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//===------- SemaTemplate.cpp - Semantic Analysis for C++ Templates -------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements semantic analysis for C++ templates.
#include "TreeTransform.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclFriend.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/TypeVisitor.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Basic/Stack.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/ParsedTemplate.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/Template.h"
#include "clang/Sema/TemplateDeduction.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
#include <iterator>
using namespace clang;
using namespace sema;
// Exported for use by Parser.
clang::getTemplateParamsRange(TemplateParameterList const * const *Ps,
unsigned N) {
if (!N) return SourceRange();
return SourceRange(Ps[0]->getTemplateLoc(), Ps[N-1]->getRAngleLoc());
namespace clang {
/// [temp.constr.decl]p2: A template's associated constraints are
/// defined as a single constraint-expression derived from the introduced
/// constraint-expressions [ ... ].
/// \param Params The template parameter list and optional requires-clause.
/// \param FD The underlying templated function declaration for a function
/// template.
static Expr *formAssociatedConstraints(TemplateParameterList *Params,
FunctionDecl *FD);
static Expr *clang::formAssociatedConstraints(TemplateParameterList *Params,
FunctionDecl *FD) {
// FIXME: Concepts: collect additional introduced constraint-expressions
assert(!FD && "Cannot collect constraints from function declaration yet.");
return Params->getRequiresClause();
/// Determine whether the declaration found is acceptable as the name
/// of a template and, if so, return that template declaration. Otherwise,
/// returns null.
/// Note that this may return an UnresolvedUsingValueDecl if AllowDependent
/// is true. In all other cases it will return a TemplateDecl (or null).
NamedDecl *Sema::getAsTemplateNameDecl(NamedDecl *D,
bool AllowFunctionTemplates,
bool AllowDependent) {
D = D->getUnderlyingDecl();
if (isa<TemplateDecl>(D)) {
if (!AllowFunctionTemplates && isa<FunctionTemplateDecl>(D))
return nullptr;
return D;
if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
// C++ [temp.local]p1:
// Like normal (non-template) classes, class templates have an
// injected-class-name (Clause 9). The injected-class-name
// can be used with or without a template-argument-list. When
// it is used without a template-argument-list, it is
// equivalent to the injected-class-name followed by the
// template-parameters of the class template enclosed in
// <>. When it is used with a template-argument-list, it
// refers to the specified class template specialization,
// which could be the current specialization or another
// specialization.
if (Record->isInjectedClassName()) {
Record = cast<CXXRecordDecl>(Record->getDeclContext());
if (Record->getDescribedClassTemplate())
return Record->getDescribedClassTemplate();
if (ClassTemplateSpecializationDecl *Spec
= dyn_cast<ClassTemplateSpecializationDecl>(Record))
return Spec->getSpecializedTemplate();
return nullptr;
// 'using Dependent::foo;' can resolve to a template name.
// 'using typename Dependent::foo;' cannot (not even if 'foo' is an
// injected-class-name).
if (AllowDependent && isa<UnresolvedUsingValueDecl>(D))
return D;
return nullptr;
void Sema::FilterAcceptableTemplateNames(LookupResult &R,
bool AllowFunctionTemplates,
bool AllowDependent) {
LookupResult::Filter filter = R.makeFilter();
while (filter.hasNext()) {
NamedDecl *Orig =;
if (!getAsTemplateNameDecl(Orig, AllowFunctionTemplates, AllowDependent))
bool Sema::hasAnyAcceptableTemplateNames(LookupResult &R,
bool AllowFunctionTemplates,
bool AllowDependent,
bool AllowNonTemplateFunctions) {
for (LookupResult::iterator I = R.begin(), IEnd = R.end(); I != IEnd; ++I) {
if (getAsTemplateNameDecl(*I, AllowFunctionTemplates, AllowDependent))
return true;
if (AllowNonTemplateFunctions &&
return true;
return false;
TemplateNameKind Sema::isTemplateName(Scope *S,
CXXScopeSpec &SS,
bool hasTemplateKeyword,
const UnqualifiedId &Name,
ParsedType ObjectTypePtr,
bool EnteringContext,
TemplateTy &TemplateResult,
bool &MemberOfUnknownSpecialization) {
assert(getLangOpts().CPlusPlus && "No template names in C!");
DeclarationName TName;
MemberOfUnknownSpecialization = false;
switch (Name.getKind()) {
case UnqualifiedIdKind::IK_Identifier:
TName = DeclarationName(Name.Identifier);
case UnqualifiedIdKind::IK_OperatorFunctionId:
TName = Context.DeclarationNames.getCXXOperatorName(
case UnqualifiedIdKind::IK_LiteralOperatorId:
TName = Context.DeclarationNames.getCXXLiteralOperatorName(Name.Identifier);
return TNK_Non_template;
QualType ObjectType = ObjectTypePtr.get();
AssumedTemplateKind AssumedTemplate;
LookupResult R(*this, TName, Name.getBeginLoc(), LookupOrdinaryName);
if (LookupTemplateName(R, S, SS, ObjectType, EnteringContext,
MemberOfUnknownSpecialization, SourceLocation(),
return TNK_Non_template;
if (AssumedTemplate != AssumedTemplateKind::None) {
TemplateResult = TemplateTy::make(Context.getAssumedTemplateName(TName));
// Let the parser know whether we found nothing or found functions; if we
// found nothing, we want to more carefully check whether this is actually
// a function template name versus some other kind of undeclared identifier.
return AssumedTemplate == AssumedTemplateKind::FoundNothing
? TNK_Undeclared_template
: TNK_Function_template;
if (R.empty())
return TNK_Non_template;
NamedDecl *D = nullptr;
if (R.isAmbiguous()) {
// If we got an ambiguity involving a non-function template, treat this
// as a template name, and pick an arbitrary template for error recovery.
bool AnyFunctionTemplates = false;
for (NamedDecl *FoundD : R) {
if (NamedDecl *FoundTemplate = getAsTemplateNameDecl(FoundD)) {
if (isa<FunctionTemplateDecl>(FoundTemplate))
AnyFunctionTemplates = true;
else {
D = FoundTemplate;
// If we didn't find any templates at all, this isn't a template name.
// Leave the ambiguity for a later lookup to diagnose.
if (!D && !AnyFunctionTemplates) {
return TNK_Non_template;
// If the only templates were function templates, filter out the rest.
// We'll diagnose the ambiguity later.
if (!D)
// At this point, we have either picked a single template name declaration D
// or we have a non-empty set of results R containing either one template name
// declaration or a set of function templates.
TemplateName Template;
TemplateNameKind TemplateKind;
unsigned ResultCount = R.end() - R.begin();
if (!D && ResultCount > 1) {
// We assume that we'll preserve the qualifier from a function
// template name in other ways.
Template = Context.getOverloadedTemplateName(R.begin(), R.end());
TemplateKind = TNK_Function_template;
// We'll do this lookup again later.
} else {
if (!D) {
D = getAsTemplateNameDecl(*R.begin());
assert(D && "unambiguous result is not a template name");
if (isa<UnresolvedUsingValueDecl>(D)) {
// We don't yet know whether this is a template-name or not.
MemberOfUnknownSpecialization = true;
return TNK_Non_template;
TemplateDecl *TD = cast<TemplateDecl>(D);
if (SS.isSet() && !SS.isInvalid()) {
NestedNameSpecifier *Qualifier = SS.getScopeRep();
Template = Context.getQualifiedTemplateName(Qualifier,
hasTemplateKeyword, TD);
} else {
Template = TemplateName(TD);
if (isa<FunctionTemplateDecl>(TD)) {
TemplateKind = TNK_Function_template;
// We'll do this lookup again later.
} else {
assert(isa<ClassTemplateDecl>(TD) || isa<TemplateTemplateParmDecl>(TD) ||
isa<TypeAliasTemplateDecl>(TD) || isa<VarTemplateDecl>(TD) ||
isa<BuiltinTemplateDecl>(TD) || isa<ConceptDecl>(TD));
TemplateKind =
isa<VarTemplateDecl>(TD) ? TNK_Var_template :
isa<ConceptDecl>(TD) ? TNK_Concept_template :
TemplateResult = TemplateTy::make(Template);
return TemplateKind;
bool Sema::isDeductionGuideName(Scope *S, const IdentifierInfo &Name,
SourceLocation NameLoc,
ParsedTemplateTy *Template) {
CXXScopeSpec SS;
bool MemberOfUnknownSpecialization = false;
// We could use redeclaration lookup here, but we don't need to: the
// syntactic form of a deduction guide is enough to identify it even
// if we can't look up the template name at all.
LookupResult R(*this, DeclarationName(&Name), NameLoc, LookupOrdinaryName);
if (LookupTemplateName(R, S, SS, /*ObjectType*/ QualType(),
/*EnteringContext*/ false,
return false;
if (R.empty()) return false;
if (R.isAmbiguous()) {
// FIXME: Diagnose an ambiguity if we find at least one template.
return false;
// We only treat template-names that name type templates as valid deduction
// guide names.
TemplateDecl *TD = R.getAsSingle<TemplateDecl>();
if (!TD || !getAsTypeTemplateDecl(TD))
return false;
if (Template)
*Template = TemplateTy::make(TemplateName(TD));
return true;
bool Sema::DiagnoseUnknownTemplateName(const IdentifierInfo &II,
SourceLocation IILoc,
Scope *S,
const CXXScopeSpec *SS,
TemplateTy &SuggestedTemplate,
TemplateNameKind &SuggestedKind) {
// We can't recover unless there's a dependent scope specifier preceding the
// template name.
// FIXME: Typo correction?
if (!SS || !SS->isSet() || !isDependentScopeSpecifier(*SS) ||
return false;
// The code is missing a 'template' keyword prior to the dependent template
// name.
NestedNameSpecifier *Qualifier = (NestedNameSpecifier*)SS->getScopeRep();
Diag(IILoc, diag::err_template_kw_missing)
<< Qualifier << II.getName()
<< FixItHint::CreateInsertion(IILoc, "template ");
= TemplateTy::make(Context.getDependentTemplateName(Qualifier, &II));
SuggestedKind = TNK_Dependent_template_name;
return true;
bool Sema::LookupTemplateName(LookupResult &Found,
Scope *S, CXXScopeSpec &SS,
QualType ObjectType,
bool EnteringContext,
bool &MemberOfUnknownSpecialization,
SourceLocation TemplateKWLoc,
AssumedTemplateKind *ATK) {
if (ATK)
*ATK = AssumedTemplateKind::None;
// Determine where to perform name lookup
MemberOfUnknownSpecialization = false;
DeclContext *LookupCtx = nullptr;
bool IsDependent = false;
if (!ObjectType.isNull()) {
// This nested-name-specifier occurs in a member access expression, e.g.,
// x->B::f, and we are looking into the type of the object.
assert(!SS.isSet() && "ObjectType and scope specifier cannot coexist");
LookupCtx = computeDeclContext(ObjectType);
IsDependent = !LookupCtx && ObjectType->isDependentType();
assert((IsDependent || !ObjectType->isIncompleteType() ||
ObjectType->castAs<TagType>()->isBeingDefined()) &&
"Caller should have completed object type");
// Template names cannot appear inside an Objective-C class or object type
// or a vector type.
// FIXME: This is wrong. For example:
// template<typename T> using Vec = T __attribute__((ext_vector_type(4)));
// Vec<int> vi;
// vi.Vec<int>::~Vec<int>();
// ... should be accepted but we will not treat 'Vec' as a template name
// here. The right thing to do would be to check if the name is a valid
// vector component name, and look up a template name if not. And similarly
// for lookups into Objective-C class and object types, where the same
// problem can arise.
if (ObjectType->isObjCObjectOrInterfaceType() ||
ObjectType->isVectorType()) {
return false;
} else if (SS.isSet()) {
// This nested-name-specifier occurs after another nested-name-specifier,
// so long into the context associated with the prior nested-name-specifier.
LookupCtx = computeDeclContext(SS, EnteringContext);
IsDependent = !LookupCtx;
// The declaration context must be complete.
if (LookupCtx && RequireCompleteDeclContext(SS, LookupCtx))
return true;
bool ObjectTypeSearchedInScope = false;
bool AllowFunctionTemplatesInLookup = true;
if (LookupCtx) {
// Perform "qualified" name lookup into the declaration context we
// computed, which is either the type of the base of a member access
// expression or the declaration context associated with a prior
// nested-name-specifier.
LookupQualifiedName(Found, LookupCtx);
// FIXME: The C++ standard does not clearly specify what happens in the
// case where the object type is dependent, and implementations vary. In
// Clang, we treat a name after a . or -> as a template-name if lookup
// finds a non-dependent member or member of the current instantiation that
// is a type template, or finds no such members and lookup in the context
// of the postfix-expression finds a type template. In the latter case, the
// name is nonetheless dependent, and we may resolve it to a member of an
// unknown specialization when we come to instantiate the template.
IsDependent |= Found.wasNotFoundInCurrentInstantiation();
if (!SS.isSet() && (ObjectType.isNull() || Found.empty())) {
// C++ [basic.lookup.classref]p1:
// In a class member access expression (5.2.5), if the . or -> token is
// immediately followed by an identifier followed by a <, the
// identifier must be looked up to determine whether the < is the
// beginning of a template argument list (14.2) or a less-than operator.
// The identifier is first looked up in the class of the object
// expression. If the identifier is not found, it is then looked up in
// the context of the entire postfix-expression and shall name a class
// template.
if (S)
LookupName(Found, S);
if (!ObjectType.isNull()) {
// FIXME: We should filter out all non-type templates here, particularly
// variable templates and concepts. But the exclusion of alias templates
// and template template parameters is a wording defect.
AllowFunctionTemplatesInLookup = false;
ObjectTypeSearchedInScope = true;
IsDependent |= Found.wasNotFoundInCurrentInstantiation();
if (Found.isAmbiguous())
return false;
if (ATK && !SS.isSet() && ObjectType.isNull() && TemplateKWLoc.isInvalid()) {
// C++2a [temp.names]p2:
// A name is also considered to refer to a template if it is an
// unqualified-id followed by a < and name lookup finds either one or more
// functions or finds nothing.
// To keep our behavior consistent, we apply the "finds nothing" part in
// all language modes, and diagnose the empty lookup in ActOnCallExpr if we
// successfully form a call to an undeclared template-id.
bool AllFunctions =
getLangOpts().CPlusPlus2a &&
std::all_of(Found.begin(), Found.end(), [](NamedDecl *ND) {
return isa<FunctionDecl>(ND->getUnderlyingDecl());
if (AllFunctions || (Found.empty() && !IsDependent)) {
// If lookup found any functions, or if this is a name that can only be
// used for a function, then strongly assume this is a function
// template-id.
*ATK = (Found.empty() && Found.getLookupName().isIdentifier())
? AssumedTemplateKind::FoundNothing
: AssumedTemplateKind::FoundFunctions;
return false;
if (Found.empty() && !IsDependent) {
// If we did not find any names, attempt to correct any typos.
DeclarationName Name = Found.getLookupName();
// Simple filter callback that, for keywords, only accepts the C++ *_cast
DefaultFilterCCC FilterCCC{};
FilterCCC.WantTypeSpecifiers = false;
FilterCCC.WantExpressionKeywords = false;
FilterCCC.WantRemainingKeywords = false;
FilterCCC.WantCXXNamedCasts = true;
if (TypoCorrection Corrected =
CorrectTypo(Found.getLookupNameInfo(), Found.getLookupKind(), S,
&SS, FilterCCC, CTK_ErrorRecovery, LookupCtx)) {
if (auto *ND = Corrected.getFoundDecl())
if (Found.isAmbiguous()) {
} else if (!Found.empty()) {
if (LookupCtx) {
std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
Name.getAsString() == CorrectedStr;
diagnoseTypo(Corrected, PDiag(diag::err_no_member_template_suggest)
<< Name << LookupCtx << DroppedSpecifier
<< SS.getRange());
} else {
diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest) << Name);
NamedDecl *ExampleLookupResult =
Found.empty() ? nullptr : Found.getRepresentativeDecl();
FilterAcceptableTemplateNames(Found, AllowFunctionTemplatesInLookup);
if (Found.empty()) {
if (IsDependent) {
MemberOfUnknownSpecialization = true;
return false;
// If a 'template' keyword was used, a lookup that finds only non-template
// names is an error.
if (ExampleLookupResult && TemplateKWLoc.isValid()) {
Diag(Found.getNameLoc(), diag::err_template_kw_refers_to_non_template)
<< Found.getLookupName() << SS.getRange();
<< Found.getLookupName();
return true;
return false;
if (S && !ObjectType.isNull() && !ObjectTypeSearchedInScope &&
!getLangOpts().CPlusPlus11) {
// C++03 [basic.lookup.classref]p1:
// [...] If the lookup in the class of the object expression finds a
// template, the name is also looked up in the context of the entire
// postfix-expression and [...]
// Note: C++11 does not perform this second lookup.
LookupResult FoundOuter(*this, Found.getLookupName(), Found.getNameLoc(),
LookupName(FoundOuter, S);
// FIXME: We silently accept an ambiguous lookup here, in violation of
// [basic.lookup]/1.
FilterAcceptableTemplateNames(FoundOuter, /*AllowFunctionTemplates=*/false);
NamedDecl *OuterTemplate;
if (FoundOuter.empty()) {
// - if the name is not found, the name found in the class of the
// object expression is used, otherwise
} else if (FoundOuter.isAmbiguous() || !FoundOuter.isSingleResult() ||
!(OuterTemplate =
getAsTemplateNameDecl(FoundOuter.getFoundDecl()))) {
// - if the name is found in the context of the entire
// postfix-expression and does not name a class template, the name
// found in the class of the object expression is used, otherwise
} else if (!Found.isSuppressingDiagnostics()) {
// - if the name found is a class template, it must refer to the same
// entity as the one found in the class of the object expression,
// otherwise the program is ill-formed.
if (!Found.isSingleResult() ||
getAsTemplateNameDecl(Found.getFoundDecl())->getCanonicalDecl() !=
OuterTemplate->getCanonicalDecl()) {
<< Found.getLookupName()
<< ObjectType;
<< ObjectType;
// Recover by taking the template that we found in the object
// expression's type.
return false;
void Sema::diagnoseExprIntendedAsTemplateName(Scope *S, ExprResult TemplateName,
SourceLocation Less,
SourceLocation Greater) {
if (TemplateName.isInvalid())
DeclarationNameInfo NameInfo;
CXXScopeSpec SS;
LookupNameKind LookupKind;
DeclContext *LookupCtx = nullptr;
NamedDecl *Found = nullptr;
bool MissingTemplateKeyword = false;
// Figure out what name we looked up.
if (auto *DRE = dyn_cast<DeclRefExpr>(TemplateName.get())) {
NameInfo = DRE->getNameInfo();
LookupKind = LookupOrdinaryName;
Found = DRE->getFoundDecl();
} else if (auto *ME = dyn_cast<MemberExpr>(TemplateName.get())) {
NameInfo = ME->getMemberNameInfo();
LookupKind = LookupMemberName;
LookupCtx = ME->getBase()->getType()->getAsCXXRecordDecl();
Found = ME->getMemberDecl();
} else if (auto *DSDRE =
dyn_cast<DependentScopeDeclRefExpr>(TemplateName.get())) {
NameInfo = DSDRE->getNameInfo();
MissingTemplateKeyword = true;
} else if (auto *DSME =
dyn_cast<CXXDependentScopeMemberExpr>(TemplateName.get())) {
NameInfo = DSME->getMemberNameInfo();
MissingTemplateKeyword = true;
} else {
llvm_unreachable("unexpected kind of potential template name");
// If this is a dependent-scope lookup, diagnose that the 'template' keyword
// was missing.
if (MissingTemplateKeyword) {
Diag(NameInfo.getBeginLoc(), diag::err_template_kw_missing)
<< "" << NameInfo.getName().getAsString() << SourceRange(Less, Greater);
// Try to correct the name by looking for templates and C++ named casts.
struct TemplateCandidateFilter : CorrectionCandidateCallback {
Sema &S;
TemplateCandidateFilter(Sema &S) : S(S) {
WantTypeSpecifiers = false;
WantExpressionKeywords = false;
WantRemainingKeywords = false;
WantCXXNamedCasts = true;
bool ValidateCandidate(const TypoCorrection &Candidate) override {
if (auto *ND = Candidate.getCorrectionDecl())
return S.getAsTemplateNameDecl(ND);
return Candidate.isKeyword();
std::unique_ptr<CorrectionCandidateCallback> clone() override {
return std::make_unique<TemplateCandidateFilter>(*this);
DeclarationName Name = NameInfo.getName();
TemplateCandidateFilter CCC(*this);
if (TypoCorrection Corrected = CorrectTypo(NameInfo, LookupKind, S, &SS, CCC,
CTK_ErrorRecovery, LookupCtx)) {
auto *ND = Corrected.getFoundDecl();
if (ND)
ND = getAsTemplateNameDecl(ND);
if (ND || Corrected.isKeyword()) {
if (LookupCtx) {
std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
Name.getAsString() == CorrectedStr;
<< Name << LookupCtx << DroppedSpecifier
<< SS.getRange(), false);
} else {
<< Name, false);
if (Found)
Diag(NameInfo.getLoc(), diag::err_non_template_in_template_id)
<< Name << SourceRange(Less, Greater);
if (Found)
Diag(Found->getLocation(), diag::note_non_template_in_template_id_found);
/// ActOnDependentIdExpression - Handle a dependent id-expression that
/// was just parsed. This is only possible with an explicit scope
/// specifier naming a dependent type.
Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
SourceLocation TemplateKWLoc,
const DeclarationNameInfo &NameInfo,
bool isAddressOfOperand,
const TemplateArgumentListInfo *TemplateArgs) {
DeclContext *DC = getFunctionLevelDeclContext();
// C++11 [expr.prim.general]p12:
// An id-expression that denotes a non-static data member or non-static
// member function of a class can only be used:
// (...)
// - if that id-expression denotes a non-static data member and it
// appears in an unevaluated operand.
// If this might be the case, form a DependentScopeDeclRefExpr instead of a
// CXXDependentScopeMemberExpr. The former can instantiate to either
// DeclRefExpr or MemberExpr depending on lookup results, while the latter is
// always a MemberExpr.
bool MightBeCxx11UnevalField =
getLangOpts().CPlusPlus11 && isUnevaluatedContext();
// Check if the nested name specifier is an enum type.
bool IsEnum = false;
if (NestedNameSpecifier *NNS = SS.getScopeRep())
IsEnum = dyn_cast_or_null<EnumType>(NNS->getAsType());
if (!MightBeCxx11UnevalField && !isAddressOfOperand && !IsEnum &&
isa<CXXMethodDecl>(DC) && cast<CXXMethodDecl>(DC)->isInstance()) {
QualType ThisType = cast<CXXMethodDecl>(DC)->getThisType();
// Since the 'this' expression is synthesized, we don't need to
// perform the double-lookup check.
NamedDecl *FirstQualifierInScope = nullptr;
return CXXDependentScopeMemberExpr::Create(
Context, /*This*/ nullptr, ThisType, /*IsArrow*/ true,
/*Op*/ SourceLocation(), SS.getWithLocInContext(Context), TemplateKWLoc,
FirstQualifierInScope, NameInfo, TemplateArgs);
return BuildDependentDeclRefExpr(SS, TemplateKWLoc, NameInfo, TemplateArgs);
Sema::BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
SourceLocation TemplateKWLoc,
const DeclarationNameInfo &NameInfo,
const TemplateArgumentListInfo *TemplateArgs) {
// DependentScopeDeclRefExpr::Create requires a valid QualifierLoc
NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
if (!QualifierLoc)
return ExprError();
return DependentScopeDeclRefExpr::Create(
Context, QualifierLoc, TemplateKWLoc, NameInfo, TemplateArgs);
/// Determine whether we would be unable to instantiate this template (because
/// it either has no definition, or is in the process of being instantiated).
bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
NamedDecl *Instantiation,
bool InstantiatedFromMember,
const NamedDecl *Pattern,
const NamedDecl *PatternDef,
TemplateSpecializationKind TSK,
bool Complain /*= true*/) {
assert(isa<TagDecl>(Instantiation) || isa<FunctionDecl>(Instantiation) ||
bool IsEntityBeingDefined = false;
if (const TagDecl *TD = dyn_cast_or_null<TagDecl>(PatternDef))
IsEntityBeingDefined = TD->isBeingDefined();
if (PatternDef && !IsEntityBeingDefined) {
NamedDecl *SuggestedDef = nullptr;
if (!hasVisibleDefinition(const_cast<NamedDecl*>(PatternDef), &SuggestedDef,
/*OnlyNeedComplete*/false)) {
// If we're allowed to diagnose this and recover, do so.
bool Recover = Complain && !isSFINAEContext();
if (Complain)
diagnoseMissingImport(PointOfInstantiation, SuggestedDef,
Sema::MissingImportKind::Definition, Recover);
return !Recover;
return false;
if (!Complain || (PatternDef && PatternDef->isInvalidDecl()))
return true;
llvm::Optional<unsigned> Note;
QualType InstantiationTy;
if (TagDecl *TD = dyn_cast<TagDecl>(Instantiation))
InstantiationTy = Context.getTypeDeclType(TD);
if (PatternDef) {
<< /*implicit|explicit*/(TSK != TSK_ImplicitInstantiation)
<< InstantiationTy;
// Not much point in noting the template declaration here, since
// we're lexically inside it.
} else if (InstantiatedFromMember) {
if (isa<FunctionDecl>(Instantiation)) {
<< /*member function*/ 1 << Instantiation->getDeclName()
<< Instantiation->getDeclContext();
Note = diag::note_explicit_instantiation_here;
} else {
assert(isa<TagDecl>(Instantiation) && "Must be a TagDecl!");
<< InstantiationTy;
Note = diag::note_member_declared_at;
} else {
if (isa<FunctionDecl>(Instantiation)) {
<< Pattern;
Note = diag::note_explicit_instantiation_here;
} else if (isa<TagDecl>(Instantiation)) {
Diag(PointOfInstantiation, diag::err_template_instantiate_undefined)
<< (TSK != TSK_ImplicitInstantiation)
<< InstantiationTy;
Note = diag::note_template_decl_here;
} else {
assert(isa<VarDecl>(Instantiation) && "Must be a VarDecl!");
if (isa<VarTemplateSpecializationDecl>(Instantiation)) {
<< Instantiation;
} else
<< /*static data member*/ 2 << Instantiation->getDeclName()
<< Instantiation->getDeclContext();
Note = diag::note_explicit_instantiation_here;
if (Note) // Diagnostics were emitted.
Diag(Pattern->getLocation(), Note.getValue());
// In general, Instantiation isn't marked invalid to get more than one
// error for multiple undefined instantiations. But the code that does
// explicit declaration -> explicit definition conversion can't handle
// invalid declarations, so mark as invalid in that case.
if (TSK == TSK_ExplicitInstantiationDeclaration)
return true;
/// DiagnoseTemplateParameterShadow - Produce a diagnostic complaining
/// that the template parameter 'PrevDecl' is being shadowed by a new
/// declaration at location Loc. Returns true to indicate that this is
/// an error, and false otherwise.
void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl) {
assert(PrevDecl->isTemplateParameter() && "Not a template parameter");
// C++ [temp.local]p4:
// A template-parameter shall not be redeclared within its
// scope (including nested scopes).
// Make this a warning when MSVC compatibility is requested.
unsigned DiagId = getLangOpts().MSVCCompat ? diag::ext_template_param_shadow
: diag::err_template_param_shadow;
Diag(Loc, DiagId) << cast<NamedDecl>(PrevDecl)->getDeclName();
Diag(PrevDecl->getLocation(), diag::note_template_param_here);
/// AdjustDeclIfTemplate - If the given decl happens to be a template, reset
/// the parameter D to reference the templated declaration and return a pointer
/// to the template declaration. Otherwise, do nothing to D and return null.
TemplateDecl *Sema::AdjustDeclIfTemplate(Decl *&D) {
if (TemplateDecl *Temp = dyn_cast_or_null<TemplateDecl>(D)) {
D = Temp->getTemplatedDecl();
return Temp;
return nullptr;
ParsedTemplateArgument ParsedTemplateArgument::getTemplatePackExpansion(
SourceLocation EllipsisLoc) const {
assert(Kind == Template &&
"Only template template arguments can be pack expansions here");
assert(getAsTemplate().get().containsUnexpandedParameterPack() &&
"Template template argument pack expansion without packs");
ParsedTemplateArgument Result(*this);
Result.EllipsisLoc = EllipsisLoc;
return Result;
static TemplateArgumentLoc translateTemplateArgument(Sema &SemaRef,
const ParsedTemplateArgument &Arg) {
switch (Arg.getKind()) {
case ParsedTemplateArgument::Type: {
TypeSourceInfo *DI;
QualType T = SemaRef.GetTypeFromParser(Arg.getAsType(), &DI);
if (!DI)
DI = SemaRef.Context.getTrivialTypeSourceInfo(T, Arg.getLocation());
return TemplateArgumentLoc(TemplateArgument(T), DI);
case ParsedTemplateArgument::NonType: {
Expr *E = static_cast<Expr *>(Arg.getAsExpr());
return TemplateArgumentLoc(TemplateArgument(E), E);
case ParsedTemplateArgument::Template: {
TemplateName Template = Arg.getAsTemplate().get();
TemplateArgument TArg;
if (Arg.getEllipsisLoc().isValid())
TArg = TemplateArgument(Template, Optional<unsigned int>());
TArg = Template;
return TemplateArgumentLoc(TArg,
llvm_unreachable("Unhandled parsed template argument");
/// Translates template arguments as provided by the parser
/// into template arguments used by semantic analysis.
void Sema::translateTemplateArguments(const ASTTemplateArgsPtr &TemplateArgsIn,
TemplateArgumentListInfo &TemplateArgs) {
for (unsigned I = 0, Last = TemplateArgsIn.size(); I != Last; ++I)
static void maybeDiagnoseTemplateParameterShadow(Sema &SemaRef, Scope *S,
SourceLocation Loc,
IdentifierInfo *Name) {
NamedDecl *PrevDecl = SemaRef.LookupSingleName(
S, Name, Loc, Sema::LookupOrdinaryName, Sema::ForVisibleRedeclaration);
if (PrevDecl && PrevDecl->isTemplateParameter())
SemaRef.DiagnoseTemplateParameterShadow(Loc, PrevDecl);
/// Convert a parsed type into a parsed template argument. This is mostly
/// trivial, except that we may have parsed a C++17 deduced class template
/// specialization type, in which case we should form a template template
/// argument instead of a type template argument.
ParsedTemplateArgument Sema::ActOnTemplateTypeArgument(TypeResult ParsedType) {
TypeSourceInfo *TInfo;
QualType T = GetTypeFromParser(ParsedType.get(), &TInfo);
if (T.isNull())
return ParsedTemplateArgument();
assert(TInfo && "template argument with no location");
// If we might have formed a deduced template specialization type, convert
// it to a template template argument.
if (getLangOpts().CPlusPlus17) {
TypeLoc TL = TInfo->getTypeLoc();
SourceLocation EllipsisLoc;
if (auto PET = TL.getAs<PackExpansionTypeLoc>()) {
EllipsisLoc = PET.getEllipsisLoc();
TL = PET.getPatternLoc();
CXXScopeSpec SS;
if (auto ET = TL.getAs<ElaboratedTypeLoc>()) {
TL = ET.getNamedTypeLoc();
if (auto DTST = TL.getAs<DeducedTemplateSpecializationTypeLoc>()) {
TemplateName Name = DTST.getTypePtr()->getTemplateName();
if (SS.isSet())
Name = Context.getQualifiedTemplateName(SS.getScopeRep(),
/*HasTemplateKeyword*/ false,
ParsedTemplateArgument Result(SS, TemplateTy::make(Name),
if (EllipsisLoc.isValid())
Result = Result.getTemplatePackExpansion(EllipsisLoc);
return Result;
// This is a normal type template argument. Note, if the type template
// argument is an injected-class-name for a template, it has a dual nature
// and can be used as either a type or a template. We handle that in
// convertTypeTemplateArgumentToTemplate.
return ParsedTemplateArgument(ParsedTemplateArgument::Type,
/// ActOnTypeParameter - Called when a C++ template type parameter
/// (e.g., "typename T") has been parsed. Typename specifies whether
/// the keyword "typename" was used to declare the type parameter
/// (otherwise, "class" was used), and KeyLoc is the location of the
/// "class" or "typename" keyword. ParamName is the name of the
/// parameter (NULL indicates an unnamed template parameter) and
/// ParamNameLoc is the location of the parameter name (if any).
/// If the type parameter has a default argument, it will be added
/// later via ActOnTypeParameterDefault.
NamedDecl *Sema::ActOnTypeParameter(Scope *S, bool Typename,
SourceLocation EllipsisLoc,
SourceLocation KeyLoc,
IdentifierInfo *ParamName,
SourceLocation ParamNameLoc,
unsigned Depth, unsigned Position,
SourceLocation EqualLoc,
ParsedType DefaultArg) {
assert(S->isTemplateParamScope() &&
"Template type parameter not in template parameter scope!");
bool IsParameterPack = EllipsisLoc.isValid();
TemplateTypeParmDecl *Param = TemplateTypeParmDecl::Create(
Context, Context.getTranslationUnitDecl(), KeyLoc, ParamNameLoc, Depth,
Position, ParamName, Typename, IsParameterPack);
if (Param->isParameterPack())
if (auto *LSI = getEnclosingLambda())
if (ParamName) {
maybeDiagnoseTemplateParameterShadow(*this, S, ParamNameLoc, ParamName);
// Add the template parameter into the current scope.
// C++0x [temp.param]p9:
// A default template-argument may be specified for any kind of
// template-parameter that is not a template parameter pack.
if (DefaultArg && IsParameterPack) {
Diag(EqualLoc, diag::err_template_param_pack_default_arg);
DefaultArg = nullptr;
// Handle the default argument, if provided.
if (DefaultArg) {
TypeSourceInfo *DefaultTInfo;
GetTypeFromParser(DefaultArg, &DefaultTInfo);
assert(DefaultTInfo && "expected source information for type");
// Check for unexpanded parameter packs.
if (DiagnoseUnexpandedParameterPack(ParamNameLoc, DefaultTInfo,
return Param;
// Check the template argument itself.
if (CheckTemplateArgument(Param, DefaultTInfo)) {
return Param;
return Param;
/// Check that the type of a non-type template parameter is
/// well-formed.
/// \returns the (possibly-promoted) parameter type if valid;
/// otherwise, produces a diagnostic and returns a NULL type.
QualType Sema::CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
SourceLocation Loc) {
if (TSI->getType()->isUndeducedType()) {
// C++17 [temp.dep.expr]p3:
// An id-expression is type-dependent if it contains
// - an identifier associated by name lookup with a non-type
// template-parameter declared with a type that contains a
// placeholder type (,
TSI = SubstAutoTypeSourceInfo(TSI, Context.DependentTy);
return CheckNonTypeTemplateParameterType(TSI->getType(), Loc);
QualType Sema::CheckNonTypeTemplateParameterType(QualType T,
SourceLocation Loc) {
// We don't allow variably-modified types as the type of non-type template
// parameters.
if (T->isVariablyModifiedType()) {
Diag(Loc, diag::err_variably_modified_nontype_template_param)
<< T;
return QualType();
// C++ [temp.param]p4:
// A non-type template-parameter shall have one of the following
// (optionally cv-qualified) types:
// -- integral or enumeration type,
if (T->isIntegralOrEnumerationType() ||
// -- pointer to object or pointer to function,
T->isPointerType() ||
// -- reference to object or reference to function,
T->isReferenceType() ||
// -- pointer to member,
T->isMemberPointerType() ||
// -- std::nullptr_t.
T->isNullPtrType() ||
// Allow use of auto in template parameter declarations.
T->isUndeducedType()) {
// C++ [temp.param]p5: The top-level cv-qualifiers on the template-parameter
// are ignored when determining its type.
return T.getUnqualifiedType();
// C++ [temp.param]p8:
// A non-type template-parameter of type "array of T" or
// "function returning T" is adjusted to be of type "pointer to
// T" or "pointer to function returning T", respectively.
if (T->isArrayType() || T->isFunctionType())
return Context.getDecayedType(T);
// If T is a dependent type, we can't do the check now, so we
// assume that it is well-formed. Note that stripping off the
// qualifiers here is not really correct if T turns out to be
// an array type, but we'll recompute the type everywhere it's
// used during instantiation, so that should be OK. (Using the
// qualified type is equally wrong.)
if (T->isDependentType())
return T.getUnqualifiedType();
Diag(Loc, diag::err_template_nontype_parm_bad_type)
<< T;
return QualType();
NamedDecl *Sema::ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
unsigned Depth,
unsigned Position,
SourceLocation EqualLoc,
Expr *Default) {
TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
// Check that we have valid decl-specifiers specified.
auto CheckValidDeclSpecifiers = [this, &D] {
// C++ [temp.param]
// p1
// template-parameter:
// ...
// parameter-declaration
// p2
// ... A storage class shall not be specified in a template-parameter
// declaration.
// [dcl.typedef]p1:
// The typedef specifier [...] shall not be used in the decl-specifier-seq
// of a parameter-declaration
const DeclSpec &DS = D.getDeclSpec();
auto EmitDiag = [this](SourceLocation Loc) {
Diag(Loc, diag::err_invalid_decl_specifier_in_nontype_parm)
<< FixItHint::CreateRemoval(Loc);
if (DS.getStorageClassSpec() != DeclSpec::SCS_unspecified)
if (DS.getThreadStorageClassSpec() != TSCS_unspecified)
// [dcl.inline]p1:
// The inline specifier can be applied only to the declaration or
// definition of a variable or function.
if (DS.isInlineSpecified())
// [dcl.constexpr]p1:
// The constexpr specifier shall be applied only to the definition of a
// variable or variable template or the declaration of a function or
// function template.
if (DS.hasConstexprSpecifier())
// [dcl.fct.spec]p1:
// Function-specifiers can be used only in function declarations.
if (DS.isVirtualSpecified())
if (DS.hasExplicitSpecifier())
if (DS.isNoreturnSpecified())
if (TInfo->getType()->isUndeducedType()) {
<< QualType(TInfo->getType()->getContainedAutoType(), 0);
assert(S->isTemplateParamScope() &&
"Non-type template parameter not in template parameter scope!");
bool Invalid = false;
QualType T = CheckNonTypeTemplateParameterType(TInfo, D.getIdentifierLoc());
if (T.isNull()) {
T = Context.IntTy; // Recover with an 'int' type.
Invalid = true;
CheckFunctionOrTemplateParamDeclarator(S, D);
IdentifierInfo *ParamName = D.getIdentifier();
bool IsParameterPack = D.hasEllipsis();
NonTypeTemplateParmDecl *Param = NonTypeTemplateParmDecl::Create(
Context, Context.getTranslationUnitDecl(), D.getBeginLoc(),
D.getIdentifierLoc(), Depth, Position, ParamName, T, IsParameterPack,
if (Invalid)
if (Param->isParameterPack())
if (auto *LSI = getEnclosingLambda())
if (ParamName) {
maybeDiagnoseTemplateParameterShadow(*this, S, D.getIdentifierLoc(),
// Add the template parameter into the current scope.
// C++0x [temp.param]p9:
// A default template-argument may be specified for any kind of
// template-parameter that is not a template parameter pack.
if (Default && IsParameterPack) {
Diag(EqualLoc, diag::err_template_param_pack_default_arg);
Default = nullptr;
// Check the well-formedness of the default template argument, if provided.
if (Default) {
// Check for unexpanded parameter packs.
if (DiagnoseUnexpandedParameterPack(Default, UPPC_DefaultArgument))
return Param;
TemplateArgument Converted;
ExprResult DefaultRes =
CheckTemplateArgument(Param, Param->getType(), Default, Converted);
if (DefaultRes.isInvalid()) {
return Param;
Default = DefaultRes.get();
return Param;
/// ActOnTemplateTemplateParameter - Called when a C++ template template
/// parameter (e.g. T in template <template \<typename> class T> class array)
/// has been parsed. S is the current scope.
NamedDecl *Sema::ActOnTemplateTemplateParameter(Scope* S,
SourceLocation TmpLoc,
TemplateParameterList *Params,
SourceLocation EllipsisLoc,
IdentifierInfo *Name,
SourceLocation NameLoc,
unsigned Depth,
unsigned Position,
SourceLocation EqualLoc,
ParsedTemplateArgument Default) {
assert(S->isTemplateParamScope() &&
"Template template parameter not in template parameter scope!");
// Construct the parameter object.
bool IsParameterPack = EllipsisLoc.isValid();
TemplateTemplateParmDecl *Param =
TemplateTemplateParmDecl::Create(Context, Context.getTranslationUnitDecl(),
NameLoc.isInvalid()? TmpLoc : NameLoc,
Depth, Position, IsParameterPack,
Name, Params);
if (Param->isParameterPack())
if (auto *LSI = getEnclosingLambda())
// If the template template parameter has a name, then link the identifier
// into the scope and lookup mechanisms.
if (Name) {
maybeDiagnoseTemplateParameterShadow(*this, S, NameLoc, Name);
if (Params->size() == 0) {
Diag(Param->getLocation(), diag::err_template_template_parm_no_parms)
<< SourceRange(Params->getLAngleLoc(), Params->getRAngleLoc());
// C++0x [temp.param]p9:
// A default template-argument may be specified for any kind of
// template-parameter that is not a template parameter pack.
if (IsParameterPack && !Default.isInvalid()) {
Diag(EqualLoc, diag::err_template_param_pack_default_arg);
Default = ParsedTemplateArgument();
if (!Default.isInvalid()) {
// Check only that we have a template template argument. We don't want to
// try to check well-formedness now, because our template template parameter
// might have dependent types in its template parameters, which we wouldn't
// be able to match now.
// If none of the template template parameter's template arguments mention
// other template parameters, we could actually perform more checking here.
// However, it isn't worth doing.
TemplateArgumentLoc DefaultArg = translateTemplateArgument(*this, Default);
if (DefaultArg.getArgument().getAsTemplate().isNull()) {
Diag(DefaultArg.getLocation(), diag::err_template_arg_not_valid_template)
<< DefaultArg.getSourceRange();
return Param;
// Check for unexpanded parameter packs.
if (DiagnoseUnexpandedParameterPack(DefaultArg.getLocation(),
return Param;
Param->setDefaultArgument(Context, DefaultArg);
return Param;
/// ActOnTemplateParameterList - Builds a TemplateParameterList, optionally
/// constrained by RequiresClause, that contains the template parameters in
/// Params.
TemplateParameterList *
Sema::ActOnTemplateParameterList(unsigned Depth,
SourceLocation ExportLoc,
SourceLocation TemplateLoc,
SourceLocation LAngleLoc,
ArrayRef<NamedDecl *> Params,
SourceLocation RAngleLoc,
Expr *RequiresClause) {
if (ExportLoc.isValid())
Diag(ExportLoc, diag::warn_template_export_unsupported);
return TemplateParameterList::Create(
Context, TemplateLoc, LAngleLoc,
llvm::makeArrayRef(, Params.size()),
RAngleLoc, RequiresClause);
static void SetNestedNameSpecifier(Sema &S, TagDecl *T,
const CXXScopeSpec &SS) {
if (SS.isSet())
DeclResult Sema::CheckClassTemplate(
Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
CXXScopeSpec &SS, IdentifierInfo *Name, SourceLocation NameLoc,
const ParsedAttributesView &Attr, TemplateParameterList *TemplateParams,
AccessSpecifier AS, SourceLocation ModulePrivateLoc,
SourceLocation FriendLoc, unsigned NumOuterTemplateParamLists,
TemplateParameterList **OuterTemplateParamLists, SkipBodyInfo *SkipBody) {
assert(TemplateParams && TemplateParams->size() > 0 &&
"No template parameters");
assert(TUK != TUK_Reference && "Can only declare or define class templates");
bool Invalid = false;
// Check that we can declare a template here.
if (CheckTemplateDeclScope(S, TemplateParams))
return true;
TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
assert(Kind != TTK_Enum && "can't build template of enumerated type");
// There is no such thing as an unnamed class template.
if (!Name) {
Diag(KWLoc, diag::err_template_unnamed_class);
return true;
// Find any previous declaration with this name. For a friend with no
// scope explicitly specified, we only look for tag declarations (per
// C++11 [basic.lookup.elab]p2).
DeclContext *SemanticContext;
LookupResult Previous(*this, Name, NameLoc,
(SS.isEmpty() && TUK == TUK_Friend)
? LookupTagName : LookupOrdinaryName,
if (SS.isNotEmpty() && !SS.isInvalid()) {
SemanticContext = computeDeclContext(SS, true);
if (!SemanticContext) {
// FIXME: Horrible, horrible hack! We can't currently represent this
// in the AST, and historically we have just ignored such friend
// class templates, so don't complain here.
Diag(NameLoc, TUK == TUK_Friend
? diag::warn_template_qualified_friend_ignored
: diag::err_template_qualified_declarator_no_match)
<< SS.getScopeRep() << SS.getRange();
return TUK != TUK_Friend;
if (RequireCompleteDeclContext(SS, SemanticContext))
return true;
// If we're adding a template to a dependent context, we may need to
// rebuilding some of the types used within the template parameter list,
// now that we know what the current instantiation is.
if (SemanticContext->isDependentContext()) {
ContextRAII SavedContext(*this, SemanticContext);
if (RebuildTemplateParamsInCurrentInstantiation(TemplateParams))
Invalid = true;
} else if (TUK != TUK_Friend && TUK != TUK_Reference)
diagnoseQualifiedDeclaration(SS, SemanticContext, Name, NameLoc, false);
LookupQualifiedName(Previous, SemanticContext);
} else {
SemanticContext = CurContext;
// C++14 [class.mem]p14:
// If T is the name of a class, then each of the following shall have a
// name different from T:
// -- every member template of class T
if (TUK != TUK_Friend &&
DeclarationNameInfo(Name, NameLoc)))
return true;
LookupName(Previous, S);
if (Previous.isAmbiguous())
return true;
NamedDecl *PrevDecl = nullptr;
if (Previous.begin() != Previous.end())
PrevDecl = (*Previous.begin())->getUnderlyingDecl();
if (PrevDecl && PrevDecl->isTemplateParameter()) {
// Maybe we will complain about the shadowed template parameter.
DiagnoseTemplateParameterShadow(NameLoc, PrevDecl);
// Just pretend that we didn't see the previous declaration.
PrevDecl = nullptr;
// If there is a previous declaration with the same name, check
// whether this is a valid redeclaration.
ClassTemplateDecl *PrevClassTemplate =
// We may have found the injected-class-name of a class template,
// class template partial specialization, or class template specialization.
// In these cases, grab the template that is being defined or specialized.
if (!PrevClassTemplate && PrevDecl && isa<CXXRecordDecl>(PrevDecl) &&
cast<CXXRecordDecl>(PrevDecl)->isInjectedClassName()) {
PrevDecl = cast<CXXRecordDecl>(PrevDecl->getDeclContext());
= cast<CXXRecordDecl>(PrevDecl)->getDescribedClassTemplate();
if (!PrevClassTemplate && isa<ClassTemplateSpecializationDecl>(PrevDecl)) {
= cast<ClassTemplateSpecializationDecl>(PrevDecl)
if (TUK == TUK_Friend) {
// C++ [namespace.memdef]p3:
// [...] When looking for a prior declaration of a class or a function
// declared as a friend, and when the name of the friend class or
// function is neither a qualified name nor a template-id, scopes outside
// the innermost enclosing namespace scope are not considered.
if (!SS.isSet()) {
DeclContext *OutermostContext = CurContext;
while (!OutermostContext->isFileContext())
OutermostContext = OutermostContext->getLookupParent();
if (PrevDecl &&
(OutermostContext->Equals(PrevDecl->getDeclContext()) ||
OutermostContext->Encloses(PrevDecl->getDeclContext()))) {
SemanticContext = PrevDecl->getDeclContext();
} else {
// Declarations in outer scopes don't matter. However, the outermost
// context we computed is the semantic context for our new
// declaration.
PrevDecl = PrevClassTemplate = nullptr;
SemanticContext = OutermostContext;
// Check that the chosen semantic context doesn't already contain a
// declaration of this name as a non-tag type.
DeclContext *LookupContext = SemanticContext;
while (LookupContext->isTransparentContext())
LookupContext = LookupContext->getLookupParent();
LookupQualifiedName(Previous, LookupContext);
if (Previous.isAmbiguous())
return true;
if (Previous.begin() != Previous.end())
PrevDecl = (*Previous.begin())->getUnderlyingDecl();
} else if (PrevDecl &&
!isDeclInScope(Previous.getRepresentativeDecl(), SemanticContext,
S, SS.isValid()))
PrevDecl = PrevClassTemplate = nullptr;
if (auto *Shadow = dyn_cast_or_null<UsingShadowDecl>(
PrevDecl ? Previous.getRepresentativeDecl() : nullptr)) {
if (SS.isEmpty() &&
!(PrevClassTemplate &&
SemanticContext->getRedeclContext()))) {
Diag(KWLoc, diag::err_using_decl_conflict_reverse);
Diag(Shadow->getUsingDecl()->getLocation(), diag::note_using_decl) << 0;
// Recover by ignoring the old declaration.
PrevDecl = PrevClassTemplate = nullptr;
// TODO Memory management; associated constraints are not always stored.
Expr *const CurAC = formAssociatedConstraints(TemplateParams, nullptr);
if (PrevClassTemplate) {
// Ensure that the template parameter lists are compatible. Skip this check
// for a friend in a dependent context: the template parameter list itself
// could be dependent.
if (!(TUK == TUK_Friend && CurContext->isDependentContext()) &&
return true;
// Check for matching associated constraints on redeclarations.
const Expr *const PrevAC = PrevClassTemplate->getAssociatedConstraints();
const bool RedeclACMismatch = [&] {
if (!(CurAC || PrevAC))
return false; // Nothing to check; no mismatch.
if (CurAC && PrevAC) {
llvm::FoldingSetNodeID CurACInfo, PrevACInfo;
CurAC->Profile(CurACInfo, Context, /*Canonical=*/true);
PrevAC->Profile(PrevACInfo, Context, /*Canonical=*/true);
if (CurACInfo == PrevACInfo)
return false; // All good; no mismatch.
return true;
if (RedeclACMismatch) {
Diag(CurAC ? CurAC->getBeginLoc() : NameLoc,
Diag(PrevAC ? PrevAC->getBeginLoc() : PrevClassTemplate->getLocation(),
<< /*declaration*/ 0;
return true;
// C++ [temp.class]p4:
// In a redeclaration, partial specialization, explicit
// specialization or explicit instantiation of a class template,
// the class-key shall agree in kind with the original class
// template declaration (
RecordDecl *PrevRecordDecl = PrevClassTemplate->getTemplatedDecl();
if (!isAcceptableTagRedeclaration(PrevRecordDecl, Kind,
TUK == TUK_Definition, KWLoc, Name)) {
Diag(KWLoc, diag::err_use_with_wrong_tag)
<< Name
<< FixItHint::CreateReplacement(KWLoc, PrevRecordDecl->getKindName());
Diag(PrevRecordDecl->getLocation(), diag::note_previous_use);
Kind = PrevRecordDecl->getTagKind();
// Check for redefinition of this class template.
if (TUK == TUK_Definition) {
if (TagDecl *Def = PrevRecordDecl->getDefinition()) {
// If we have a prior definition that is not visible, treat this as
// simply making that previous definition visible.
NamedDecl *Hidden = nullptr;
if (SkipBody && !hasVisibleDefinition(Def, &Hidden)) {
SkipBody->ShouldSkip = true;
SkipBody->Previous = Def;
auto *Tmpl = cast<CXXRecordDecl>(Hidden)->getDescribedClassTemplate();
assert(Tmpl && "original definition of a class template is not a "
"class template?");
} else {
Diag(NameLoc, diag::err_redefinition) << Name;
Diag(Def->getLocation(), diag::note_previous_definition);
// FIXME: Would it make sense to try to "forget" the previous
// definition, as part of error recovery?
return true;
} else if (PrevDecl) {
// C++ [temp]p5:
// A class template shall not have the same name as any other
// template, class, function, object, enumeration, enumerator,
// namespace, or type in the same scope (3.3), except as specified
// in (14.5.4).
Diag(NameLoc, diag::err_redefinition_different_kind) << Name;
Diag(PrevDecl->getLocation(), diag::note_previous_definition);
return true;
// Check the template parameter list of this declaration, possibly
// merging in the template parameter list from the previous class
// template declaration. Skip this check for a friend in a dependent
// context, because the template parameter list might be dependent.
if (!(TUK == TUK_Friend && CurContext->isDependentContext()) &&
? PrevClassTemplate->getMostRecentDecl()->getTemplateParameters()
: nullptr,
(SS.isSet() && SemanticContext && SemanticContext->isRecord() &&
? TPC_ClassTemplateMember
: TUK == TUK_Friend ? TPC_FriendClassTemplate : TPC_ClassTemplate,
Invalid = true;
if (SS.isSet()) {
// If the name of the template was qualified, we must be defining the
// template out-of-line.
if (!SS.isInvalid() && !Invalid && !PrevClassTemplate) {
Diag(NameLoc, TUK == TUK_Friend ? diag::err_friend_decl_does_not_match
: diag::err_member_decl_does_not_match)
<< Name << SemanticContext << /*IsDefinition*/true << SS.getRange();
Invalid = true;
// If this is a templated friend in a dependent context we should not put it
// on the redecl chain. In some cases, the templated friend can be the most
// recent declaration tricking the template instantiator to make substitutions
// there.
// FIXME: Figure out how to combine with shouldLinkDependentDeclWithPrevious
bool ShouldAddRedecl
= !(TUK == TUK_Friend && CurContext->isDependentContext());
CXXRecordDecl *NewClass =
CXXRecordDecl::Create(Context, Kind, SemanticContext, KWLoc, NameLoc, Name,
PrevClassTemplate && ShouldAddRedecl ?
PrevClassTemplate->getTemplatedDecl() : nullptr,
SetNestedNameSpecifier(*this, NewClass, SS);
if (NumOuterTemplateParamLists > 0)
Context, llvm::makeArrayRef(OuterTemplateParamLists,
// Add alignment attributes if necessary; these attributes are checked when
// the ASTContext lays out the structure.
if (TUK == TUK_Definition && (!SkipBody || !SkipBody->ShouldSkip)) {
// Attach the associated constraints when the declaration will not be part of
// a decl chain.
Expr *const ACtoAttach =
PrevClassTemplate && ShouldAddRedecl ? nullptr : CurAC;
ClassTemplateDecl *NewTemplate
= ClassTemplateDecl::Create(Context, SemanticContext, NameLoc,
DeclarationName(Name), TemplateParams,
NewClass, ACtoAttach);
if (ShouldAddRedecl)
if (ModulePrivateLoc.isValid())
// Build the type for the class template declaration now.
QualType T = NewTemplate->getInjectedClassNameSpecialization();
T = Context.getInjectedClassNameType(NewClass, T);
assert(T->isDependentType() && "Class template type is not dependent?");
// If we are providing an explicit specialization of a member that is a
// class template, make a note of that.
if (PrevClassTemplate &&
// Set the access specifier.
if (!Invalid && TUK != TUK_Friend && NewTemplate->getDeclContext()->isRecord())
SetMemberAccessSpecifier(NewTemplate, PrevClassTemplate, AS);
// Set the lexical context of these templates
if (TUK == TUK_Definition && (!SkipBody || !SkipBody->ShouldSkip))
ProcessDeclAttributeList(S, NewClass, Attr);
if (PrevClassTemplate)
mergeDeclAttributes(NewClass, PrevClassTemplate->getTemplatedDecl());
if (TUK != TUK_Friend) {
// Per C++ [basic.scope.temp]p2, skip the template parameter scopes.
Scope *Outer = S;
while ((Outer->getFlags() & Scope::TemplateParamScope) != 0)
Outer = Outer->getParent();
PushOnScopeChains(NewTemplate, Outer);
} else {
if (PrevClassTemplate && PrevClassTemplate->getAccess() != AS_none) {
// Friend templates are visible in fairly strange ways.
if (!CurContext->isDependentContext()) {
DeclContext *DC = SemanticContext->getRedeclContext();
if (Scope *EnclosingScope = getScopeForDeclContext(S, DC))
PushOnScopeChains(NewTemplate, EnclosingScope,
/* AddToContext = */ false);
FriendDecl *Friend = FriendDecl::Create(
Context, CurContext, NewClass->getLocation(), NewTemplate, FriendLoc);
if (PrevClassTemplate)
CheckRedeclarationModuleOwnership(NewTemplate, PrevClassTemplate);
if (Invalid) {
if (SkipBody && SkipBody->ShouldSkip)
return SkipBody->Previous;
return NewTemplate;
namespace {
/// Tree transform to "extract" a transformed type from a class template's
/// constructor to a deduction guide.
class ExtractTypeForDeductionGuide
: public TreeTransform<ExtractTypeForDeductionGuide> {
typedef TreeTransform<ExtractTypeForDeductionGuide> Base;
ExtractTypeForDeductionGuide(Sema &SemaRef) : Base(SemaRef) {}
TypeSourceInfo *transform(TypeSourceInfo *TSI) { return TransformType(TSI); }
QualType TransformTypedefType(TypeLocBuilder &TLB, TypedefTypeLoc TL) {
return TransformType(
/// 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) {}
Sema &SemaRef;
ClassTemplateDecl *Template;
DeclContext *DC = Template->getDeclContext();
CXXRecordDecl *Primary = Template->getTemplatedDecl();
DeclarationName DeductionGuideName =
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();
/// 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 = Template->getTemplateParameters();
if (FTD) {
TemplateParameterList *InnerParams = FTD->getTemplateParameters();
SmallVector<NamedDecl *, 16> AllParams;
AllParams.reserve(TemplateParams->size() + InnerParams->size());
TemplateParams->begin(), TemplateParams->end());
// 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;
NamedDecl *NewParam = transformTemplateParameter(Param, Args);
if (!NewParam)
return nullptr;
TemplateParams = TemplateParameterList::Create(
SemaRef.Context, InnerParams->getTemplateLoc(),
InnerParams->getLAngleLoc(), AllParams, InnerParams->getRAngleLoc(),
/*FIXME: RequiresClause*/ nullptr);
// 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;
if (FTD) {
FunctionProtoTypeLoc FPTL = CD->getTypeSourceInfo()->getTypeLoc()
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;
QualType NewType = transformFunctionProtoType(TLB, FPTL, Params, Args);
if (NewType.isNull())
return nullptr;
TypeSourceInfo *NewTInfo = TLB.getTypeSourceInfo(SemaRef.Context, NewType);
return buildDeductionGuide(TemplateParams, CD->getExplicitSpecifier(),
NewTInfo, CD->getBeginLoc(), CD->getLocation(),
/// 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);
FunctionProtoTypeLoc FPTL =
// Build the parameters, needed during deduction / substitution.
SmallVector<ParmVarDecl*, 4> Params;
for (auto T : ParamTypes) {
ParmVarDecl *NewParam = ParmVarDecl::Create(
SemaRef.Context, DC, Loc, Loc, nullptr, T,
SemaRef.Context.getTrivialTypeSourceInfo(T, Loc), SC_None, nullptr);
NewParam->setScopeInfo(0, Params.size());
FPTL.setParam(Params.size(), NewParam);
return buildDeductionGuide(Template->getTemplateParameters(),
ExplicitSpecifier(), TSI, Loc, Loc, Loc);
/// Transform a constructor template parameter into a deduction guide template
/// parameter, rebuilding any internal references to earlier parameters and
/// renumbering as we go.
NamedDecl *transformTemplateParameter(NamedDecl *TemplateParam,
MultiLevelTemplateArgumentList &Args) {
if (auto *TTP = dyn_cast<TemplateTypeParmDecl>(TemplateParam)) {
// TemplateTypeParmDecl's index cannot be changed after creation, so
// substitute it directly.
auto *NewTTP = TemplateTypeParmDecl::Create(
SemaRef.Context, DC, TTP->getBeginLoc(), TTP->getLocation(),
/*Depth*/ 0, Depth1IndexAdjustment + TTP->getIndex(),
TTP->getIdentifier(), TTP->wasDeclaredWithTypename(),
if (TTP->hasDefaultArgument()) {
TypeSourceInfo *InstantiatedDefaultArg =
SemaRef.SubstType(TTP->getDefaultArgumentInfo(), Args,
TTP->getDefaultArgumentLoc(), TTP->getDeclName());
if (InstantiatedDefaultArg)
return NewTTP;
if (auto *TTP = dyn_cast<TemplateTemplateParmDecl>(TemplateParam))
return transformTemplateParameterImpl(TTP, Args);
return transformTemplateParameterImpl(
cast<NonTypeTemplateParmDecl>(TemplateParam), Args);
template<typename TemplateParmDecl>
TemplateParmDecl *
transformTemplateParameterImpl(TemplateParmDecl *OldParam,
MultiLevelTemplateArgumentList &Args) {
// 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_or_null<TemplateParmDecl>(SemaRef.SubstDecl(OldParam, DC, Args));
assert(NewParam->getDepth() == 0 && "unexpected template param depth");
NewParam->setPosition(NewParam->getPosition() + Depth1IndexAdjustment);
return NewParam;
QualType transformFunctionProtoType(TypeLocBuilder &TLB,
FunctionProtoTypeLoc TL,
SmallVectorImpl<ParmVarDecl*> &Params,
MultiLevelTemplateArgumentList &Args) {
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 = transformFunctionTypeParam(OldParam, Args);
if (!NewParam)
return QualType();
// -- 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;
// 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);
for (unsigned I = 0, E = NewTL.getNumParams(); I != E; ++I)
NewTL.setParam(I, Params[I]);
return Result;
ParmVarDecl *
transformFunctionTypeParam(ParmVarDecl *OldParam,
MultiLevelTemplateArgumentList &Args) {
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::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, 0);
NewDI =
SemaRef.SubstType(PackTL.getPatternLoc(), Args,
OldParam->getLocation(), OldParam->getDeclName());
if (!NewDI) return nullptr;
NewDI =
SemaRef.CheckPackExpansion(NewDI, PackTL.getEllipsisLoc(),
} else
NewDI = SemaRef.SubstType(OldDI, Args, OldParam->getLocation(),
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).transform(NewDI);
// Resolving a wording defect, we also inherit default arguments from the
// constructor.
ExprResult NewDefArg;
if (OldParam->hasDefaultArg()) {
NewDefArg = SemaRef.SubstExpr(OldParam->getDefaultArg(), Args);
if (NewDefArg.isInvalid())
return nullptr;
ParmVarDecl *NewParam = ParmVarDecl::Create(SemaRef.Context, DC,
SemaRef.CurrentInstantiationScope->InstantiatedLocal(OldParam, NewParam);
return NewParam;
NamedDecl *buildDeductionGuide(TemplateParameterList *TemplateParams,
ExplicitSpecifier ES, TypeSourceInfo *TInfo,
SourceLocation LocStart, SourceLocation Loc,
SourceLocation LocEnd) {
DeclarationNameInfo Name(DeductionGuideName, Loc);
ArrayRef<ParmVarDecl *> Params =
// Build the implicit deduction guide template.
auto *Guide =
CXXDeductionGuideDecl::Create(SemaRef.Context, DC, LocStart, ES, Name,
TInfo->getType(), TInfo, LocEnd);
for (auto *Param : Params)
auto *GuideTemplate = FunctionTemplateDecl::Create(
SemaRef.Context, DC, Loc, DeductionGuideName, TemplateParams, Guide);
if (isa<CXXRecordDecl>(DC)) {
return GuideTemplate;
void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
SourceLocation Loc) {
if (CXXRecordDecl *DefRecord =
cast<CXXRecordDecl>(Template->getTemplatedDecl())->getDefinition()) {
TemplateDecl *DescribedTemplate = DefRecord->getDescribedClassTemplate();
Template = DescribedTemplate ? DescribedTemplate : Template;
DeclContext *DC = Template->getDeclContext();
if (DC->isDependentContext())
ConvertConstructorToDeductionGuideTransform Transform(
*this, cast<ClassTemplateDecl>(Template));
if (!isCompleteType(Loc, Transform.DeducedType))
// Check whether we've already declared deduction guides for this template.
// FIXME: Consider storing a flag on the template to indicate this.
auto Existing = DC->lookup(Transform.DeductionGuideName);
for (auto *D : Existing)
if (D->isImplicit())
// 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.
ArgumentPackSubstitutionIndexRAII SubstIndex(*this, -1);
// Create a template instantiation record to track the "instantiation" of
// constructors into deduction guides.
// FIXME: Add a kind for this to give more meaningful diagnostics. But can
// this substitution process actually fail?
InstantiatingTemplate BuildingDeductionGuides(*this, Loc, Template);
if (BuildingDeductionGuides.isInvalid())
// 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).
bool AddedAny = false;
for (NamedDecl *D : LookupConstructors(Transform.Primary)) {
D = D->getUnderlyingDecl();
if (D->isInvalidDecl() || D->isImplicit())
D = cast<NamedDecl>(D->getCanonicalDecl());
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()))
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)
// -- An additional function template derived as above from a hypothetical
// constructor C(C), called the copy deduction candidate.
/// Diagnose the presence of a default template argument on a
/// template parameter, which is ill-formed in certain contexts.
/// \returns true if the default template argument should be dropped.
static bool DiagnoseDefaultTemplateArgument(Sema &S,
Sema::TemplateParamListContext TPC,
SourceLocation ParamLoc,
SourceRange DefArgRange) {
switch (TPC) {
case Sema::TPC_ClassTemplate:
case Sema::TPC_VarTemplate:
case Sema::TPC_TypeAliasTemplate:
return false;
case Sema::TPC_FunctionTemplate:
case Sema::TPC_FriendFunctionTemplateDefinition:
// C++ [temp.param]p9:
// A default template-argument shall not be specified in a
// function template declaration or a function template
// definition [...]
// If a friend function template declaration specifies a default
// template-argument, that declaration shall be a definition and shall be
// the only declaration of the function template in the translation unit.
// (C++98/03 doesn't have this wording; see DR226).
S.Diag(ParamLoc, S.getLangOpts().CPlusPlus11 ?
: diag::ext_template_parameter_default_in_function_template)
<< DefArgRange;
return false;
case Sema::TPC_ClassTemplateMember:
// C++0x [temp.param]p9:
// A default template-argument shall not be specified in the
// template-parameter-lists of the definition of a member of a
// class template that appears outside of the member's class.
S.Diag(ParamLoc, diag::err_template_parameter_default_template_member)
<< DefArgRange;
return true;
case Sema::TPC_FriendClassTemplate:
case Sema::TPC_FriendFunctionTemplate:
// C++ [temp.param]p9:
// A default template-argument shall not be specified in a
// friend template declaration.
S.Diag(ParamLoc, diag::err_template_parameter_default_friend_template)
<< DefArgRange;
return true;
// FIXME: C++0x [temp.param]p9 allows default template-arguments
// for friend function templates if there is only a single
// declaration (and it is a definition). Strange!
llvm_unreachable("Invalid TemplateParamListContext!");
/// Check for unexpanded parameter packs within the template parameters
/// of a template template parameter, recursively.
static bool DiagnoseUnexpandedParameterPacks(Sema &S,
TemplateTemplateParmDecl *TTP) {
// A template template parameter which is a parameter pack is also a pack
// expansion.
if (TTP->isParameterPack())
return false;
TemplateParameterList *Params = TTP->getTemplateParameters();
for (unsigned I = 0, N = Params->size(); I != N; ++I) {
NamedDecl *P = Params->getParam(I);
if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(P)) {
if (!NTTP->isParameterPack() &&
return true;
if (TemplateTemplateParmDecl *InnerTTP
= dyn_cast<TemplateTemplateParmDecl>(P))
if (DiagnoseUnexpandedParameterPacks(S, InnerTTP))
return true;
return false;
/// Checks the validity of a template parameter list, possibly
/// considering the template parameter list from a previous
/// declaration.
/// If an "old" template parameter list is provided, it must be
/// equivalent (per TemplateParameterListsAreEqual) to the "new"
/// template parameter list.
/// \param NewParams Template parameter list for a new template
/// declaration. This template parameter list will be updated with any
/// default arguments that are carried through from the previous
/// template parameter list.
/// \param OldParams If provided, template parameter list from a
/// previous declaration of the same template. Default template
/// arguments will be merged from the old template parameter list to
/// the new template parameter list.
/// \param TPC Describes the context in which we are checking the given
/// template parameter list.
/// \param SkipBody If we might have already made a prior merged definition
/// of this template visible, the corresponding body-skipping information.
/// Default argument redefinition is not an error when skipping such a body,
/// because (under the ODR) we can assume the default arguments are the same
/// as the prior merged definition.
/// \returns true if an error occurred, false otherwise.
bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
TemplateParameterList *OldParams,
TemplateParamListContext TPC,
SkipBodyInfo *SkipBody) {
bool Invalid = false;
// C++ [temp.param]p10:
// The set of default template-arguments available for use with a
// template declaration or definition is obtained by merging the
// default arguments from the definition (if in scope) and all
// declarations in scope in the same way default function
// arguments are (8.3.6).
bool SawDefaultArgument = false;
SourceLocation PreviousDefaultArgLoc;
// Dummy initialization to avoid warnings.
TemplateParameterList::iterator OldParam = NewParams->end();
if (OldParams)
OldParam = OldParams->begin();
bool RemoveDefaultArguments = false;
for (TemplateParameterList::iterator NewParam = NewParams->begin(),
NewParamEnd = NewParams->end();
NewParam != NewParamEnd; ++NewParam) {
// Variables used to diagnose redundant default arguments
bool RedundantDefaultArg = false;
SourceLocation OldDefaultLoc;
SourceLocation NewDefaultLoc;
// Variable used to diagnose missing default arguments
bool MissingDefaultArg = false;
// Variable used to diagnose non-final parameter packs
bool SawParameterPack = false;
if (TemplateTypeParmDecl *NewTypeParm
= dyn_cast<TemplateTypeParmDecl>(*NewParam)) {
// Check the presence of a default argument here.
if (NewTypeParm->hasDefaultArgument() &&
DiagnoseDefaultTemplateArgument(*this, TPC,
// Merge default arguments for template type parameters.
TemplateTypeParmDecl *OldTypeParm
= OldParams? cast<TemplateTypeParmDecl>(*OldParam) : nullptr;
if (NewTypeParm->isParameterPack()) {
assert(!NewTypeParm->hasDefaultArgument() &&
"Parameter packs can't have a default argument!");
SawParameterPack = true;
} else if (OldTypeParm && hasVisibleDefaultArgument(OldTypeParm) &&
NewTypeParm->hasDefaultArgument() &&
(!SkipBody || !SkipBody->ShouldSkip)) {
OldDefaultLoc = OldTypeParm->getDefaultArgumentLoc();
NewDefaultLoc = NewTypeParm->getDefaultArgumentLoc();
SawDefaultArgument = true;
RedundantDefaultArg = true;
PreviousDefaultArgLoc = NewDefaultLoc;
} else if (OldTypeParm && OldTypeParm->hasDefaultArgument()) {
// Merge the default argument from the old declaration to the
// new declaration.
NewTypeParm->setInheritedDefaultArgument(Context, OldTypeParm);
PreviousDefaultArgLoc = OldTypeParm->getDefaultArgumentLoc();
} else if (NewTypeParm->hasDefaultArgument()) {
SawDefaultArgument = true;
PreviousDefaultArgLoc = NewTypeParm->getDefaultArgumentLoc();
} else if (SawDefaultArgument)
MissingDefaultArg = true;
} else if (NonTypeTemplateParmDecl *NewNonTypeParm
= dyn_cast<NonTypeTemplateParmDecl>(*NewParam)) {
// Check for unexpanded parameter packs.
if (!NewNonTypeParm->isParameterPack() &&
UPPC_NonTypeTemplateParameterType)) {
Invalid = true;
// Check the presence of a default argument here.
if (NewNonTypeParm->hasDefaultArgument() &&
DiagnoseDefaultTemplateArgument(*this, TPC,
NewNonTypeParm->getDefaultArgument()->getSourceRange())) {
// Merge default arguments for non-type template parameters
NonTypeTemplateParmDecl *OldNonTypeParm
= OldParams? cast<NonTypeTemplateParmDecl>(*OldParam) : nullptr;
if (NewNonTypeParm->isParameterPack()) {
assert(!NewNonTypeParm->hasDefaultArgument() &&
"Parameter packs can't have a default argument!");
if (!NewNonTypeParm->isPackExpansion())
SawParameterPack = true;
} else if (OldNonTypeParm && hasVisibleDefaultArgument(OldNonTypeParm) &&
NewNonTypeParm->hasDefaultArgument() &&
(!SkipBody || !SkipBody->ShouldSkip)) {
OldDefaultLoc = OldNonTypeParm->getDefaultArgumentLoc();
NewDefaultLoc = NewNonTypeParm->getDefaultArgumentLoc();
SawDefaultArgument = true;
RedundantDefaultArg = true;
PreviousDefaultArgLoc = NewDefaultLoc;
} else if (OldNonTypeParm && OldNonTypeParm->hasDefaultArgument()) {
// Merge the default argument from the old declaration to the
// new declaration.
NewNonTypeParm->setInheritedDefaultArgument(Context, OldNonTypeParm);
PreviousDefaultArgLoc = OldNonTypeParm->getDefaultArgumentLoc();
} else if (NewNonTypeParm->hasDefaultArgument()) {
SawDefaultArgument = true;
PreviousDefaultArgLoc = NewNonTypeParm->getDefaultArgumentLoc();
} else if (SawDefaultArgument)
MissingDefaultArg = true;
} else {
TemplateTemplateParmDecl *NewTemplateParm
= cast<TemplateTemplateParmDecl>(*NewParam);
// Check for unexpanded parameter packs, recursively.
if (::DiagnoseUnexpandedParameterPacks(*this, NewTemplateParm)) {
Invalid = true;
// Check the presence of a default argument here.
if (NewTemplateParm->hasDefaultArgument() &&
DiagnoseDefaultTemplateArgument(*this, TPC,
// Merge default arguments for template template parameters
TemplateTemplateParmDecl *OldTemplateParm
= OldParams? cast<TemplateTemplateParmDecl>(*OldParam) : nullptr;
if (NewTemplateParm->isParameterPack()) {
assert(!NewTemplateParm->hasDefaultArgument() &&
"Parameter packs can't have a default argument!");
if (!NewTemplateParm->isPackExpansion())
SawParameterPack = true;
} else if (OldTemplateParm &&
hasVisibleDefaultArgument(OldTemplateParm) &&
NewTemplateParm->hasDefaultArgument() &&
(!SkipBody || !SkipBody->ShouldSkip)) {
OldDefaultLoc = OldTemplateParm->getDefaultArgument().getLocation();
NewDefaultLoc = NewTemplateParm->getDefaultArgument().getLocation();
SawDefaultArgument = true;
RedundantDefaultArg = true;
PreviousDefaultArgLoc = NewDefaultLoc;
} else if (OldTemplateParm && OldTemplateParm->hasDefaultArgument()) {
// Merge the default argument from the old declaration to the
// new declaration.
NewTemplateParm->setInheritedDefaultArgument(Context, OldTemplateParm);
= OldTemplateParm->getDefaultArgument().getLocation();
} else if (NewTemplateParm->hasDefaultArgument()) {
SawDefaultArgument = true;
= NewTemplateParm->getDefaultArgument().getLocation();
} else if (SawDefaultArgument)
MissingDefaultArg = true;
// C++11 [temp.param]p11:
// If a template parameter of a primary class template or alias template
// is a template parameter pack, it shall be the last template parameter.
if (SawParameterPack && (NewParam + 1) != NewParamEnd &&
(TPC == TPC_ClassTemplate || TPC == TPC_VarTemplate ||
TPC == TPC_TypeAliasTemplate)) {
Invalid = true;
if (RedundantDefaultArg) {
// C++ [temp.param]p12:
// A template-parameter shall not be given default arguments
// by two different declarations in the same scope.
Diag(NewDefaultLoc, diag::err_template_param_default_arg_redefinition);
Diag(OldDefaultLoc, diag::note_template_param_prev_default_arg);
Invalid = true;
} else if (MissingDefaultArg && TPC != TPC_FunctionTemplate) {
// C++ [temp.param]p11:
// If a template-parameter of a class template has a default
// template-argument, each subsequent template-parameter shall either
// have a default template-argument supplied or be a template parameter
// pack.
Diag(PreviousDefaultArgLoc, diag::note_template_param_prev_default_arg);
Invalid = true;
RemoveDefaultArguments = true;
// If we have an old template parameter list that we're merging
// in, move on to the next parameter.
if (OldParams)
// We were missing some default arguments at the end of the list, so remove
// all of the default arguments.
if (RemoveDefaultArguments) {
for (TemplateParameterList::iterator NewParam = NewParams->begin(),
NewParamEnd = NewParams->end();
NewParam != NewParamEnd; ++NewParam) {
if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*NewParam))
else if (NonTypeTemplateParmDecl *NTTP
= dyn_cast<NonTypeTemplateParmDecl>(*NewParam))
return Invalid;
namespace {
/// A class which looks for a use of a certain level of template
/// parameter.
struct DependencyChecker : RecursiveASTVisitor<DependencyChecker> {
typedef RecursiveASTVisitor<DependencyChecker> super;
unsigned Depth;
// Whether we're looking for a use of a template parameter that makes the
// overall construct type-dependent / a dependent type. This is strictly
// best-effort for now; we may fail to match at all for a dependent type
// in some cases if this is set.
bool IgnoreNonTypeDependent;
bool Match;
SourceLocation MatchLoc;
DependencyChecker(unsigned Depth, bool IgnoreNonTypeDependent)
: Depth(Depth), IgnoreNonTypeDependent(IgnoreNonTypeDependent),
Match(false) {}
DependencyChecker(TemplateParameterList *Params, bool IgnoreNonTypeDependent)
: IgnoreNonTypeDependent(IgnoreNonTypeDependent), Match(false) {
NamedDecl *ND = Params->getParam(0);
if (TemplateTypeParmDecl *PD = dyn_cast<TemplateTypeParmDecl>(ND)) {
Depth = PD->getDepth();
} else if (NonTypeTemplateParmDecl *PD =
dyn_cast<NonTypeTemplateParmDecl>(ND)) {
Depth = PD->getDepth();
} else {
Depth = cast<TemplateTemplateParmDecl>(ND)->getDepth();
bool Matches(unsigned ParmDepth, SourceLocation Loc = SourceLocation()) {
if (ParmDepth >= Depth) {
Match = true;
MatchLoc = Loc;
return true;
return false;
bool TraverseStmt(Stmt *S, DataRecursionQueue *Q = nullptr) {
// Prune out non-type-dependent expressions if requested. This can
// sometimes result in us failing to find a template parameter reference
// (if a value-dependent expression creates a dependent type), but this
// mode is best-effort only.
if (auto *E = dyn_cast_or_null<Expr>(S))
if (IgnoreNonTypeDependent && !E->isTypeDependent())
return true;
return super::TraverseStmt(S, Q);
bool TraverseTypeLoc(TypeLoc TL) {
if (IgnoreNonTypeDependent && !TL.isNull() &&
return true;
return super::TraverseTypeLoc(TL);
bool VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TL) {
return !Matches(TL.getTypePtr()->getDepth(), TL.getNameLoc());
bool VisitTemplateTypeParmType(const TemplateTypeParmType *T) {
// For a best-effort search, keep looking until we find a location.
return IgnoreNonTypeDependent || !Matches(T->getDepth());
bool TraverseTemplateName(TemplateName N) {
if (TemplateTemplateParmDecl *PD =
if (Matches(PD->getDepth()))
return false;
return super::TraverseTemplateName(N);
bool VisitDeclRefExpr(DeclRefExpr *E) {
if (NonTypeTemplateParmDecl *PD =
if (Matches(PD->getDepth(), E->getExprLoc()))
return false;
return super::VisitDeclRefExpr(E);
bool VisitSubstTemplateTypeParmType(const SubstTemplateTypeParmType *T) {
return TraverseType(T->getReplacementType());
VisitSubstTemplateTypeParmPackType(const SubstTemplateTypeParmPackType *T) {
return TraverseTemplateArgument(T->getArgumentPack());
bool TraverseInjectedClassNameType(const InjectedClassNameType *T) {
return TraverseType(T->getInjectedSpecializationType());
} // end anonymous namespace
/// Determines whether a given type depends on the given parameter
/// list.
static bool
DependsOnTemplateParameters(QualType T, TemplateParameterList *Params) {
DependencyChecker Checker(Params, /*IgnoreNonTypeDependent*/false);
return Checker.Match;
// Find the source range corresponding to the named type in the given
// nested-name-specifier, if any.
static SourceRange getRangeOfTypeInNestedNameSpecifier(ASTContext &Context,
QualType T,
const CXXScopeSpec &SS) {
NestedNameSpecifierLoc NNSLoc(SS.getScopeRep(), SS.location_data());
while (NestedNameSpecifier *NNS = NNSLoc.getNestedNameSpecifier()) {
if (const Type *CurType = NNS->getAsType()) {
if (Context.hasSameUnqualifiedType(T, QualType(CurType, 0)))
return NNSLoc.getTypeLoc().getSourceRange();
} else
NNSLoc = NNSLoc.getPrefix();
return SourceRange();
/// Match the given template parameter lists to the given scope
/// specifier, returning the template parameter list that applies to the
/// name.
/// \param DeclStartLoc the start of the declaration that has a scope
/// specifier or a template parameter list.
/// \param DeclLoc The location of the declaration itself.
/// \param SS the scope specifier that will be matched to the given template
/// parameter lists. This scope specifier precedes a qualified name that is
/// being declared.
/// \param TemplateId The template-id following the scope specifier, if there
/// is one. Used to check for a missing 'template<>'.
/// \param ParamLists the template parameter lists, from the outermost to the
/// innermost template parameter lists.
/// \param IsFriend Whether to apply the slightly different rules for
/// matching template parameters to scope specifiers in friend
/// declarations.
/// \param IsMemberSpecialization will be set true if the scope specifier
/// denotes a fully-specialized type, and therefore this is a declaration of
/// a member specialization.
/// \returns the template parameter list, if any, that corresponds to the
/// name that is preceded by the scope specifier @p SS. This template
/// parameter list may have template parameters (if we're declaring a
/// template) or may have no template parameters (if we're declaring a
/// template specialization), or may be NULL (if what we're declaring isn't
/// itself a template).
TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
SourceLocation DeclStartLoc, SourceLocation DeclLoc, const CXXScopeSpec &SS,
TemplateIdAnnotation *TemplateId,
ArrayRef<TemplateParameterList *> ParamLists, bool IsFriend,
bool &IsMemberSpecialization, bool &Invalid) {
IsMemberSpecialization = false;
Invalid = false;
// The sequence of nested types to which we will match up the template
// parameter lists. We first build this list by starting with the type named
// by the nested-name-specifier and walking out until we run out of types.
SmallVector<QualType, 4> NestedTypes;
QualType T;
if (SS.getScopeRep()) {
if (CXXRecordDecl *Record
= dyn_cast_or_null<CXXRecordDecl>(computeDeclContext(SS, true)))
T = Context.getTypeDeclType(Record);
T = QualType(SS.getScopeRep()->getAsType(), 0);
// If we found an explicit specialization that prevents us from needing
// 'template<>' headers, this will be set to the location of that
// explicit specialization.
SourceLocation ExplicitSpecLoc;
while (!T.isNull()) {
// Retrieve the parent of a record type.
if (CXXRecordDecl *Record = T->getAsCXXRecordDecl()) {
// If this type is an explicit specialization, we're done.
if (ClassTemplateSpecializationDecl *Spec
= dyn_cast<ClassTemplateSpecializationDecl>(Record)) {
if (!isa<ClassTemplatePartialSpecializationDecl>(Spec) &&
Spec->getSpecializationKind() == TSK_ExplicitSpecialization) {
ExplicitSpecLoc = Spec->getLocation();
} else if (Record->getTemplateSpecializationKind()
== TSK_ExplicitSpecialization) {
ExplicitSpecLoc = Record->getLocation();
if (TypeDecl *Parent = dyn_cast<TypeDecl>(Record->getParent()))
T = Context.getTypeDeclType(Parent);
T = QualType();
if (const TemplateSpecializationType *TST
= T->getAs<TemplateSpecializationType>()) {
if (TemplateDecl *Template = TST->getTemplateName().getAsTemplateDecl()) {
if (TypeDecl *Parent = dyn_cast<TypeDecl>(Template->getDeclContext()))
T = Context.getTypeDeclType(Parent);
T = QualType();
// Look one step prior in a dependent template specialization type.
if (const DependentTemplateSpecializationType *DependentTST
= T->getAs<DependentTemplateSpecializationType>()) {
if (NestedNameSpecifier *NNS = DependentTST->getQualifier())
T = QualType(NNS->getAsType(), 0);
T = QualType();
// Look one step prior in a dependent name type.
if (const DependentNameType *DependentName = T->getAs<DependentNameType>()){
if (NestedNameSpecifier *NNS = DependentName->getQualifier())
T = QualType(NNS->getAsType(), 0);
T = QualType();
// Retrieve the parent of an enumeration type.
if (const EnumType *EnumT = T->getAs<EnumType>()) {
// FIXME: Forward-declared enums require a TSK_ExplicitSpecialization
// check here.
EnumDecl *Enum = EnumT->getDecl();
// Get to the parent type.
if (TypeDecl *Parent = dyn_cast<TypeDecl>(Enum->getParent()))
T = Context.getTypeDeclType(Parent);
T = QualType();
T = QualType();
// Reverse the nested types list, since we want to traverse from the outermost
// to the innermost while checking template-parameter-lists.
std::reverse(NestedTypes.begin(), NestedTypes.end());
// C++0x [temp.expl.spec]p17:
// A member or a member template may be nested within many
// enclosing class templates. In an explicit specialization for
// such a member, the member declaration shall be preceded by a
// template<> for each enclosing class template that is
// explicitly specialized.
bool SawNonEmptyTemplateParameterList = false;
auto CheckExplicitSpecialization = [&](SourceRange Range, bool Recovery) {
if (SawNonEmptyTemplateParameterList) {
Diag(DeclLoc, diag::err_specialize_member_of_template)
<< !Recovery << Range;
Invalid = true;
IsMemberSpecialization = false;
return true;
return false;
auto DiagnoseMissingExplicitSpecialization = [&] (SourceRange Range) {
// Check that we can have an explicit specialization here.
if (CheckExplicitSpecialization(Range, true))
return true;
// We don't have a template header, but we should.
SourceLocation ExpectedTemplateLoc;
if (!ParamLists.empty())
ExpectedTemplateLoc = ParamLists[0]->getTemplateLoc();
ExpectedTemplateLoc = DeclStartLoc;
Diag(DeclLoc, diag::err_template_spec_needs_header)
<< Range
<< FixItHint::CreateInsertion(ExpectedTemplateLoc, "template<> ");
return false;
unsigned ParamIdx = 0;
for (unsigned TypeIdx = 0, NumTypes = NestedTypes.size(); TypeIdx != NumTypes;
++TypeIdx) {
T = NestedTypes[TypeIdx];
// Whether we expect a 'template<>' header.
bool NeedEmptyTemplateHeader = false;
// Whether we expect a template header with parameters.
bool NeedNonemptyTemplateHeader = false;
// For a dependent type, the set of template parameters that we
// expect to see.
TemplateParameterList *ExpectedTemplateParams = nullptr;
// C++0x [temp.expl.spec]p15:
// A member or a member template may be nested within many enclosing
// class templates. In an explicit specialization for such a member, the
// member declaration shall be preceded by a template<> for each