResult DeduceTemplateArguments(
    Sema &S, TemplateParameterList *TemplateParams, TemplateName Param,
    TemplateName Arg, TemplateDeductionInfo &Info,
    ArrayRef<TemplateArgument> DefaultArguments, bool PartialOrdering,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    bool *HasDeducedAnyParam) {}

/// Deduce the template arguments by comparing the template parameter
/// type (which is a template-id) with the template argument type.
///
/// \param S the Sema
///
/// \param TemplateParams the template parameters that we are deducing
///
/// \param P the parameter type
///
/// \param A the argument type
///
/// \param Info information about the template argument deduction itself
///
/// \param Deduced the deduced template arguments
///
/// \returns the result of template argument deduction so far. Note that a
/// "success" result means that template argument deduction has not yet failed,
/// but it may still fail, later, for other reasons.

static const TemplateSpecializationType *getLastTemplateSpecType(QualType QT) {}

static TemplateDeductionResult
DeduceTemplateSpecArguments(Sema &S, TemplateParameterList *TemplateParams,
                            const QualType P, QualType A,
                            TemplateDeductionInfo &Info, bool PartialOrdering,
                            SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                            bool *HasDeducedAnyParam) {}

static bool IsPossiblyOpaquelyQualifiedTypeInternal(const Type *T) {}

/// Determines whether the given type is an opaque type that
/// might be more qualified when instantiated.
static bool IsPossiblyOpaquelyQualifiedType(QualType T) {}

/// Helper function to build a TemplateParameter when we don't
/// know its type statically.
static TemplateParameter makeTemplateParameter(Decl *D) {}

/// A pack that we're currently deducing.
struct clang::DeducedPack {};

namespace {

/// A scope in which we're performing pack deduction.
class PackDeductionScope {};

} // namespace

template <class T>
static TemplateDeductionResult DeduceForEachType(
    Sema &S, TemplateParameterList *TemplateParams, ArrayRef<QualType> Params,
    ArrayRef<QualType> Args, TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced, PartialOrderingKind POK,
    bool FinishingDeduction, T &&DeductFunc) {}

/// Deduce the template arguments by comparing the list of parameter
/// types to the list of argument types, as in the parameter-type-lists of
/// function types (C++ [temp.deduct.type]p10).
///
/// \param S The semantic analysis object within which we are deducing
///
/// \param TemplateParams The template parameters that we are deducing
///
/// \param Params The list of parameter types
///
/// \param Args The list of argument types
///
/// \param Info information about the template argument deduction itself
///
/// \param Deduced the deduced template arguments
///
/// \param TDF bitwise OR of the TemplateDeductionFlags bits that describe
/// how template argument deduction is performed.
///
/// \param PartialOrdering If true, we are performing template argument
/// deduction for during partial ordering for a call
/// (C++0x [temp.deduct.partial]).
///
/// \param HasDeducedAnyParam If set, the object pointed at will indicate
/// whether any template parameter was deduced.
///
/// \param HasDeducedParam If set, the bit vector will be used to represent
/// which template parameters were deduced, in order.
///
/// \returns the result of template argument deduction so far. Note that a
/// "success" result means that template argument deduction has not yet failed,
/// but it may still fail, later, for other reasons.
static TemplateDeductionResult DeduceTemplateArguments(
    Sema &S, TemplateParameterList *TemplateParams, ArrayRef<QualType> Params,
    ArrayRef<QualType> Args, TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced, unsigned TDF,
    PartialOrderingKind POK, bool *HasDeducedAnyParam,
    llvm::SmallBitVector *HasDeducedParam) {}

/// Determine whether the parameter has qualifiers that the argument
/// lacks. Put another way, determine whether there is no way to add
/// a deduced set of qualifiers to the ParamType that would result in
/// its qualifiers matching those of the ArgType.
static bool hasInconsistentOrSupersetQualifiersOf(QualType ParamType,
                                                  QualType ArgType) {}

bool Sema::isSameOrCompatibleFunctionType(QualType P, QualType A) {}

/// Get the index of the first template parameter that was originally from the
/// innermost template-parameter-list. This is 0 except when we concatenate
/// the template parameter lists of a class template and a constructor template
/// when forming an implicit deduction guide.
static unsigned getFirstInnerIndex(FunctionTemplateDecl *FTD) {}

/// Determine whether a type denotes a forwarding reference.
static bool isForwardingReference(QualType Param, unsigned FirstInnerIndex) {}

///  Attempt to deduce the template arguments by checking the base types
///  according to (C++20 [temp.deduct.call] p4b3.
///
/// \param S the semantic analysis object within which we are deducing.
///
/// \param RD the top level record object we are deducing against.
///
/// \param TemplateParams the template parameters that we are deducing.
///
/// \param P the template specialization parameter type.
///
/// \param Info information about the template argument deduction itself.
///
/// \param Deduced the deduced template arguments.
///
/// \returns the result of template argument deduction with the bases. "invalid"
/// means no matches, "success" found a single item, and the
/// "MiscellaneousDeductionFailure" result happens when the match is ambiguous.
static TemplateDeductionResult
DeduceTemplateBases(Sema &S, const CXXRecordDecl *RD,
                    TemplateParameterList *TemplateParams, QualType P,
                    TemplateDeductionInfo &Info, bool PartialOrdering,
                    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                    bool *HasDeducedAnyParam) {}

/// When propagating a partial ordering kind into a NonCall context,
/// this is used to downgrade a 'Call' into a 'NonCall', so that
/// the kind still reflects whether we are in a partial ordering context.
static PartialOrderingKind
degradeCallPartialOrderingKind(PartialOrderingKind POK) {}

/// Deduce the template arguments by comparing the parameter type and
/// the argument type (C++ [temp.deduct.type]).
///
/// \param S the semantic analysis object within which we are deducing
///
/// \param TemplateParams the template parameters that we are deducing
///
/// \param P the parameter type
///
/// \param A the argument type
///
/// \param Info information about the template argument deduction itself
///
/// \param Deduced the deduced template arguments
///
/// \param TDF bitwise OR of the TemplateDeductionFlags bits that describe
/// how template argument deduction is performed.
///
/// \param PartialOrdering Whether we're performing template argument deduction
/// in the context of partial ordering (C++0x [temp.deduct.partial]).
///
/// \returns the result of template argument deduction so far. Note that a
/// "success" result means that template argument deduction has not yet failed,
/// but it may still fail, later, for other reasons.
static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch(
    Sema &S, TemplateParameterList *TemplateParams, QualType P, QualType A,
    TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced, unsigned TDF,
    PartialOrderingKind POK, bool DeducedFromArrayBound,
    bool *HasDeducedAnyParam) {}

static TemplateDeductionResult
DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
                        const TemplateArgument &P, TemplateArgument A,
                        TemplateDeductionInfo &Info, bool PartialOrdering,
                        SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                        bool *HasDeducedAnyParam) {}

/// Determine whether there is a template argument to be used for
/// deduction.
///
/// This routine "expands" argument packs in-place, overriding its input
/// parameters so that \c Args[ArgIdx] will be the available template argument.
///
/// \returns true if there is another template argument (which will be at
/// \c Args[ArgIdx]), false otherwise.
static bool hasTemplateArgumentForDeduction(ArrayRef<TemplateArgument> &Args,
                                            unsigned &ArgIdx) {}

/// Determine whether the given set of template arguments has a pack
/// expansion that is not the last template argument.
static bool hasPackExpansionBeforeEnd(ArrayRef<TemplateArgument> Args) {}

static TemplateDeductionResult
DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
                        ArrayRef<TemplateArgument> Ps,
                        ArrayRef<TemplateArgument> As,
                        TemplateDeductionInfo &Info,
                        SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                        bool NumberOfArgumentsMustMatch, bool PartialOrdering,
                        PackFold PackFold, bool *HasDeducedAnyParam) {}

TemplateDeductionResult Sema::DeduceTemplateArguments(
    TemplateParameterList *TemplateParams, ArrayRef<TemplateArgument> Ps,
    ArrayRef<TemplateArgument> As, sema::TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    bool NumberOfArgumentsMustMatch) {}

/// Determine whether two template arguments are the same.
static bool isSameTemplateArg(ASTContext &Context,
                              TemplateArgument X,
                              const TemplateArgument &Y,
                              bool PartialOrdering,
                              bool PackExpansionMatchesPack = false) {}

TemplateArgumentLoc
Sema::getTrivialTemplateArgumentLoc(const TemplateArgument &Arg,
                                    QualType NTTPType, SourceLocation Loc,
                                    NamedDecl *TemplateParam) {}

TemplateArgumentLoc
Sema::getIdentityTemplateArgumentLoc(NamedDecl *TemplateParm,
                                     SourceLocation Location) {}

/// Convert the given deduced template argument and add it to the set of
/// fully-converted template arguments.
static bool ConvertDeducedTemplateArgument(
    Sema &S, NamedDecl *Param, DeducedTemplateArgument Arg, NamedDecl *Template,
    TemplateDeductionInfo &Info, bool IsDeduced,
    SmallVectorImpl<TemplateArgument> &SugaredOutput,
    SmallVectorImpl<TemplateArgument> &CanonicalOutput) {}

// FIXME: This should not be a template, but
// ClassTemplatePartialSpecializationDecl sadly does not derive from
// TemplateDecl.
/// \param IsIncomplete When used, we only consider template parameters that
/// were deduced, disregarding any default arguments. After the function
/// finishes, the object pointed at will contain a value indicating if the
/// conversion was actually incomplete.
template <typename TemplateDeclT>
static TemplateDeductionResult ConvertDeducedTemplateArguments(
    Sema &S, TemplateDeclT *Template, bool IsDeduced,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    TemplateDeductionInfo &Info,
    SmallVectorImpl<TemplateArgument> &SugaredBuilder,
    SmallVectorImpl<TemplateArgument> &CanonicalBuilder,
    LocalInstantiationScope *CurrentInstantiationScope = nullptr,
    unsigned NumAlreadyConverted = 0, bool *IsIncomplete = nullptr) {}

static DeclContext *getAsDeclContextOrEnclosing(Decl *D) {}

template<typename T> struct IsPartialSpecialization {};
template<>
struct IsPartialSpecialization<ClassTemplatePartialSpecializationDecl> {};
template<>
struct IsPartialSpecialization<VarTemplatePartialSpecializationDecl> {};

template <typename TemplateDeclT>
static TemplateDeductionResult
CheckDeducedArgumentConstraints(Sema &S, TemplateDeclT *Template,
                                ArrayRef<TemplateArgument> SugaredDeducedArgs,
                                ArrayRef<TemplateArgument> CanonicalDeducedArgs,
                                TemplateDeductionInfo &Info) {}

/// Complete template argument deduction for a partial specialization.
template <typename T>
static std::enable_if_t<IsPartialSpecialization<T>::value,
                        TemplateDeductionResult>
FinishTemplateArgumentDeduction(
    Sema &S, T *Partial, bool IsPartialOrdering,
    ArrayRef<TemplateArgument> TemplateArgs,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    TemplateDeductionInfo &Info) {}

/// Complete template argument deduction for a class or variable template,
/// when partial ordering against a partial specialization.
// FIXME: Factor out duplication with partial specialization version above.
static TemplateDeductionResult FinishTemplateArgumentDeduction(
    Sema &S, TemplateDecl *Template, bool PartialOrdering,
    ArrayRef<TemplateArgument> TemplateArgs,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    TemplateDeductionInfo &Info) {}

/// Complete template argument deduction for DeduceTemplateArgumentsFromType.
/// FIXME: this is mostly duplicated with the above two versions. Deduplicate
/// the three implementations.
static TemplateDeductionResult FinishTemplateArgumentDeduction(
    Sema &S, TemplateDecl *TD,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    TemplateDeductionInfo &Info) {}

/// Perform template argument deduction to determine whether the given template
/// arguments match the given class or variable template partial specialization
/// per C++ [temp.class.spec.match].
template <typename T>
static std::enable_if_t<IsPartialSpecialization<T>::value,
                        TemplateDeductionResult>
DeduceTemplateArguments(Sema &S, T *Partial,
                        ArrayRef<TemplateArgument> TemplateArgs,
                        TemplateDeductionInfo &Info) {}

TemplateDeductionResult
Sema::DeduceTemplateArguments(ClassTemplatePartialSpecializationDecl *Partial,
                              ArrayRef<TemplateArgument> TemplateArgs,
                              TemplateDeductionInfo &Info) {}
TemplateDeductionResult
Sema::DeduceTemplateArguments(VarTemplatePartialSpecializationDecl *Partial,
                              ArrayRef<TemplateArgument> TemplateArgs,
                              TemplateDeductionInfo &Info) {}

TemplateDeductionResult
Sema::DeduceTemplateArgumentsFromType(TemplateDecl *TD, QualType FromType,
                                      sema::TemplateDeductionInfo &Info) {}

/// Determine whether the given type T is a simple-template-id type.
static bool isSimpleTemplateIdType(QualType T) {}

TemplateDeductionResult Sema::SubstituteExplicitTemplateArguments(
    FunctionTemplateDecl *FunctionTemplate,
    TemplateArgumentListInfo &ExplicitTemplateArgs,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    SmallVectorImpl<QualType> &ParamTypes, QualType *FunctionType,
    TemplateDeductionInfo &Info) {}

/// Check whether the deduced argument type for a call to a function
/// template matches the actual argument type per C++ [temp.deduct.call]p4.
static TemplateDeductionResult
CheckOriginalCallArgDeduction(Sema &S, TemplateDeductionInfo &Info,
                              Sema::OriginalCallArg OriginalArg,
                              QualType DeducedA) {}

/// Find the pack index for a particular parameter index in an instantiation of
/// a function template with specific arguments.
///
/// \return The pack index for whichever pack produced this parameter, or -1
///         if this was not produced by a parameter. Intended to be used as the
///         ArgumentPackSubstitutionIndex for further substitutions.
// FIXME: We should track this in OriginalCallArgs so we don't need to
// reconstruct it here.
static unsigned getPackIndexForParam(Sema &S,
                                     FunctionTemplateDecl *FunctionTemplate,
                                     const MultiLevelTemplateArgumentList &Args,
                                     unsigned ParamIdx) {}

// if `Specialization` is a `CXXConstructorDecl` or `CXXConversionDecl`,
// we'll try to instantiate and update its explicit specifier after constraint
// checking.
static TemplateDeductionResult instantiateExplicitSpecifierDeferred(
    Sema &S, FunctionDecl *Specialization,
    const MultiLevelTemplateArgumentList &SubstArgs,
    TemplateDeductionInfo &Info, FunctionTemplateDecl *FunctionTemplate,
    ArrayRef<TemplateArgument> DeducedArgs) {}

TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
    FunctionTemplateDecl *FunctionTemplate,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    unsigned NumExplicitlySpecified, FunctionDecl *&Specialization,
    TemplateDeductionInfo &Info,
    SmallVectorImpl<OriginalCallArg> const *OriginalCallArgs,
    bool PartialOverloading, llvm::function_ref<bool()> CheckNonDependent) {}

/// Gets the type of a function for template-argument-deducton
/// purposes when it's considered as part of an overload set.
static QualType GetTypeOfFunction(Sema &S, const OverloadExpr::FindResult &R,
                                  FunctionDecl *Fn) {}

/// Apply the deduction rules for overload sets.
///
/// \return the null type if this argument should be treated as an
/// undeduced context
static QualType
ResolveOverloadForDeduction(Sema &S, TemplateParameterList *TemplateParams,
                            Expr *Arg, QualType ParamType,
                            bool ParamWasReference,
                            TemplateSpecCandidateSet *FailedTSC = nullptr) {}

/// Perform the adjustments to the parameter and argument types
/// described in C++ [temp.deduct.call].
///
/// \returns true if the caller should not attempt to perform any template
/// argument deduction based on this P/A pair because the argument is an
/// overloaded function set that could not be resolved.
static bool AdjustFunctionParmAndArgTypesForDeduction(
    Sema &S, TemplateParameterList *TemplateParams, unsigned FirstInnerIndex,
    QualType &ParamType, QualType &ArgType,
    Expr::Classification ArgClassification, Expr *Arg, unsigned &TDF,
    TemplateSpecCandidateSet *FailedTSC = nullptr) {}

static bool
hasDeducibleTemplateParameters(Sema &S, FunctionTemplateDecl *FunctionTemplate,
                               QualType T);

static TemplateDeductionResult DeduceTemplateArgumentsFromCallArgument(
    Sema &S, TemplateParameterList *TemplateParams, unsigned FirstInnerIndex,
    QualType ParamType, QualType ArgType,
    Expr::Classification ArgClassification, Expr *Arg,
    TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    SmallVectorImpl<Sema::OriginalCallArg> &OriginalCallArgs,
    bool DecomposedParam, unsigned ArgIdx, unsigned TDF,
    TemplateSpecCandidateSet *FailedTSC = nullptr);

/// Attempt template argument deduction from an initializer list
///        deemed to be an argument in a function call.
static TemplateDeductionResult DeduceFromInitializerList(
    Sema &S, TemplateParameterList *TemplateParams, QualType AdjustedParamType,
    InitListExpr *ILE, TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    SmallVectorImpl<Sema::OriginalCallArg> &OriginalCallArgs, unsigned ArgIdx,
    unsigned TDF) {}

/// Perform template argument deduction per [temp.deduct.call] for a
///        single parameter / argument pair.
static TemplateDeductionResult DeduceTemplateArgumentsFromCallArgument(
    Sema &S, TemplateParameterList *TemplateParams, unsigned FirstInnerIndex,
    QualType ParamType, QualType ArgType,
    Expr::Classification ArgClassification, Expr *Arg,
    TemplateDeductionInfo &Info,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    SmallVectorImpl<Sema::OriginalCallArg> &OriginalCallArgs,
    bool DecomposedParam, unsigned ArgIdx, unsigned TDF,
    TemplateSpecCandidateSet *FailedTSC) {}

TemplateDeductionResult Sema::DeduceTemplateArguments(
    FunctionTemplateDecl *FunctionTemplate,
    TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
    FunctionDecl *&Specialization, TemplateDeductionInfo &Info,
    bool PartialOverloading, bool AggregateDeductionCandidate,
    QualType ObjectType, Expr::Classification ObjectClassification,
    llvm::function_ref<bool(ArrayRef<QualType>)> CheckNonDependent) {}

QualType Sema::adjustCCAndNoReturn(QualType ArgFunctionType,
                                   QualType FunctionType,
                                   bool AdjustExceptionSpec) {}

TemplateDeductionResult Sema::DeduceTemplateArguments(
    FunctionTemplateDecl *FunctionTemplate,
    TemplateArgumentListInfo *ExplicitTemplateArgs, QualType ArgFunctionType,
    FunctionDecl *&Specialization, TemplateDeductionInfo &Info,
    bool IsAddressOfFunction) {}

TemplateDeductionResult Sema::DeduceTemplateArguments(
    FunctionTemplateDecl *ConversionTemplate, QualType ObjectType,
    Expr::Classification ObjectClassification, QualType A,
    CXXConversionDecl *&Specialization, TemplateDeductionInfo &Info) {}

TemplateDeductionResult
Sema::DeduceTemplateArguments(FunctionTemplateDecl *FunctionTemplate,
                              TemplateArgumentListInfo *ExplicitTemplateArgs,
                              FunctionDecl *&Specialization,
                              TemplateDeductionInfo &Info,
                              bool IsAddressOfFunction) {}

namespace {
  struct DependentAuto {};

  /// Substitute the 'auto' specifier or deduced template specialization type
  /// specifier within a type for a given replacement type.
  class SubstituteDeducedTypeTransform :
      public TreeTransform<SubstituteDeducedTypeTransform> {};

} // namespace

static bool CheckDeducedPlaceholderConstraints(Sema &S, const AutoType &Type,
                                               AutoTypeLoc TypeLoc,
                                               QualType Deduced) {}

TemplateDeductionResult
Sema::DeduceAutoType(TypeLoc Type, Expr *Init, QualType &Result,
                     TemplateDeductionInfo &Info, bool DependentDeduction,
                     bool IgnoreConstraints,
                     TemplateSpecCandidateSet *FailedTSC) {}

QualType Sema::SubstAutoType(QualType TypeWithAuto,
                             QualType TypeToReplaceAuto) {}

TypeSourceInfo *Sema::SubstAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                              QualType TypeToReplaceAuto) {}

QualType Sema::SubstAutoTypeDependent(QualType TypeWithAuto) {}

TypeSourceInfo *
Sema::SubstAutoTypeSourceInfoDependent(TypeSourceInfo *TypeWithAuto) {}

QualType Sema::ReplaceAutoType(QualType TypeWithAuto,
                               QualType TypeToReplaceAuto) {}

TypeSourceInfo *Sema::ReplaceAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                                QualType TypeToReplaceAuto) {}

void Sema::DiagnoseAutoDeductionFailure(const VarDecl *VDecl,
                                        const Expr *Init) {}

bool Sema::DeduceReturnType(FunctionDecl *FD, SourceLocation Loc,
                            bool Diagnose) {}

bool Sema::CheckIfFunctionSpecializationIsImmediate(FunctionDecl *FD,
                                                    SourceLocation Loc) {}

static QualType GetImplicitObjectParameterType(ASTContext &Context,
                                               const CXXMethodDecl *Method,
                                               QualType RawType,
                                               bool IsOtherRvr) {}

static TemplateDeductionResult CheckDeductionConsistency(
    Sema &S, FunctionTemplateDecl *FTD, int ArgIdx, QualType P, QualType A,
    ArrayRef<TemplateArgument> DeducedArgs, bool CheckConsistency) {}

template <class T>
static TemplateDeductionResult FinishTemplateArgumentDeduction(
    Sema &S, FunctionTemplateDecl *FTD,
    SmallVectorImpl<DeducedTemplateArgument> &Deduced,
    TemplateDeductionInfo &Info, T &&CheckDeductionConsistency) {}

/// Determine whether the function template \p FT1 is at least as
/// specialized as \p FT2.
static bool isAtLeastAsSpecializedAs(
    Sema &S, SourceLocation Loc, FunctionTemplateDecl *FT1,
    FunctionTemplateDecl *FT2, TemplatePartialOrderingContext TPOC,
    ArrayRef<QualType> Args1, ArrayRef<QualType> Args2, bool Args1Offset) {}

FunctionTemplateDecl *Sema::getMoreSpecializedTemplate(
    FunctionTemplateDecl *FT1, FunctionTemplateDecl *FT2, SourceLocation Loc,
    TemplatePartialOrderingContext TPOC, unsigned NumCallArguments1,
    QualType RawObj1Ty, QualType RawObj2Ty, bool Reversed) {}

UnresolvedSetIterator Sema::getMostSpecialized(
    UnresolvedSetIterator SpecBegin, UnresolvedSetIterator SpecEnd,
    TemplateSpecCandidateSet &FailedCandidates,
    SourceLocation Loc, const PartialDiagnostic &NoneDiag,
    const PartialDiagnostic &AmbigDiag, const PartialDiagnostic &CandidateDiag,
    bool Complain, QualType TargetType) {}

FunctionDecl *Sema::getMoreConstrainedFunction(FunctionDecl *FD1,
                                               FunctionDecl *FD2) {}

/// Determine whether one partial specialization, P1, is at least as
/// specialized than another, P2.
///
/// \tparam TemplateLikeDecl The kind of P2, which must be a
/// TemplateDecl or {Class,Var}TemplatePartialSpecializationDecl.
/// \param T1 The injected-class-name of P1 (faked for a variable template).
/// \param T2 The injected-class-name of P2 (faked for a variable template).
template<typename TemplateLikeDecl>
static bool isAtLeastAsSpecializedAs(Sema &S, QualType T1, QualType T2,
                                     TemplateLikeDecl *P2,
                                     TemplateDeductionInfo &Info) {}

namespace {
// A dummy class to return nullptr instead of P2 when performing "more
// specialized than primary" check.
struct GetP2 {};

// The assumption is that two template argument lists have the same size.
struct TemplateArgumentListAreEqual {};
} // namespace

/// Returns the more specialized template specialization between T1/P1 and
/// T2/P2.
/// - If IsMoreSpecialThanPrimaryCheck is true, T1/P1 is the partial
///   specialization and T2/P2 is the primary template.
/// - otherwise, both T1/P1 and T2/P2 are the partial specialization.
///
/// \param T1 the type of the first template partial specialization
///
/// \param T2 if IsMoreSpecialThanPrimaryCheck is true, the type of the second
///           template partial specialization; otherwise, the type of the
///           primary template.
///
/// \param P1 the first template partial specialization
///
/// \param P2 if IsMoreSpecialThanPrimaryCheck is true, the second template
///           partial specialization; otherwise, the primary template.
///
/// \returns - If IsMoreSpecialThanPrimaryCheck is true, returns P1 if P1 is
///            more specialized, returns nullptr if P1 is not more specialized.
///          - otherwise, returns the more specialized template partial
///            specialization. If neither partial specialization is more
///            specialized, returns NULL.
template <typename TemplateLikeDecl, typename PrimaryDel>
static TemplateLikeDecl *
getMoreSpecialized(Sema &S, QualType T1, QualType T2, TemplateLikeDecl *P1,
                   PrimaryDel *P2, TemplateDeductionInfo &Info) {}

ClassTemplatePartialSpecializationDecl *
Sema::getMoreSpecializedPartialSpecialization(
                                  ClassTemplatePartialSpecializationDecl *PS1,
                                  ClassTemplatePartialSpecializationDecl *PS2,
                                              SourceLocation Loc) {}

bool Sema::isMoreSpecializedThanPrimary(
    ClassTemplatePartialSpecializationDecl *Spec, TemplateDeductionInfo &Info) {}

VarTemplatePartialSpecializationDecl *
Sema::getMoreSpecializedPartialSpecialization(
    VarTemplatePartialSpecializationDecl *PS1,
    VarTemplatePartialSpecializationDecl *PS2, SourceLocation Loc) {}

bool Sema::isMoreSpecializedThanPrimary(
    VarTemplatePartialSpecializationDecl *Spec, TemplateDeductionInfo &Info) {}

bool Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs(
    TemplateParameterList *P, TemplateDecl *AArg,
    const DefaultArguments &DefaultArgs, SourceLocation Loc, bool IsDeduced) {}

namespace {
struct MarkUsedTemplateParameterVisitor :
    RecursiveASTVisitor<MarkUsedTemplateParameterVisitor> {};
}

/// Mark the template parameters that are used by the given
/// expression.
static void
MarkUsedTemplateParameters(ASTContext &Ctx,
                           const Expr *E,
                           bool OnlyDeduced,
                           unsigned Depth,
                           llvm::SmallBitVector &Used) {}

/// Mark the template parameters that are used by the given
/// nested name specifier.
static void
MarkUsedTemplateParameters(ASTContext &Ctx,
                           NestedNameSpecifier *NNS,
                           bool OnlyDeduced,
                           unsigned Depth,
                           llvm::SmallBitVector &Used) {}

/// Mark the template parameters that are used by the given
/// template name.
static void
MarkUsedTemplateParameters(ASTContext &Ctx,
                           TemplateName Name,
                           bool OnlyDeduced,
                           unsigned Depth,
                           llvm::SmallBitVector &Used) {}

/// Mark the template parameters that are used by the given
/// type.
static void
MarkUsedTemplateParameters(ASTContext &Ctx, QualType T,
                           bool OnlyDeduced,
                           unsigned Depth,
                           llvm::SmallBitVector &Used) {}

/// Mark the template parameters that are used by this
/// template argument.
static void
MarkUsedTemplateParameters(ASTContext &Ctx,
                           const TemplateArgument &TemplateArg,
                           bool OnlyDeduced,
                           unsigned Depth,
                           llvm::SmallBitVector &Used) {}

void
Sema::MarkUsedTemplateParameters(const Expr *E, bool OnlyDeduced,
                                 unsigned Depth,
                                 llvm::SmallBitVector &Used) {}

void
Sema::MarkUsedTemplateParameters(const TemplateArgumentList &TemplateArgs,
                                 bool OnlyDeduced, unsigned Depth,
                                 llvm::SmallBitVector &Used) {}

void Sema::MarkDeducedTemplateParameters(
    ASTContext &Ctx, const FunctionTemplateDecl *FunctionTemplate,
    llvm::SmallBitVector &Deduced) {}

bool hasDeducibleTemplateParameters(Sema &S,
                                    FunctionTemplateDecl *FunctionTemplate,
                                    QualType T) {}