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//===--- SemaLambda.cpp - Semantic Analysis for C++11 Lambdas -------------===//
// 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++ lambda expressions.
#include "clang/Sema/DeclSpec.h"
#include "TypeLocBuilder.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/ExprCXX.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/SemaLambda.h"
#include "llvm/ADT/STLExtras.h"
using namespace clang;
using namespace sema;
/// Examines the FunctionScopeInfo stack to determine the nearest
/// enclosing lambda (to the current lambda) that is 'capture-ready' for
/// the variable referenced in the current lambda (i.e. \p VarToCapture).
/// If successful, returns the index into Sema's FunctionScopeInfo stack
/// of the capture-ready lambda's LambdaScopeInfo.
/// Climbs down the stack of lambdas (deepest nested lambda - i.e. current
/// lambda - is on top) to determine the index of the nearest enclosing/outer
/// lambda that is ready to capture the \p VarToCapture being referenced in
/// the current lambda.
/// As we climb down the stack, we want the index of the first such lambda -
/// that is the lambda with the highest index that is 'capture-ready'.
/// A lambda 'L' is capture-ready for 'V' (var or this) if:
/// - its enclosing context is non-dependent
/// - and if the chain of lambdas between L and the lambda in which
/// V is potentially used (i.e. the lambda at the top of the scope info
/// stack), can all capture or have already captured V.
/// If \p VarToCapture is 'null' then we are trying to capture 'this'.
/// Note that a lambda that is deemed 'capture-ready' still needs to be checked
/// for whether it is 'capture-capable' (see
/// getStackIndexOfNearestEnclosingCaptureCapableLambda), before it can truly
/// capture.
/// \param FunctionScopes - Sema's stack of nested FunctionScopeInfo's (which a
/// LambdaScopeInfo inherits from). The current/deepest/innermost lambda
/// is at the top of the stack and has the highest index.
/// \param VarToCapture - the variable to capture. If NULL, capture 'this'.
/// \returns An Optional<unsigned> Index that if evaluates to 'true' contains
/// the index (into Sema's FunctionScopeInfo stack) of the innermost lambda
/// which is capture-ready. If the return value evaluates to 'false' then
/// no lambda is capture-ready for \p VarToCapture.
static inline Optional<unsigned>
ArrayRef<const clang::sema::FunctionScopeInfo *> FunctionScopes,
VarDecl *VarToCapture) {
// Label failure to capture.
const Optional<unsigned> NoLambdaIsCaptureReady;
// Ignore all inner captured regions.
unsigned CurScopeIndex = FunctionScopes.size() - 1;
while (CurScopeIndex > 0 && isa<clang::sema::CapturedRegionScopeInfo>(
isa<clang::sema::LambdaScopeInfo>(FunctionScopes[CurScopeIndex]) &&
"The function on the top of sema's function-info stack must be a lambda");
// If VarToCapture is null, we are attempting to capture 'this'.
const bool IsCapturingThis = !VarToCapture;
const bool IsCapturingVariable = !IsCapturingThis;
// Start with the current lambda at the top of the stack (highest index).
DeclContext *EnclosingDC =
do {
const clang::sema::LambdaScopeInfo *LSI =
// IF we have climbed down to an intervening enclosing lambda that contains
// the variable declaration - it obviously can/must not capture the
// variable.
// Since its enclosing DC is dependent, all the lambdas between it and the
// innermost nested lambda are dependent (otherwise we wouldn't have
// arrived here) - so we don't yet have a lambda that can capture the
// variable.
if (IsCapturingVariable &&
return NoLambdaIsCaptureReady;
// For an enclosing lambda to be capture ready for an entity, all
// intervening lambda's have to be able to capture that entity. If even
// one of the intervening lambda's is not capable of capturing the entity
// then no enclosing lambda can ever capture that entity.
// For e.g.
// const int x = 10;
// [=](auto a) { #1
// [](auto b) { #2 <-- an intervening lambda that can never capture 'x'
// [=](auto c) { #3
// f(x, c); <-- can not lead to x's speculative capture by #1 or #2
// }; }; };
// If they do not have a default implicit capture, check to see
// if the entity has already been explicitly captured.
// If even a single dependent enclosing lambda lacks the capability
// to ever capture this variable, there is no further enclosing
// non-dependent lambda that can capture this variable.
if (LSI->ImpCaptureStyle == sema::LambdaScopeInfo::ImpCap_None) {
if (IsCapturingVariable && !LSI->isCaptured(VarToCapture))
return NoLambdaIsCaptureReady;
if (IsCapturingThis && !LSI->isCXXThisCaptured())
return NoLambdaIsCaptureReady;
EnclosingDC = getLambdaAwareParentOfDeclContext(EnclosingDC);
} while (!EnclosingDC->isTranslationUnit() &&
EnclosingDC->isDependentContext() &&
assert(CurScopeIndex < (FunctionScopes.size() - 1));
// If the enclosingDC is not dependent, then the immediately nested lambda
// (one index above) is capture-ready.
if (!EnclosingDC->isDependentContext())
return CurScopeIndex + 1;
return NoLambdaIsCaptureReady;
/// Examines the FunctionScopeInfo stack to determine the nearest
/// enclosing lambda (to the current lambda) that is 'capture-capable' for
/// the variable referenced in the current lambda (i.e. \p VarToCapture).
/// If successful, returns the index into Sema's FunctionScopeInfo stack
/// of the capture-capable lambda's LambdaScopeInfo.
/// Given the current stack of lambdas being processed by Sema and
/// the variable of interest, to identify the nearest enclosing lambda (to the
/// current lambda at the top of the stack) that can truly capture
/// a variable, it has to have the following two properties:
/// a) 'capture-ready' - be the innermost lambda that is 'capture-ready':
/// - climb down the stack (i.e. starting from the innermost and examining
/// each outer lambda step by step) checking if each enclosing
/// lambda can either implicitly or explicitly capture the variable.
/// Record the first such lambda that is enclosed in a non-dependent
/// context. If no such lambda currently exists return failure.
/// b) 'capture-capable' - make sure the 'capture-ready' lambda can truly
/// capture the variable by checking all its enclosing lambdas:
/// - check if all outer lambdas enclosing the 'capture-ready' lambda
/// identified above in 'a' can also capture the variable (this is done
/// via tryCaptureVariable for variables and CheckCXXThisCapture for
/// 'this' by passing in the index of the Lambda identified in step 'a')
/// \param FunctionScopes - Sema's stack of nested FunctionScopeInfo's (which a
/// LambdaScopeInfo inherits from). The current/deepest/innermost lambda
/// is at the top of the stack.
/// \param VarToCapture - the variable to capture. If NULL, capture 'this'.
/// \returns An Optional<unsigned> Index that if evaluates to 'true' contains
/// the index (into Sema's FunctionScopeInfo stack) of the innermost lambda
/// which is capture-capable. If the return value evaluates to 'false' then
/// no lambda is capture-capable for \p VarToCapture.
Optional<unsigned> clang::getStackIndexOfNearestEnclosingCaptureCapableLambda(
ArrayRef<const sema::FunctionScopeInfo *> FunctionScopes,
VarDecl *VarToCapture, Sema &S) {
const Optional<unsigned> NoLambdaIsCaptureCapable;
const Optional<unsigned> OptionalStackIndex =
if (!OptionalStackIndex)
return NoLambdaIsCaptureCapable;
const unsigned IndexOfCaptureReadyLambda = OptionalStackIndex.getValue();
assert(((IndexOfCaptureReadyLambda != (FunctionScopes.size() - 1)) ||
S.getCurGenericLambda()) &&
"The capture ready lambda for a potential capture can only be the "
"current lambda if it is a generic lambda");
const sema::LambdaScopeInfo *const CaptureReadyLambdaLSI =
// If VarToCapture is null, we are attempting to capture 'this'
const bool IsCapturingThis = !VarToCapture;
const bool IsCapturingVariable = !IsCapturingThis;
if (IsCapturingVariable) {
// Check if the capture-ready lambda can truly capture the variable, by
// checking whether all enclosing lambdas of the capture-ready lambda allow
// the capture - i.e. make sure it is capture-capable.
QualType CaptureType, DeclRefType;
const bool CanCaptureVariable =
/*ExprVarIsUsedInLoc*/ SourceLocation(),
/*EllipsisLoc*/ SourceLocation(),
/*BuildAndDiagnose*/ false, CaptureType,
DeclRefType, &IndexOfCaptureReadyLambda);
if (!CanCaptureVariable)
return NoLambdaIsCaptureCapable;
} else {
// Check if the capture-ready lambda can truly capture 'this' by checking
// whether all enclosing lambdas of the capture-ready lambda can capture
// 'this'.
const bool CanCaptureThis =
/*Explicit*/ false, /*BuildAndDiagnose*/ false,
if (!CanCaptureThis)
return NoLambdaIsCaptureCapable;
return IndexOfCaptureReadyLambda;
static inline TemplateParameterList *
getGenericLambdaTemplateParameterList(LambdaScopeInfo *LSI, Sema &SemaRef) {
if (!LSI->GLTemplateParameterList && !LSI->TemplateParams.empty()) {
LSI->GLTemplateParameterList = TemplateParameterList::Create(
/*Template kw loc*/ SourceLocation(),
/*L angle loc*/ LSI->ExplicitTemplateParamsRange.getBegin(),
/*R angle loc*/LSI->ExplicitTemplateParamsRange.getEnd(),
return LSI->GLTemplateParameterList;
CXXRecordDecl *Sema::createLambdaClosureType(SourceRange IntroducerRange,
TypeSourceInfo *Info,
bool KnownDependent,
LambdaCaptureDefault CaptureDefault) {
DeclContext *DC = CurContext;
while (!(DC->isFunctionOrMethod() || DC->isRecord() || DC->isFileContext()))
DC = DC->getParent();
bool IsGenericLambda = getGenericLambdaTemplateParameterList(getCurLambda(),
// Start constructing the lambda class.
CXXRecordDecl *Class = CXXRecordDecl::CreateLambda(Context, DC, Info,
return Class;
/// Determine whether the given context is or is enclosed in an inline
/// function.
static bool isInInlineFunction(const DeclContext *DC) {
while (!DC->isFileContext()) {
if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(DC))
if (FD->isInlined())
return true;
DC = DC->getLexicalParent();
return false;
std::tuple<MangleNumberingContext *, Decl *>
Sema::getCurrentMangleNumberContext(const DeclContext *DC) {
// Compute the context for allocating mangling numbers in the current
// expression, if the ABI requires them.
Decl *ManglingContextDecl = ExprEvalContexts.back().ManglingContextDecl;
enum ContextKind {
} Kind = Normal;
// Default arguments of member function parameters that appear in a class
// definition, as well as the initializers of data members, receive special
// treatment. Identify them.
if (ManglingContextDecl) {
if (ParmVarDecl *Param = dyn_cast<ParmVarDecl>(ManglingContextDecl)) {
if (const DeclContext *LexicalDC
= Param->getDeclContext()->getLexicalParent())
if (LexicalDC->isRecord())
Kind = DefaultArgument;
} else if (VarDecl *Var = dyn_cast<VarDecl>(ManglingContextDecl)) {
if (Var->getDeclContext()->isRecord())
Kind = StaticDataMember;
else if (Var->getMostRecentDecl()->isInline())
Kind = InlineVariable;
else if (Var->getDescribedVarTemplate())
Kind = VariableTemplate;
else if (auto *VTS = dyn_cast<VarTemplateSpecializationDecl>(Var)) {
if (!VTS->isExplicitSpecialization())
Kind = VariableTemplate;
} else if (isa<FieldDecl>(ManglingContextDecl)) {
Kind = DataMember;
// Itanium ABI [5.1.7]:
// In the following contexts [...] the one-definition rule requires closure
// types in different translation units to "correspond":
bool IsInNonspecializedTemplate =
inTemplateInstantiation() || CurContext->isDependentContext();
switch (Kind) {
case Normal: {
// -- the bodies of non-exported nonspecialized template functions
// -- the bodies of inline functions
if ((IsInNonspecializedTemplate &&
!(ManglingContextDecl && isa<ParmVarDecl>(ManglingContextDecl))) ||
isInInlineFunction(CurContext)) {
while (auto *CD = dyn_cast<CapturedDecl>(DC))
DC = CD->getParent();
return std::make_tuple(&Context.getManglingNumberContext(DC), nullptr);
return std::make_tuple(nullptr, nullptr);
case StaticDataMember:
// -- the initializers of nonspecialized static members of template classes
if (!IsInNonspecializedTemplate)
return std::make_tuple(nullptr, ManglingContextDecl);
// Fall through to get the current context.
case DataMember:
// -- the in-class initializers of class members
case DefaultArgument:
// -- default arguments appearing in class definitions
case InlineVariable:
// -- the initializers of inline variables
case VariableTemplate:
// -- the initializers of templated variables
return std::make_tuple(
llvm_unreachable("unexpected context");
CXXMethodDecl *Sema::startLambdaDefinition(CXXRecordDecl *Class,
SourceRange IntroducerRange,
TypeSourceInfo *MethodTypeInfo,
SourceLocation EndLoc,
ArrayRef<ParmVarDecl *> Params,
ConstexprSpecKind ConstexprKind) {
QualType MethodType = MethodTypeInfo->getType();
TemplateParameterList *TemplateParams =
getGenericLambdaTemplateParameterList(getCurLambda(), *this);
// If a lambda appears in a dependent context or is a generic lambda (has
// template parameters) and has an 'auto' return type, deduce it to a
// dependent type.
if (Class->isDependentContext() || TemplateParams) {
const FunctionProtoType *FPT = MethodType->castAs<FunctionProtoType>();
QualType Result = FPT->getReturnType();
if (Result->isUndeducedType()) {
Result = SubstAutoType(Result, Context.DependentTy);
MethodType = Context.getFunctionType(Result, FPT->getParamTypes(),
// C++11 [expr.prim.lambda]p5:
// The closure type for a lambda-expression has a public inline function
// call operator (13.5.4) whose parameters and return type are described by
// the lambda-expression's parameter-declaration-clause and
// trailing-return-type respectively.
DeclarationName MethodName
= Context.DeclarationNames.getCXXOperatorName(OO_Call);
DeclarationNameLoc MethodNameLoc;
= IntroducerRange.getBegin().getRawEncoding();
= IntroducerRange.getEnd().getRawEncoding();
CXXMethodDecl *Method = CXXMethodDecl::Create(
Context, Class, EndLoc,
DeclarationNameInfo(MethodName, IntroducerRange.getBegin(),
MethodType, MethodTypeInfo, SC_None,
/*isInline=*/true, ConstexprKind, EndLoc);
if (!TemplateParams)
// Temporarily set the lexical declaration context to the current
// context, so that the Scope stack matches the lexical nesting.
// Create a function template if we have a template parameter list
FunctionTemplateDecl *const TemplateMethod = TemplateParams ?
FunctionTemplateDecl::Create(Context, Class,
Method->getLocation(), MethodName,
Method) : nullptr;
if (TemplateMethod) {
// Add parameters.
if (!Params.empty()) {
for (auto P : Method->parameters())
return Method;
void Sema::handleLambdaNumbering(
CXXRecordDecl *Class, CXXMethodDecl *Method,
Optional<std::tuple<unsigned, bool, Decl *>> Mangling) {
if (Mangling) {
unsigned ManglingNumber;
bool HasKnownInternalLinkage;
Decl *ManglingContextDecl;
std::tie(ManglingNumber, HasKnownInternalLinkage, ManglingContextDecl) =
Class->setLambdaMangling(ManglingNumber, ManglingContextDecl,
auto getMangleNumberingContext =
[this](CXXRecordDecl *Class, Decl *ManglingContextDecl) -> MangleNumberingContext * {
// Get mangle numbering context if there's any extra decl context.
if (ManglingContextDecl)
return &Context.getManglingNumberContext(
ASTContext::NeedExtraManglingDecl, ManglingContextDecl);
// Otherwise, from that lambda's decl context.
auto DC = Class->getDeclContext();
while (auto *CD = dyn_cast<CapturedDecl>(DC))
DC = CD->getParent();
return &Context.getManglingNumberContext(DC);
MangleNumberingContext *MCtx;
Decl *ManglingContextDecl;
std::tie(MCtx, ManglingContextDecl) =
bool HasKnownInternalLinkage = false;
if (!MCtx && getLangOpts().CUDA) {
// Force lambda numbering in CUDA/HIP as we need to name lambdas following
// ODR. Both device- and host-compilation need to have a consistent naming
// on kernel functions. As lambdas are potential part of these `__global__`
// function names, they needs numbering following ODR.
MCtx = getMangleNumberingContext(Class, ManglingContextDecl);
assert(MCtx && "Retrieving mangle numbering context failed!");
HasKnownInternalLinkage = true;
if (MCtx) {
unsigned ManglingNumber = MCtx->getManglingNumber(Method);
Class->setLambdaMangling(ManglingNumber, ManglingContextDecl,
void Sema::buildLambdaScope(LambdaScopeInfo *LSI,
CXXMethodDecl *CallOperator,
SourceRange IntroducerRange,
LambdaCaptureDefault CaptureDefault,
SourceLocation CaptureDefaultLoc,
bool ExplicitParams,
bool ExplicitResultType,
bool Mutable) {
LSI->CallOperator = CallOperator;
CXXRecordDecl *LambdaClass = CallOperator->getParent();
LSI->Lambda = LambdaClass;
if (CaptureDefault == LCD_ByCopy)
LSI->ImpCaptureStyle = LambdaScopeInfo::ImpCap_LambdaByval;
else if (CaptureDefault == LCD_ByRef)
LSI->ImpCaptureStyle = LambdaScopeInfo::ImpCap_LambdaByref;
LSI->CaptureDefaultLoc = CaptureDefaultLoc;
LSI->IntroducerRange = IntroducerRange;
LSI->ExplicitParams = ExplicitParams;
LSI->Mutable = Mutable;
if (ExplicitResultType) {
LSI->ReturnType = CallOperator->getReturnType();
if (!LSI->ReturnType->isDependentType() &&
!LSI->ReturnType->isVoidType()) {
if (RequireCompleteType(CallOperator->getBeginLoc(), LSI->ReturnType,
diag::err_lambda_incomplete_result)) {
// Do nothing.
} else {
LSI->HasImplicitReturnType = true;
void Sema::finishLambdaExplicitCaptures(LambdaScopeInfo *LSI) {
void Sema::ActOnLambdaExplicitTemplateParameterList(SourceLocation LAngleLoc,
ArrayRef<NamedDecl *> TParams,
SourceLocation RAngleLoc) {
LambdaScopeInfo *LSI = getCurLambda();
assert(LSI && "Expected a lambda scope");
assert(LSI->NumExplicitTemplateParams == 0 &&
"Already acted on explicit template parameters");
assert(LSI->TemplateParams.empty() &&
"Explicit template parameters should come "
"before invented (auto) ones");
assert(!TParams.empty() &&
"No template parameters to act on");
LSI->TemplateParams.append(TParams.begin(), TParams.end());
LSI->NumExplicitTemplateParams = TParams.size();
LSI->ExplicitTemplateParamsRange = {LAngleLoc, RAngleLoc};
void Sema::addLambdaParameters(
ArrayRef<LambdaIntroducer::LambdaCapture> Captures,
CXXMethodDecl *CallOperator, Scope *CurScope) {
// Introduce our parameters into the function scope
for (unsigned p = 0, NumParams = CallOperator->getNumParams();
p < NumParams; ++p) {
ParmVarDecl *Param = CallOperator->getParamDecl(p);
// If this has an identifier, add it to the scope stack.
if (CurScope && Param->getIdentifier()) {
bool Error = false;
// Resolution of CWG 2211 in C++17 renders shadowing ill-formed, but we
// retroactively apply it.
for (const auto &Capture : Captures) {
if (Capture.Id == Param->getIdentifier()) {
Error = true;
Diag(Param->getLocation(), diag::err_parameter_shadow_capture);
Diag(Capture.Loc, diag::note_var_explicitly_captured_here)
<< Capture.Id << true;
if (!Error)
CheckShadow(CurScope, Param);
PushOnScopeChains(Param, CurScope);
/// If this expression is an enumerator-like expression of some type
/// T, return the type T; otherwise, return null.
/// Pointer comparisons on the result here should always work because
/// it's derived from either the parent of an EnumConstantDecl
/// (i.e. the definition) or the declaration returned by
/// EnumType::getDecl() (i.e. the definition).
static EnumDecl *findEnumForBlockReturn(Expr *E) {
// An expression is an enumerator-like expression of type T if,
// ignoring parens and parens-like expressions:
E = E->IgnoreParens();
// - it is an enumerator whose enum type is T or
if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
if (EnumConstantDecl *D
= dyn_cast<EnumConstantDecl>(DRE->getDecl())) {
return cast<EnumDecl>(D->getDeclContext());
return nullptr;
// - it is a comma expression whose RHS is an enumerator-like
// expression of type T or
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
if (BO->getOpcode() == BO_Comma)
return findEnumForBlockReturn(BO->getRHS());
return nullptr;
// - it is a statement-expression whose value expression is an
// enumerator-like expression of type T or
if (StmtExpr *SE = dyn_cast<StmtExpr>(E)) {
if (Expr *last = dyn_cast_or_null<Expr>(SE->getSubStmt()->body_back()))
return findEnumForBlockReturn(last);
return nullptr;
// - it is a ternary conditional operator (not the GNU ?:
// extension) whose second and third operands are
// enumerator-like expressions of type T or
if (ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
if (EnumDecl *ED = findEnumForBlockReturn(CO->getTrueExpr()))
if (ED == findEnumForBlockReturn(CO->getFalseExpr()))
return ED;
return nullptr;
// (implicitly:)
// - it is an implicit integral conversion applied to an
// enumerator-like expression of type T or
if (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E)) {
// We can sometimes see integral conversions in valid
// enumerator-like expressions.
if (ICE->getCastKind() == CK_IntegralCast)
return findEnumForBlockReturn(ICE->getSubExpr());
// Otherwise, just rely on the type.
// - it is an expression of that formal enum type.
if (const EnumType *ET = E->getType()->getAs<EnumType>()) {
return ET->getDecl();
// Otherwise, nope.
return nullptr;
/// Attempt to find a type T for which the returned expression of the
/// given statement is an enumerator-like expression of that type.
static EnumDecl *findEnumForBlockReturn(ReturnStmt *ret) {
if (Expr *retValue = ret->getRetValue())
return findEnumForBlockReturn(retValue);
return nullptr;
/// Attempt to find a common type T for which all of the returned
/// expressions in a block are enumerator-like expressions of that
/// type.
static EnumDecl *findCommonEnumForBlockReturns(ArrayRef<ReturnStmt*> returns) {
ArrayRef<ReturnStmt*>::iterator i = returns.begin(), e = returns.end();
// Try to find one for the first return.
EnumDecl *ED = findEnumForBlockReturn(*i);
if (!ED) return nullptr;
// Check that the rest of the returns have the same enum.
for (++i; i != e; ++i) {
if (findEnumForBlockReturn(*i) != ED)
return nullptr;
// Never infer an anonymous enum type.
if (!ED->hasNameForLinkage()) return nullptr;
return ED;
/// Adjust the given return statements so that they formally return
/// the given type. It should require, at most, an IntegralCast.
static void adjustBlockReturnsToEnum(Sema &S, ArrayRef<ReturnStmt*> returns,
QualType returnType) {
for (ArrayRef<ReturnStmt*>::iterator
i = returns.begin(), e = returns.end(); i != e; ++i) {
ReturnStmt *ret = *i;
Expr *retValue = ret->getRetValue();
if (S.Context.hasSameType(retValue->getType(), returnType))
// Right now we only support integral fixup casts.
ExprWithCleanups *cleanups = dyn_cast<ExprWithCleanups>(retValue);
Expr *E = (cleanups ? cleanups->getSubExpr() : retValue);
E = ImplicitCastExpr::Create(S.Context, returnType, CK_IntegralCast,
E, /*base path*/ nullptr, VK_RValue);
if (cleanups) {
} else {
void Sema::deduceClosureReturnType(CapturingScopeInfo &CSI) {
// If it was ever a placeholder, it had to been deduced to DependentTy.
assert(CSI.ReturnType.isNull() || !CSI.ReturnType->isUndeducedType());
assert((!isa<LambdaScopeInfo>(CSI) || !getLangOpts().CPlusPlus14) &&
"lambda expressions use auto deduction in C++14 onwards");
// C++ core issue 975:
// If a lambda-expression does not include a trailing-return-type,
// it is as if the trailing-return-type denotes the following type:
// - if there are no return statements in the compound-statement,
// or all return statements return either an expression of type
// void or no expression or braced-init-list, the type void;
// - otherwise, if all return statements return an expression
// and the types of the returned expressions after
// lvalue-to-rvalue conversion (4.1 [conv.lval]),
// array-to-pointer conversion (4.2 [conv.array]), and
// function-to-pointer conversion (4.3 [conv.func]) are the
// same, that common type;
// - otherwise, the program is ill-formed.
// C++ core issue 1048 additionally removes top-level cv-qualifiers
// from the types of returned expressions to match the C++14 auto
// deduction rules.
// In addition, in blocks in non-C++ modes, if all of the return
// statements are enumerator-like expressions of some type T, where
// T has a name for linkage, then we infer the return type of the
// block to be that type.
// First case: no return statements, implicit void return type.
ASTContext &Ctx = getASTContext();
if (CSI.Returns.empty()) {
// It's possible there were simply no /valid/ return statements.
// In this case, the first one we found may have at least given us a type.
if (CSI.ReturnType.isNull())
CSI.ReturnType = Ctx.VoidTy;
// Second case: at least one return statement has dependent type.
// Delay type checking until instantiation.
assert(!CSI.ReturnType.isNull() && "We should have a tentative return type.");
if (CSI.ReturnType->isDependentType())
// Try to apply the enum-fuzz rule.
if (!getLangOpts().CPlusPlus) {
const EnumDecl *ED = findCommonEnumForBlockReturns(CSI.Returns);
if (ED) {
CSI.ReturnType = Context.getTypeDeclType(ED);
adjustBlockReturnsToEnum(*this, CSI.Returns, CSI.ReturnType);
// Third case: only one return statement. Don't bother doing extra work!
if (CSI.Returns.size() == 1)
// General case: many return statements.
// Check that they all have compatible return types.
// We require the return types to strictly match here.
// Note that we've already done the required promotions as part of
// processing the return statement.
for (const ReturnStmt *RS : CSI.Returns) {
const Expr *RetE = RS->getRetValue();
QualType ReturnType =
(RetE ? RetE->getType() : Context.VoidTy).getUnqualifiedType();
if (Context.getCanonicalFunctionResultType(ReturnType) ==
Context.getCanonicalFunctionResultType(CSI.ReturnType)) {
// Use the return type with the strictest possible nullability annotation.
auto RetTyNullability = ReturnType->getNullability(Ctx);
auto BlockNullability = CSI.ReturnType->getNullability(Ctx);
if (BlockNullability &&
(!RetTyNullability ||
hasWeakerNullability(*RetTyNullability, *BlockNullability)))
CSI.ReturnType = ReturnType;
// FIXME: This is a poor diagnostic for ReturnStmts without expressions.
// TODO: It's possible that the *first* return is the divergent one.
<< ReturnType << CSI.ReturnType << isa<LambdaScopeInfo>(CSI);
// Continue iterating so that we keep emitting diagnostics.
QualType Sema::buildLambdaInitCaptureInitialization(
SourceLocation Loc, bool ByRef, SourceLocation EllipsisLoc,
Optional<unsigned> NumExpansions, IdentifierInfo *Id, bool IsDirectInit,
Expr *&Init) {
// Create an 'auto' or 'auto&' TypeSourceInfo that we can use to
// deduce against.
QualType DeductType = Context.getAutoDeductType();
TypeLocBuilder TLB;
if (ByRef) {
DeductType = BuildReferenceType(DeductType, true, Loc, Id);
assert(!DeductType.isNull() && "can't build reference to auto");
if (EllipsisLoc.isValid()) {
if (Init->containsUnexpandedParameterPack()) {
Diag(EllipsisLoc, getLangOpts().CPlusPlus2a
? diag::warn_cxx17_compat_init_capture_pack
: diag::ext_init_capture_pack);
DeductType = Context.getPackExpansionType(DeductType, NumExpansions);
} else {
// Just ignore the ellipsis for now and form a non-pack variable. We'll
// diagnose this later when we try to capture it.
TypeSourceInfo *TSI = TLB.getTypeSourceInfo(Context, DeductType);
// Deduce the type of the init capture.
QualType DeducedType = deduceVarTypeFromInitializer(
/*VarDecl*/nullptr, DeclarationName(Id), DeductType, TSI,
SourceRange(Loc, Loc), IsDirectInit, Init);
if (DeducedType.isNull())
return QualType();
// Are we a non-list direct initialization?
ParenListExpr *CXXDirectInit = dyn_cast<ParenListExpr>(Init);
// Perform initialization analysis and ensure any implicit conversions
// (such as lvalue-to-rvalue) are enforced.
InitializedEntity Entity =
InitializedEntity::InitializeLambdaCapture(Id, DeducedType, Loc);
InitializationKind Kind =
? (CXXDirectInit ? InitializationKind::CreateDirect(
Loc, Init->getBeginLoc(), Init->getEndLoc())
: InitializationKind::CreateDirectList(Loc))
: InitializationKind::CreateCopy(Loc, Init->getBeginLoc());
MultiExprArg Args = Init;
if (CXXDirectInit)
Args =
MultiExprArg(CXXDirectInit->getExprs(), CXXDirectInit->getNumExprs());
QualType DclT;
InitializationSequence InitSeq(*this, Entity, Kind, Args);
ExprResult Result = InitSeq.Perform(*this, Entity, Kind, Args, &DclT);
if (Result.isInvalid())
return QualType();
Init = Result.getAs<Expr>();
return DeducedType;
VarDecl *Sema::createLambdaInitCaptureVarDecl(SourceLocation Loc,
QualType InitCaptureType,
SourceLocation EllipsisLoc,
IdentifierInfo *Id,
unsigned InitStyle, Expr *Init) {
// FIXME: Retain the TypeSourceInfo from buildLambdaInitCaptureInitialization
// rather than reconstructing it here.
TypeSourceInfo *TSI = Context.getTrivialTypeSourceInfo(InitCaptureType, Loc);
if (auto PETL = TSI->getTypeLoc().getAs<PackExpansionTypeLoc>())
// Create a dummy variable representing the init-capture. This is not actually
// used as a variable, and only exists as a way to name and refer to the
// init-capture.
// FIXME: Pass in separate source locations for '&' and identifier.
VarDecl *NewVD = VarDecl::Create(Context, CurContext, Loc,
Loc, Id, InitCaptureType, TSI, SC_Auto);
// FIXME: Pass in a VarDecl::InitializationStyle.
if (NewVD->isParameterPack())
return NewVD;
void Sema::addInitCapture(LambdaScopeInfo *LSI, VarDecl *Var) {
assert(Var->isInitCapture() && "init capture flag should be set");
LSI->addCapture(Var, /*isBlock*/false, Var->getType()->isReferenceType(),
/*isNested*/false, Var->getLocation(), SourceLocation(),
Var->getType(), /*Invalid*/false);
void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
Declarator &ParamInfo,
Scope *CurScope) {
LambdaScopeInfo *const LSI = getCurLambda();
assert(LSI && "LambdaScopeInfo should be on stack!");
// Determine if we're within a context where we know that the lambda will
// be dependent, because there are template parameters in scope.
bool KnownDependent;
if (LSI->NumExplicitTemplateParams > 0) {
auto *TemplateParamScope = CurScope->getTemplateParamParent();
assert(TemplateParamScope &&
"Lambda with explicit template param list should establish a "
"template param scope");
KnownDependent = TemplateParamScope->getParent()
->getTemplateParamParent() != nullptr;
} else {
KnownDependent = CurScope->getTemplateParamParent() != nullptr;
// Determine the signature of the call operator.
TypeSourceInfo *MethodTyInfo;
bool ExplicitParams = true;
bool ExplicitResultType = true;
bool ContainsUnexpandedParameterPack = false;
SourceLocation EndLoc;
SmallVector<ParmVarDecl *, 8> Params;
if (ParamInfo.getNumTypeObjects() == 0) {
// C++11 [expr.prim.lambda]p4:
// If a lambda-expression does not include a lambda-declarator, it is as
// if the lambda-declarator were ().
FunctionProtoType::ExtProtoInfo EPI(Context.getDefaultCallingConvention(
/*IsVariadic=*/false, /*IsCXXMethod=*/true));
EPI.HasTrailingReturn = true;
// C++1y [expr.prim.lambda]:
// The lambda return type is 'auto', which is replaced by the
// trailing-return type if provided and/or deduced from 'return'
// statements
// We don't do this before C++1y, because we don't support deduced return
// types there.
QualType DefaultTypeForNoTrailingReturn =
getLangOpts().CPlusPlus14 ? Context.getAutoDeductType()
: Context.DependentTy;
QualType MethodTy =
Context.getFunctionType(DefaultTypeForNoTrailingReturn, None, EPI);
MethodTyInfo = Context.getTrivialTypeSourceInfo(MethodTy);
ExplicitParams = false;
ExplicitResultType = false;
EndLoc = Intro.Range.getEnd();
} else {
assert(ParamInfo.isFunctionDeclarator() &&
"lambda-declarator is a function");
DeclaratorChunk::FunctionTypeInfo &FTI = ParamInfo.getFunctionTypeInfo();
// C++11 [expr.prim.lambda]p5:
// This function call operator is declared const (9.3.1) if and only if
// the lambda-expression's parameter-declaration-clause is not followed
// by mutable. It is neither virtual nor declared volatile. [...]
if (!FTI.hasMutableQualifier()) {
MethodTyInfo = GetTypeForDeclarator(ParamInfo, CurScope);
assert(MethodTyInfo && "no type from lambda-declarator");
EndLoc = ParamInfo.getSourceRange().getEnd();
ExplicitResultType = FTI.hasTrailingReturnType();
if (FTIHasNonVoidParameters(FTI)) {
for (unsigned i = 0, e = FTI.NumParams; i != e; ++i)
// Check for unexpanded parameter packs in the method type.
if (MethodTyInfo->getType()->containsUnexpandedParameterPack())
DiagnoseUnexpandedParameterPack(Intro.Range.getBegin(), MethodTyInfo,
CXXRecordDecl *Class = createLambdaClosureType(Intro.Range, MethodTyInfo,
KnownDependent, Intro.Default);
CXXMethodDecl *Method =
startLambdaDefinition(Class, Intro.Range, MethodTyInfo, EndLoc, Params,
if (ExplicitParams)
// This represents the function body for the lambda function, check if we
// have to apply optnone due to a pragma.
// code_seg attribute on lambda apply to the method.
if (Attr *A = getImplicitCodeSegOrSectionAttrForFunction(Method, /*IsDefinition=*/true))
// Attributes on the lambda apply to the method.
ProcessDeclAttributes(CurScope, Method, ParamInfo);
// CUDA lambdas get implicit attributes based on the scope in which they're
// declared.
if (getLangOpts().CUDA)
// Number the lambda for linkage purposes if necessary.
handleLambdaNumbering(Class, Method);
// Introduce the function call operator as the current declaration context.
PushDeclContext(CurScope, Method);
// Build the lambda scope.
buildLambdaScope(LSI, Method, Intro.Range, Intro.Default, Intro.DefaultLoc,
ExplicitParams, ExplicitResultType, !Method->isConst());
// C++11 [expr.prim.lambda]p9:
// A lambda-expression whose smallest enclosing scope is a block scope is a
// local lambda expression; any other lambda expression shall not have a
// capture-default or simple-capture in its lambda-introducer.
// For simple-captures, this is covered by the check below that any named
// entity is a variable that can be captured.
// For DR1632, we also allow a capture-default in any context where we can
// odr-use 'this' (in particular, in a default initializer for a non-static
// data member).
if (Intro.Default != LCD_None && !Class->getParent()->isFunctionOrMethod() &&
(getCurrentThisType().isNull() ||
CheckCXXThisCapture(SourceLocation(), /*Explicit*/true,
Diag(Intro.DefaultLoc, diag::err_capture_default_non_local);
// Distinct capture names, for diagnostics.
llvm::SmallSet<IdentifierInfo*, 8> CaptureNames;
// Handle explicit captures.
SourceLocation PrevCaptureLoc
= Intro.Default == LCD_None? Intro.Range.getBegin() : Intro.DefaultLoc;
for (auto C = Intro.Captures.begin(), E = Intro.Captures.end(); C != E;
PrevCaptureLoc = C->Loc, ++C) {
if (C->Kind == LCK_This || C->Kind == LCK_StarThis) {
if (C->Kind == LCK_StarThis)
Diag(C->Loc, !getLangOpts().CPlusPlus17
? diag::ext_star_this_lambda_capture_cxx17
: diag::warn_cxx14_compat_star_this_lambda_capture);
// C++11 [expr.prim.lambda]p8:
// An identifier or this shall not appear more than once in a
// lambda-capture.
if (LSI->isCXXThisCaptured()) {
Diag(C->Loc, diag::err_capture_more_than_once)
<< "'this'" << SourceRange(LSI->getCXXThisCapture().getLocation())
<< FixItHint::CreateRemoval(
SourceRange(getLocForEndOfToken(PrevCaptureLoc), C->Loc));
// C++2a [expr.prim.lambda]p8:
// If a lambda-capture includes a capture-default that is =,
// each simple-capture of that lambda-capture shall be of the form
// "&identifier", "this", or "* this". [ Note: The form [&,this] is
// redundant but accepted for compatibility with ISO C++14. --end note ]
if (Intro.Default == LCD_ByCopy && C->Kind != LCK_StarThis)
Diag(C->Loc, !getLangOpts().CPlusPlus2a
? diag::ext_equals_this_lambda_capture_cxx2a
: diag::warn_cxx17_compat_equals_this_lambda_capture);
// C++11 [expr.prim.lambda]p12:
// If this is captured by a local lambda expression, its nearest
// enclosing function shall be a non-static member function.
QualType ThisCaptureType = getCurrentThisType();
if (ThisCaptureType.isNull()) {
Diag(C->Loc, diag::err_this_capture) << true;
CheckCXXThisCapture(C->Loc, /*Explicit=*/true, /*BuildAndDiagnose*/ true,
/*FunctionScopeIndexToStopAtPtr*/ nullptr,
C->Kind == LCK_StarThis);
if (!LSI->Captures.empty())
LSI->ExplicitCaptureRanges[LSI->Captures.size() - 1] = C->ExplicitRange;
assert(C->Id && "missing identifier for capture");
if (C->Init.isInvalid())
VarDecl *Var = nullptr;
if (C->Init.isUsable()) {
Diag(C->Loc, getLangOpts().CPlusPlus14
? diag::warn_cxx11_compat_init_capture
: diag::ext_init_capture);
// If the initializer expression is usable, but the InitCaptureType
// is not, then an error has occurred - so ignore the capture for now.
// for e.g., [n{0}] { }; <-- if no <initializer_list> is included.
// FIXME: we should create the init capture variable and mark it invalid
// in this case.
if (C->InitCaptureType.get().isNull())
if (C->Init.get()->containsUnexpandedParameterPack() &&
DiagnoseUnexpandedParameterPack(C->Init.get(), UPPC_Initializer);
unsigned InitStyle;
switch (C->InitKind) {
case LambdaCaptureInitKind::NoInit:
llvm_unreachable("not an init-capture?");
case LambdaCaptureInitKind::CopyInit:
InitStyle = VarDecl::CInit;
case LambdaCaptureInitKind::DirectInit:
InitStyle = VarDecl::CallInit;
case LambdaCaptureInitKind::ListInit:
InitStyle = VarDecl::ListInit;
Var = createLambdaInitCaptureVarDecl(C->Loc, C->InitCaptureType.get(),
C->EllipsisLoc, C->Id, InitStyle,
// C++1y [expr.prim.lambda]p11:
// An init-capture behaves as if it declares and explicitly
// captures a variable [...] whose declarative region is the
// lambda-expression's compound-statement
if (Var)
PushOnScopeChains(Var, CurScope, false);
} else {
assert(C->InitKind == LambdaCaptureInitKind::NoInit &&
"init capture has valid but null init?");
// C++11 [expr.prim.lambda]p8:
// If a lambda-capture includes a capture-default that is &, the
// identifiers in the lambda-capture shall not be preceded by &.
// If a lambda-capture includes a capture-default that is =, [...]
// each identifier it contains shall be preceded by &.
if (C->Kind == LCK_ByRef && Intro.Default == LCD_ByRef) {
Diag(C->Loc, diag::err_reference_capture_with_reference_default)
<< FixItHint::CreateRemoval(
SourceRange(getLocForEndOfToken(PrevCaptureLoc), C->Loc));
} else if (C->Kind == LCK_ByCopy && Intro.Default == LCD_ByCopy) {
Diag(C->Loc, diag::err_copy_capture_with_copy_default)
<< FixItHint::CreateRemoval(
SourceRange(getLocForEndOfToken(PrevCaptureLoc), C->Loc));
// C++11 [expr.prim.lambda]p10:
// The identifiers in a capture-list are looked up using the usual
// rules for unqualified name lookup (3.4.1)
DeclarationNameInfo Name(C->Id, C->Loc);
LookupResult R(*this, Name, LookupOrdinaryName);
LookupName(R, CurScope);
if (R.isAmbiguous())
if (R.empty()) {
// FIXME: Disable corrections that would add qualification?
CXXScopeSpec ScopeSpec;
DeclFilterCCC<VarDecl> Validator{};
if (DiagnoseEmptyLookup(CurScope, ScopeSpec, R, Validator))
Var = R.getAsSingle<VarDecl>();
if (Var && DiagnoseUseOfDecl(Var, C->Loc))
// C++11 [expr.prim.lambda]p8:
// An identifier or this shall not appear more than once in a
// lambda-capture.
if (!CaptureNames.insert(C->Id).second) {
if (Var && LSI->isCaptured(Var)) {
Diag(C->Loc, diag::err_capture_more_than_once)
<< C->Id << SourceRange(LSI->getCapture(Var).getLocation())
<< FixItHint::CreateRemoval(
SourceRange(getLocForEndOfToken(PrevCaptureLoc), C->Loc));
} else
// Previous capture captured something different (one or both was
// an init-cpature): no fixit.
Diag(C->Loc, diag::err_capture_more_than_once) << C->Id;
// C++11 [expr.prim.lambda]p10:
// [...] each such lookup shall find a variable with automatic storage
// duration declared in the reaching scope of the local lambda expression.
// Note that the 'reaching scope' check happens in tryCaptureVariable().
if (!Var) {
Diag(C->Loc, diag::err_capture_does_not_name_variable) << C->Id;
// Ignore invalid decls; they'll just confuse the code later.
if (Var->isInvalidDecl())
if (!Var->hasLocalStorage()) {
Diag(C->Loc, diag::err_capture_non_automatic_variable) << C->Id;
Diag(Var->getLocation(), diag::note_previous_decl) << C->Id;
// C++11 [expr.prim.lambda]p23:
// A capture followed by an ellipsis is a pack expansion (14.5.3).
SourceLocation EllipsisLoc;
if (C->EllipsisLoc.isValid()) {
if (Var->isParameterPack()) {
EllipsisLoc = C->EllipsisLoc;
} else {
Diag(C->EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
<< (C->Init.isUsable() ? C->Init.get()->getSourceRange()
: SourceRange(C->Loc));
// Just ignore the ellipsis.
} else if (Var->isParameterPack()) {
ContainsUnexpandedParameterPack = true;
if (C->Init.isUsable()) {
addInitCapture(LSI, Var);
} else {
TryCaptureKind Kind = C->Kind == LCK_ByRef ? TryCapture_ExplicitByRef :
tryCaptureVariable(Var, C->Loc, Kind, EllipsisLoc);
if (!LSI->Captures.empty())
LSI->ExplicitCaptureRanges[LSI->Captures.size() - 1] = C->ExplicitRange;
LSI->ContainsUnexpandedParameterPack |= ContainsUnexpandedParameterPack;
// Add lambda parameters into scope.
addLambdaParameters(Intro.Captures, Method, CurScope);
// Enter a new evaluation context to insulate the lambda from any
// cleanups from the enclosing full-expression.
void Sema::ActOnLambdaError(SourceLocation StartLoc, Scope *CurScope,
bool IsInstantiation) {
LambdaScopeInfo *LSI = cast<LambdaScopeInfo>(FunctionScopes.back());
// Leave the expression-evaluation context.
// Leave the context of the lambda.
if (!IsInstantiation)
// Finalize the lambda.
CXXRecordDecl *Class = LSI->Lambda;
SmallVector<Decl*, 4> Fields(Class->fields());
ActOnFields(nullptr, Class->getLocation(), Class, Fields, SourceLocation(),
SourceLocation(), ParsedAttributesView());
QualType Sema::getLambdaConversionFunctionResultType(
const FunctionProtoType *CallOpProto) {
// The function type inside the pointer type is the same as the call
// operator with some tweaks. The calling convention is the default free
// function convention, and the type qualifications are lost.
const FunctionProtoType::ExtProtoInfo CallOpExtInfo =
FunctionProtoType::ExtProtoInfo InvokerExtInfo = CallOpExtInfo;
CallingConv CC = Context.getDefaultCallingConvention(
CallOpProto->isVariadic(), /*IsCXXMethod=*/false);
InvokerExtInfo.ExtInfo = InvokerExtInfo.ExtInfo.withCallingConv(CC);
InvokerExtInfo.TypeQuals = Qualifiers();
assert(InvokerExtInfo.RefQualifier == RQ_None &&
"Lambda's call operator should not have a reference qualifier");
return Context.getFunctionType(CallOpProto->getReturnType(),
CallOpProto->getParamTypes(), InvokerExtInfo);
/// Add a lambda's conversion to function pointer, as described in
/// C++11 [expr.prim.lambda]p6.
static void addFunctionPointerConversion(Sema &S,
SourceRange IntroducerRange,
CXXRecordDecl *Class,
CXXMethodDecl *CallOperator) {
// This conversion is explicitly disabled if the lambda's function has
// pass_object_size attributes on any of its parameters.
auto HasPassObjectSizeAttr = [](const ParmVarDecl *P) {
return P->hasAttr<PassObjectSizeAttr>();
if (llvm::any_of(CallOperator->parameters(), HasPassObjectSizeAttr))
// Add the conversion to function pointer.
QualType InvokerFunctionTy = S.getLambdaConversionFunctionResultType(
QualType PtrToFunctionTy = S.Context.getPointerType(InvokerFunctionTy);
// Create the type of the conversion function.
FunctionProtoType::ExtProtoInfo ConvExtInfo(
/*IsVariadic=*/false, /*IsCXXMethod=*/true));
// The conversion function is always const and noexcept.
ConvExtInfo.TypeQuals = Qualifiers();
ConvExtInfo.ExceptionSpec.Type = EST_BasicNoexcept;
QualType ConvTy =
S.Context.getFunctionType(PtrToFunctionTy, None, ConvExtInfo);
SourceLocation Loc = IntroducerRange.getBegin();
DeclarationName ConversionName
= S.Context.DeclarationNames.getCXXConversionFunctionName(
DeclarationNameLoc ConvNameLoc;
// Construct a TypeSourceInfo for the conversion function, and wire
// all the parameters appropriately for the FunctionProtoTypeLoc
// so that everything works during transformation/instantiation of
// generic lambdas.
// The main reason for wiring up the parameters of the conversion
// function with that of the call operator is so that constructs
// like the following work:
// auto L = [](auto b) { <-- 1
// return [](auto a) -> decltype(a) { <-- 2
// return a;
// };
// };
// int (*fp)(int) = L(5);
// Because the trailing return type can contain DeclRefExprs that refer
// to the original call operator's variables, we hijack the call
// operators ParmVarDecls below.
TypeSourceInfo *ConvNamePtrToFunctionTSI =
S.Context.getTrivialTypeSourceInfo(PtrToFunctionTy, Loc);
ConvNameLoc.NamedType.TInfo = ConvNamePtrToFunctionTSI;
// The conversion function is a conversion to a pointer-to-function.
TypeSourceInfo *ConvTSI = S.Context.getTrivialTypeSourceInfo(ConvTy, Loc);
FunctionProtoTypeLoc ConvTL =
// Get the result of the conversion function which is a pointer-to-function.
PointerTypeLoc PtrToFunctionTL =
// Do the same for the TypeSourceInfo that is used to name the conversion
// operator.
PointerTypeLoc ConvNamePtrToFunctionTL =
// Get the underlying function types that the conversion function will
// be converting to (should match the type of the call operator).
FunctionProtoTypeLoc CallOpConvTL =
FunctionProtoTypeLoc CallOpConvNameTL =
// Wire up the FunctionProtoTypeLocs with the call operator's parameters.
// These parameter's are essentially used to transform the name and
// the type of the conversion operator. By using the same parameters
// as the call operator's we don't have to fix any back references that
// the trailing return type of the call operator's uses (such as
// decltype(some_type<decltype(a)>::type{} + decltype(a){}) etc.)
// - we can simply use the return type of the call operator, and
// everything should work.
SmallVector<ParmVarDecl *, 4> InvokerParams;
for (unsigned I = 0, N = CallOperator->getNumParams(); I != N; ++I) {
ParmVarDecl *From = CallOperator->getParamDecl(I);
// Temporarily add to the TU. This is set to the invoker below.
S.Context.getTranslationUnitDecl(), From->getBeginLoc(),
From->getLocation(), From->getIdentifier(), From->getType(),
From->getTypeSourceInfo(), From->getStorageClass(),
CallOpConvTL.setParam(I, From);
CallOpConvNameTL.setParam(I, From);
CXXConversionDecl *Conversion = CXXConversionDecl::Create(
S.Context, Class, Loc,
DeclarationNameInfo(ConversionName, Loc, ConvNameLoc), ConvTy, ConvTSI,
/*isInline=*/true, ExplicitSpecifier(),
S.getLangOpts().CPlusPlus17 ? CSK_constexpr : CSK_unspecified,
if (Class->isGenericLambda()) {
// Create a template version of the conversion operator, using the template
// parameter list of the function call operator.
FunctionTemplateDecl *TemplateCallOperator =
FunctionTemplateDecl *ConversionTemplate =
FunctionTemplateDecl::Create(S.Context, Class,
Loc, ConversionName,
} else
// Add a non-static member function that will be the result of
// the conversion with a certain unique ID.
DeclarationName InvokerName = &S.Context.Idents.get(
// FIXME: Instead of passing in the CallOperator->getTypeSourceInfo()
// we should get a prebuilt TrivialTypeSourceInfo from Context
// using FunctionTy & Loc and get its TypeLoc as a FunctionProtoTypeLoc
// then rewire the parameters accordingly, by hoisting up the InvokeParams
// loop below and then use its Params to set Invoke->setParams(...) below.
// This would avoid the 'const' qualifier of the calloperator from
// contaminating the type of the invoker, which is currently adjusted
// in SemaTemplateDeduction.cpp:DeduceTemplateArguments. Fixing the
// trailing return type of the invoker would require a visitor to rebuild
// the trailing return type and adjusting all back DeclRefExpr's to refer
// to the new static invoker parameters - not the call operator's.
CXXMethodDecl *Invoke = CXXMethodDecl::Create(
S.Context, Class, Loc, DeclarationNameInfo(InvokerName, Loc),
InvokerFunctionTy, CallOperator->getTypeSourceInfo(), SC_Static,
/*isInline=*/true, CSK_unspecified, CallOperator->getBody()->getEndLoc());
for (unsigned I = 0, N = CallOperator->getNumParams(); I != N; ++I)
if (Class->isGenericLambda()) {
FunctionTemplateDecl *TemplateCallOperator =
FunctionTemplateDecl *StaticInvokerTemplate = FunctionTemplateDecl::Create(
S.Context, Class, Loc, InvokerName,
} else
/// Add a lambda's conversion to block pointer.
static void addBlockPointerConversion(Sema &S,
SourceRange IntroducerRange,
CXXRecordDecl *Class,
CXXMethodDecl *CallOperator) {
QualType FunctionTy = S.getLambdaConversionFunctionResultType(
QualType BlockPtrTy = S.Context.getBlockPointerType(FunctionTy);
FunctionProtoType::ExtProtoInfo ConversionEPI(
/*IsVariadic=*/false, /*IsCXXMethod=*/true));
ConversionEPI.TypeQuals = Qualifiers();
QualType ConvTy = S.Context.getFunctionType(BlockPtrTy, None, ConversionEPI);
SourceLocation Loc = IntroducerRange.getBegin();
DeclarationName Name
= S.Context.DeclarationNames.getCXXConversionFunctionName(
DeclarationNameLoc NameLoc;
NameLoc.NamedType.TInfo = S.Context.getTrivialTypeSourceInfo(BlockPtrTy, Loc);
CXXConversionDecl *Conversion = CXXConversionDecl::Create(
S.Context, Class, Loc, DeclarationNameInfo(Name, Loc, NameLoc), ConvTy,
S.Context.getTrivialTypeSourceInfo(ConvTy, Loc),
/*isInline=*/true, ExplicitSpecifier(), CSK_unspecified,
ExprResult Sema::BuildCaptureInit(const Capture &Cap,
SourceLocation ImplicitCaptureLoc,
bool IsOpenMPMapping) {
// VLA captures don't have a stored initialization expression.
if (Cap.isVLATypeCapture())
return ExprResult();
// An init-capture is initialized directly from its stored initializer.
if (Cap.isInitCapture())
return Cap.getVariable()->getInit();
// For anything else, build an initialization expression. For an implicit
// capture, the capture notionally happens at the capture-default, so use
// that location here.
SourceLocation Loc =
ImplicitCaptureLoc.isValid() ? ImplicitCaptureLoc : Cap.getLocation();
// C++11 [expr.prim.lambda]p21:
// When the lambda-expression is evaluated, the entities that
// are captured by copy are used to direct-initialize each
// corresponding non-static data member of the resulting closure
// object. (For array members, the array elements are
// direct-initialized in increasing subscript order.) These
// initializations are performed in the (unspecified) order in
// which the non-static data members are declared.
// C++ [expr.prim.lambda]p12:
// An entity captured by a lambda-expression is odr-used (3.2) in
// the scope containing the lambda-expression.
ExprResult Init;
IdentifierInfo *Name = nullptr;
if (Cap.isThisCapture()) {
QualType ThisTy = getCurrentThisType();
Expr *This = BuildCXXThisExpr(Loc, ThisTy, ImplicitCaptureLoc.isValid());
if (Cap.isCopyCapture())
Init = CreateBuiltinUnaryOp(Loc, UO_Deref, This);
Init = This;
} else {
assert(Cap.isVariableCapture() && "unknown kind of capture");
VarDecl *Var = Cap.getVariable();
Name = Var->getIdentifier();
Init = BuildDeclarationNameExpr(
CXXScopeSpec(), DeclarationNameInfo(Var->getDeclName(), Loc), Var);
// In OpenMP, the capture kind doesn't actually describe how to capture:
// variables are "mapped" onto the device in a process that does not formally
// make a copy, even for a "copy capture".
if (IsOpenMPMapping)
return Init;
if (Init.isInvalid())
return ExprError();
Expr *InitExpr = Init.get();
InitializedEntity Entity = InitializedEntity::InitializeLambdaCapture(
Name, Cap.getCaptureType(), Loc);
InitializationKind InitKind =
InitializationKind::CreateDirect(Loc, Loc, Loc);
InitializationSequence InitSeq(*this, Entity, InitKind, InitExpr);
return InitSeq.Perform(*this, Entity, InitKind, InitExpr);
ExprResult Sema::ActOnLambdaExpr(SourceLocation StartLoc, Stmt *Body,
Scope *CurScope) {
LambdaScopeInfo LSI = *cast<LambdaScopeInfo>(FunctionScopes.back());
ActOnFinishFunctionBody(LSI.CallOperator, Body);
return BuildLambdaExpr(StartLoc, Body->getEndLoc(), &LSI);
static LambdaCaptureDefault
mapImplicitCaptureStyle(CapturingScopeInfo::ImplicitCaptureStyle ICS) {
switch (ICS) {
case CapturingScopeInfo::ImpCap_None:
return LCD_None;
case CapturingScopeInfo::ImpCap_LambdaByval:
return LCD_ByCopy;
case CapturingScopeInfo::ImpCap_CapturedRegion:
case CapturingScopeInfo::ImpCap_LambdaByref:
return LCD_ByRef;
case CapturingScopeInfo::ImpCap_Block:
llvm_unreachable("block capture in lambda");
llvm_unreachable("Unknown implicit capture style");
bool Sema::CaptureHasSideEffects(const Capture &From) {
if (From.isInitCapture()) {
Expr *Init = From.getVariable()->getInit();
if (Init && Init->HasSideEffects(Context))
return true;
if (!From.isCopyCapture())
return false;
const QualType T = From.isThisCapture()
? getCurrentThisType()->getPointeeType()
: From.getCaptureType();
if (T.isVolatileQualified())
return true;
const Type *BaseT = T->getBaseElementTypeUnsafe();
if (const CXXRecordDecl *RD = BaseT->getAsCXXRecordDecl())
return !RD->isCompleteDefinition() || !RD->hasTrivialCopyConstructor() ||
return false;
bool Sema::DiagnoseUnusedLambdaCapture(SourceRange CaptureRange,
const Capture &From) {
if (CaptureHasSideEffects(From))
return false;
if (From.isVLATypeCapture())
return false;
auto diag = Diag(From.getLocation(), diag::warn_unused_lambda_capture);
if (From.isThisCapture())
diag << "'this'";
diag << From.getVariable();
diag << From.isNonODRUsed();
diag << FixItHint::CreateRemoval(CaptureRange);
return true;
/// Create a field within the lambda class or captured statement record for the
/// given capture.
FieldDecl *Sema::BuildCaptureField(RecordDecl *RD,
const sema::Capture &Capture) {
SourceLocation Loc = Capture.getLocation();
QualType FieldType = Capture.getCaptureType();
TypeSourceInfo *TSI = nullptr;
if (Capture.isVariableCapture()) {
auto *Var = Capture.getVariable();
if (Var->isInitCapture())
TSI = Capture.getVariable()->getTypeSourceInfo();
// FIXME: Should we really be doing this? A null TypeSourceInfo seems more
// appropriate, at least for an implicit capture.
if (!TSI)
TSI = Context.getTrivialTypeSourceInfo(FieldType, Loc);
// Build the non-static data member.
FieldDecl *Field =
FieldDecl::Create(Context, RD, Loc, Loc, nullptr, FieldType, TSI, nullptr,
false, ICIS_NoInit);
// If the variable being captured has an invalid type, mark the class as
// invalid as well.
if (!FieldType->isDependentType()) {
if (RequireCompleteType(Loc, FieldType, diag::err_field_incomplete)) {
} else {
NamedDecl *Def;
if (Def && Def->isInvalidDecl()) {
if (Capture.isVLATypeCapture())
return Field;
ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
LambdaScopeInfo *LSI) {
// Collect information from the lambda scope.
SmallVector<LambdaCapture, 4> Captures;
SmallVector<Expr *, 4> CaptureInits;
SourceLocation CaptureDefaultLoc = LSI->CaptureDefaultLoc;
LambdaCaptureDefault CaptureDefault =
CXXRecordDecl *Class;
CXXMethodDecl *CallOperator;
SourceRange IntroducerRange;
bool ExplicitParams;
bool ExplicitResultType;
CleanupInfo LambdaCleanup;
bool ContainsUnexpandedParameterPack;
bool IsGenericLambda;
CallOperator = LSI->CallOperator;
Class = LSI->Lambda;
IntroducerRange = LSI->IntroducerRange;
ExplicitParams = LSI->ExplicitParams;
ExplicitResultType = !LSI->HasImplicitReturnType;
LambdaCleanup = LSI->Cleanup;
ContainsUnexpandedParameterPack = LSI->ContainsUnexpandedParameterPack;
IsGenericLambda = Class->isGenericLambda();
Decl *TemplateOrNonTemplateCallOperatorDecl =
? CallOperator->getDescribedFunctionTemplate()
: cast<Decl>(CallOperator);
// FIXME: Is this really the best choice? Keeping the lexical decl context
// set as CurContext seems more faithful to the source.
// True if the current capture has a used capture or default before it.
bool CurHasPreviousCapture = CaptureDefault != LCD_None;
SourceLocation PrevCaptureLoc = CurHasPreviousCapture ?
CaptureDefaultLoc : IntroducerRange.getBegin();
for (unsigned I = 0, N = LSI->Captures.size(); I != N; ++I) {
const Capture &From = LSI->Captures[I];
if (From.isInvalid())
return ExprError();
assert(!From.isBlockCapture() && "Cannot capture __block variables");
bool IsImplicit = I >= LSI->NumExplicitCaptures;
SourceLocation ImplicitCaptureLoc =
IsImplicit ? CaptureDefaultLoc : SourceLocation();
// Use source ranges of explicit captures for fixits where available.
SourceRange CaptureRange = LSI->ExplicitCaptureRanges[I];
// Warn about unused explicit captures.
bool IsCaptureUsed = true;
if (!CurContext->isDependentContext() && !IsImplicit &&
!From.isODRUsed()) {
// Initialized captures that are non-ODR used may not be eliminated.
// FIXME: Where did the IsGenericLambda here come from?
bool NonODRUsedInitCapture =
IsGenericLambda && From.isNonODRUsed() && From.isInitCapture();
if (!NonODRUsedInitCapture) {
bool IsLast = (I + 1) == LSI->NumExplicitCaptures;
SourceRange FixItRange;
if (CaptureRange.isValid()) {
if (!CurHasPreviousCapture && !IsLast) {
// If there are no captures preceding this capture, remove the
// following comma.
FixItRange = SourceRange(CaptureRange.getBegin(),
} else {
// Otherwise, remove the comma since the last used capture.
FixItRange = SourceRange(getLocForEndOfToken(PrevCaptureLoc),
IsCaptureUsed = !DiagnoseUnusedLambdaCapture(FixItRange, From);
if (CaptureRange.isValid()) {
CurHasPreviousCapture |= IsCaptureUsed;
PrevCaptureLoc = CaptureRange.getEnd();
// Map the capture to our AST representation.
LambdaCapture Capture = [&] {
if (From.isThisCapture()) {
// Capturing 'this' implicitly with a default of '[=]' is deprecated,
// because it results in a reference capture. Don't warn prior to
// C++2a; there's nothing that can be done about it before then.
if (getLangOpts().CPlusPlus2a && IsImplicit &&
CaptureDefault == LCD_ByCopy) {
Diag(From.getLocation(), diag::warn_deprecated_this_capture);
Diag(CaptureDefaultLoc, diag::note_deprecated_this_capture)
<< FixItHint::CreateInsertion(
getLocForEndOfToken(CaptureDefaultLoc), ", this");
return LambdaCapture(From.getLocation(), IsImplicit,
From.isCopyCapture() ? LCK_StarThis : LCK_This);
} else if (From.isVLATypeCapture()) {
return LambdaCapture(From.getLocation(), IsImplicit, LCK_VLAType);
} else {
assert(From.isVariableCapture() && "unknown kind of capture");
VarDecl *Var = From.getVariable();
LambdaCaptureKind Kind =
From.isCopyCapture() ? LCK_ByCopy : LCK_ByRef;
return LambdaCapture(From.getLocation(), IsImplicit, Kind, Var,
// Form the initializer for the capture field.
ExprResult Init = BuildCaptureInit(From, ImplicitCaptureLoc);
// FIXME: Skip this capture if the capture is not used, the initializer
// has no side-effects, the type of the capture is trivial, and the
// lambda is not externally visible.
// Add a FieldDecl for the capture and form its initializer.
BuildCaptureField(Class, From);
// C++11 [expr.prim.lambda]p6:
// The closure type for a lambda-expression with no lambda-capture
// has a public non-virtual non-explicit const conversion function
// to pointer to function having the same parameter and return
// types as the closure type's function call operator.
if (Captures.empty() && CaptureDefault == LCD_None)
addFunctionPointerConversion(*this, IntroducerRange, Class,
// Objective-C++:
// The closure type for a lambda-expression has a public non-virtual
// non-explicit const conversion function to a block pointer having the
// same parameter and return types as the closure type's function call
// operator.
// FIXME: Fix generic lambda to block conversions.
if (getLangOpts().Blocks && getLangOpts().ObjC && !IsGenericLambda)
addBlockPointerConversion(*this, IntroducerRange, Class, CallOperator);
// Finalize the lambda class.
SmallVector<Decl*, 4> Fields(Class->fields());
ActOnFields(nullptr, Class->getLocation(), Class, Fields, SourceLocation(),
SourceLocation(), ParsedAttributesView());
LambdaExpr *Lambda = LambdaExpr::Create(Context, Class, IntroducerRange,
CaptureDefault, CaptureDefaultLoc,
ExplicitParams, ExplicitResultType,
CaptureInits, EndLoc,
// If the lambda expression's call operator is not explicitly marked constexpr
// and we are not in a dependent context, analyze the call operator to infer
// its constexpr-ness, suppressing diagnostics while doing so.
if (getLangOpts().CPlusPlus17 && !CallOperator->isInvalidDecl() &&
!CallOperator->isConstexpr() &&
!isa<CoroutineBodyStmt>(CallOperator->getBody()) &&
!Class->getDeclContext()->isDependentContext()) {
? CSK_constexpr
: CSK_unspecified);
// Emit delayed shadowing warnings now that the full capture list is known.
if (!CurContext->isDependentContext()) {
switch (ExprEvalContexts.back().Context) {
// C++11 [expr.prim.lambda]p2:
// A lambda-expression shall not appear in an unevaluated operand
// (Clause 5).
case ExpressionEvaluationContext::Unevaluated:
case ExpressionEvaluationContext::UnevaluatedList:
case ExpressionEvaluationContext::UnevaluatedAbstract:
// C++1y [expr.const]p2:
// A conditional-expression e is a core constant expression unless the
// evaluation of e, following the rules of the abstract machine, would
// evaluate [...] a lambda-expression.
// This is technically incorrect, there are some constant evaluated contexts
// where this should be allowed. We should probably fix this when DR1607 is
// ratified, it lays out the exact set of conditions where we shouldn't
// allow a lambda-expression.
case ExpressionEvaluationContext::ConstantEvaluated:
// We don't actually diagnose this case immediately, because we
// could be within a context where we might find out later that
// the expression is potentially evaluated (e.g., for typeid).
case ExpressionEvaluationContext::DiscardedStatement:
case ExpressionEvaluationContext::PotentiallyEvaluated:
case ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed:
return MaybeBindToTemporary(Lambda);
ExprResult Sema::BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
SourceLocation ConvLocation,
CXXConversionDecl *Conv,
Expr *Src) {
// Make sure that the lambda call operator is marked used.
CXXRecordDecl *Lambda = Conv->getParent();
CXXMethodDecl *CallOperator
= cast<CXXMethodDecl>(
ExprResult Init = PerformCopyInitialization(
InitializedEntity::InitializeLambdaToBlock(ConvLocation, Src->getType(),
CurrentLocation, Src);
if (!Init.isInvalid())
Init = ActOnFinishFullExpr(Init.get(), /*DiscardedValue*/ false);
if (Init.isInvalid())
return ExprError();
// Create the new block to be returned.
BlockDecl *Block = BlockDecl::Create(Context, CurContext, ConvLocation);
// Set the type information.
// Add parameters.
SmallVector<ParmVarDecl *, 4> BlockParams;
for (unsigned I = 0, N = CallOperator->getNumParams(); I != N; ++I) {
ParmVarDecl *From = CallOperator->getParamDecl(I);
Context, Block, From->getBeginLoc(), From->getLocation(),
From->getIdentifier(), From->getType(), From->getTypeSourceInfo(),
// Add capture. The capture uses a fake variable, which doesn't correspond
// to any actual memory location. However, the initializer copy-initializes
// the lambda object.
TypeSourceInfo *CapVarTSI =
VarDecl *CapVar = VarDecl::Create(Context, Block, ConvLocation,
ConvLocation, nullptr,
Src->getType(), CapVarTSI,
BlockDecl::Capture Capture(/*variable=*/CapVar, /*byRef=*/false,
/*nested=*/false, /*copy=*/Init.get());
Block->setCaptures(Context, Capture, /*CapturesCXXThis=*/false);
// Add a fake function body to the block. IR generation is responsible
// for filling in the actual body, which cannot be expressed as an AST.
Block->setBody(new (Context) CompoundStmt(ConvLocation));
// Create the block literal expression.
Expr *BuildBlock = new (Context) BlockExpr(Block, Conv->getConversionType());
return BuildBlock;