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//===--- SemaExceptionSpec.cpp - C++ Exception Specifications ---*- C++ -*-===//
// 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 provides Sema routines for C++ exception specification testing.
#include "clang/Sema/SemaInternal.h"
#include "clang/AST/ASTMutationListener.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/TypeLoc.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/SourceManager.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallString.h"
namespace clang {
static const FunctionProtoType *GetUnderlyingFunction(QualType T)
if (const PointerType *PtrTy = T->getAs<PointerType>())
T = PtrTy->getPointeeType();
else if (const ReferenceType *RefTy = T->getAs<ReferenceType>())
T = RefTy->getPointeeType();
else if (const MemberPointerType *MPTy = T->getAs<MemberPointerType>())
T = MPTy->getPointeeType();
return T->getAs<FunctionProtoType>();
/// HACK: libstdc++ has a bug where it shadows std::swap with a member
/// swap function then tries to call std::swap unqualified from the exception
/// specification of that function. This function detects whether we're in
/// such a case and turns off delay-parsing of exception specifications.
bool Sema::isLibstdcxxEagerExceptionSpecHack(const Declarator &D) {
auto *RD = dyn_cast<CXXRecordDecl>(CurContext);
// All the problem cases are member functions named "swap" within class
// templates declared directly within namespace std or std::__debug or
// std::__profile.
if (!RD || !RD->getIdentifier() || !RD->getDescribedClassTemplate() ||
!D.getIdentifier() || !D.getIdentifier()->isStr("swap"))
return false;
auto *ND = dyn_cast<NamespaceDecl>(RD->getDeclContext());
if (!ND)
return false;
bool IsInStd = ND->isStdNamespace();
if (!IsInStd) {
// This isn't a direct member of namespace std, but it might still be
// libstdc++'s std::__debug::array or std::__profile::array.
IdentifierInfo *II = ND->getIdentifier();
if (!II || !(II->isStr("__debug") || II->isStr("__profile")) ||
return false;
// Only apply this hack within a system header.
if (!Context.getSourceManager().isInSystemHeader(D.getBeginLoc()))
return false;
return llvm::StringSwitch<bool>(RD->getIdentifier()->getName())
.Case("array", true)
.Case("pair", IsInStd)
.Case("priority_queue", IsInStd)
.Case("stack", IsInStd)
.Case("queue", IsInStd)
ExprResult Sema::ActOnNoexceptSpec(SourceLocation NoexceptLoc,
Expr *NoexceptExpr,
ExceptionSpecificationType &EST) {
// FIXME: This is bogus, a noexcept expression is not a condition.
ExprResult Converted = CheckBooleanCondition(NoexceptLoc, NoexceptExpr);
if (Converted.isInvalid())
return Converted;
if (Converted.get()->isValueDependent()) {
EST = EST_DependentNoexcept;
return Converted;
llvm::APSInt Result;
Converted = VerifyIntegerConstantExpression(
Converted.get(), &Result,
/*AllowFold*/ false);
if (!Converted.isInvalid())
EST = !Result ? EST_NoexceptFalse : EST_NoexceptTrue;
return Converted;
/// CheckSpecifiedExceptionType - Check if the given type is valid in an
/// exception specification. Incomplete types, or pointers to incomplete types
/// other than void are not allowed.
/// \param[in,out] T The exception type. This will be decayed to a pointer type
/// when the input is an array or a function type.
bool Sema::CheckSpecifiedExceptionType(QualType &T, SourceRange Range) {
// C++11 [except.spec]p2:
// A type cv T, "array of T", or "function returning T" denoted
// in an exception-specification is adjusted to type T, "pointer to T", or
// "pointer to function returning T", respectively.
// We also apply this rule in C++98.
if (T->isArrayType())
T = Context.getArrayDecayedType(T);
else if (T->isFunctionType())
T = Context.getPointerType(T);
int Kind = 0;
QualType PointeeT = T;
if (const PointerType *PT = T->getAs<PointerType>()) {
PointeeT = PT->getPointeeType();
Kind = 1;
// cv void* is explicitly permitted, despite being a pointer to an
// incomplete type.
if (PointeeT->isVoidType())
return false;
} else if (const ReferenceType *RT = T->getAs<ReferenceType>()) {
PointeeT = RT->getPointeeType();
Kind = 2;
if (RT->isRValueReferenceType()) {
// C++11 [except.spec]p2:
// A type denoted in an exception-specification shall not denote [...]
// an rvalue reference type.
Diag(Range.getBegin(), diag::err_rref_in_exception_spec)
<< T << Range;
return true;
// C++11 [except.spec]p2:
// A type denoted in an exception-specification shall not denote an
// incomplete type other than a class currently being defined [...].
// A type denoted in an exception-specification shall not denote a
// pointer or reference to an incomplete type, other than (cv) void* or a
// pointer or reference to a class currently being defined.
// In Microsoft mode, downgrade this to a warning.
unsigned DiagID = diag::err_incomplete_in_exception_spec;
bool ReturnValueOnError = true;
if (getLangOpts().MSVCCompat) {
DiagID = diag::ext_incomplete_in_exception_spec;
ReturnValueOnError = false;
if (!(PointeeT->isRecordType() &&
PointeeT->castAs<RecordType>()->isBeingDefined()) &&
RequireCompleteType(Range.getBegin(), PointeeT, DiagID, Kind, Range))
return ReturnValueOnError;
return false;
/// CheckDistantExceptionSpec - Check if the given type is a pointer or pointer
/// to member to a function with an exception specification. This means that
/// it is invalid to add another level of indirection.
bool Sema::CheckDistantExceptionSpec(QualType T) {
// C++17 removes this rule in favor of putting exception specifications into
// the type system.
if (getLangOpts().CPlusPlus17)
return false;
if (const PointerType *PT = T->getAs<PointerType>())
T = PT->getPointeeType();
else if (const MemberPointerType *PT = T->getAs<MemberPointerType>())
T = PT->getPointeeType();
return false;
const FunctionProtoType *FnT = T->getAs<FunctionProtoType>();
if (!FnT)
return false;
return FnT->hasExceptionSpec();
const FunctionProtoType *
Sema::ResolveExceptionSpec(SourceLocation Loc, const FunctionProtoType *FPT) {
if (FPT->getExceptionSpecType() == EST_Unparsed) {
Diag(Loc, diag::err_exception_spec_not_parsed);
return nullptr;
if (!isUnresolvedExceptionSpec(FPT->getExceptionSpecType()))
return FPT;
FunctionDecl *SourceDecl = FPT->getExceptionSpecDecl();
const FunctionProtoType *SourceFPT =
// If the exception specification has already been resolved, just return it.
if (!isUnresolvedExceptionSpec(SourceFPT->getExceptionSpecType()))
return SourceFPT;
// Compute or instantiate the exception specification now.
if (SourceFPT->getExceptionSpecType() == EST_Unevaluated)
EvaluateImplicitExceptionSpec(Loc, cast<CXXMethodDecl>(SourceDecl));
InstantiateExceptionSpec(Loc, SourceDecl);
const FunctionProtoType *Proto =
if (Proto->getExceptionSpecType() == clang::EST_Unparsed) {
Diag(Loc, diag::err_exception_spec_not_parsed);
Proto = nullptr;
return Proto;
Sema::UpdateExceptionSpec(FunctionDecl *FD,
const FunctionProtoType::ExceptionSpecInfo &ESI) {
// If we've fully resolved the exception specification, notify listeners.
if (!isUnresolvedExceptionSpec(ESI.Type))
if (auto *Listener = getASTMutationListener())
for (FunctionDecl *Redecl : FD->redecls())
Context.adjustExceptionSpec(Redecl, ESI);
static bool exceptionSpecNotKnownYet(const FunctionDecl *FD) {
auto *MD = dyn_cast<CXXMethodDecl>(FD);
if (!MD)
return false;
auto EST = MD->getType()->castAs<FunctionProtoType>()->getExceptionSpecType();
return EST == EST_Unparsed ||
(EST == EST_Unevaluated && MD->getParent()->isBeingDefined());
static bool CheckEquivalentExceptionSpecImpl(
Sema &S, const PartialDiagnostic &DiagID, const PartialDiagnostic &NoteID,
const FunctionProtoType *Old, SourceLocation OldLoc,
const FunctionProtoType *New, SourceLocation NewLoc,
bool *MissingExceptionSpecification = nullptr,
bool *MissingEmptyExceptionSpecification = nullptr,
bool AllowNoexceptAllMatchWithNoSpec = false, bool IsOperatorNew = false);
/// Determine whether a function has an implicitly-generated exception
/// specification.
static bool hasImplicitExceptionSpec(FunctionDecl *Decl) {
if (!isa<CXXDestructorDecl>(Decl) &&
Decl->getDeclName().getCXXOverloadedOperator() != OO_Delete &&
Decl->getDeclName().getCXXOverloadedOperator() != OO_Array_Delete)
return false;
// For a function that the user didn't declare:
// - if this is a destructor, its exception specification is implicit.
// - if this is 'operator delete' or 'operator delete[]', the exception
// specification is as-if an explicit exception specification was given
// (per []p2).
if (!Decl->getTypeSourceInfo())
return isa<CXXDestructorDecl>(Decl);
const FunctionProtoType *Ty =
return !Ty->hasExceptionSpec();
bool Sema::CheckEquivalentExceptionSpec(FunctionDecl *Old, FunctionDecl *New) {
// Just completely ignore this under -fno-exceptions prior to C++17.
// In C++17 onwards, the exception specification is part of the type and
// we will diagnose mismatches anyway, so it's better to check for them here.
if (!getLangOpts().CXXExceptions && !getLangOpts().CPlusPlus17)
return false;
OverloadedOperatorKind OO = New->getDeclName().getCXXOverloadedOperator();
bool IsOperatorNew = OO == OO_New || OO == OO_Array_New;
bool MissingExceptionSpecification = false;
bool MissingEmptyExceptionSpecification = false;
unsigned DiagID = diag::err_mismatched_exception_spec;
bool ReturnValueOnError = true;
if (getLangOpts().MSVCCompat) {
DiagID = diag::ext_mismatched_exception_spec;
ReturnValueOnError = false;
// If we're befriending a member function of a class that's currently being
// defined, we might not be able to work out its exception specification yet.
// If not, defer the check until later.
if (exceptionSpecNotKnownYet(Old) || exceptionSpecNotKnownYet(New)) {
DelayedEquivalentExceptionSpecChecks.push_back({New, Old});
return false;
// Check the types as written: they must match before any exception
// specification adjustment is applied.
if (!CheckEquivalentExceptionSpecImpl(
*this, PDiag(DiagID), PDiag(diag::note_previous_declaration),
Old->getType()->getAs<FunctionProtoType>(), Old->getLocation(),
New->getType()->getAs<FunctionProtoType>(), New->getLocation(),
&MissingExceptionSpecification, &MissingEmptyExceptionSpecification,
/*AllowNoexceptAllMatchWithNoSpec=*/true, IsOperatorNew)) {
// C++11 [except.spec]p4 [DR1492]:
// If a declaration of a function has an implicit
// exception-specification, other declarations of the function shall
// not specify an exception-specification.
if (getLangOpts().CPlusPlus11 && getLangOpts().CXXExceptions &&
hasImplicitExceptionSpec(Old) != hasImplicitExceptionSpec(New)) {
Diag(New->getLocation(), diag::ext_implicit_exception_spec_mismatch)
<< hasImplicitExceptionSpec(Old);
if (Old->getLocation().isValid())
Diag(Old->getLocation(), diag::note_previous_declaration);
return false;
// The failure was something other than an missing exception
// specification; return an error, except in MS mode where this is a warning.
if (!MissingExceptionSpecification)
return ReturnValueOnError;
const FunctionProtoType *NewProto =
// The new function declaration is only missing an empty exception
// specification "throw()". If the throw() specification came from a
// function in a system header that has C linkage, just add an empty
// exception specification to the "new" declaration. Note that C library
// implementations are permitted to add these nothrow exception
// specifications.
// Likewise if the old function is a builtin.
if (MissingEmptyExceptionSpecification && NewProto &&
(Old->getLocation().isInvalid() ||
Context.getSourceManager().isInSystemHeader(Old->getLocation()) ||
Old->getBuiltinID()) &&
Old->isExternC()) {
NewProto->getReturnType(), NewProto->getParamTypes(),
return false;
const FunctionProtoType *OldProto =
FunctionProtoType::ExceptionSpecInfo ESI = OldProto->getExceptionSpecType();
if (ESI.Type == EST_Dynamic) {
// FIXME: What if the exceptions are described in terms of the old
// prototype's parameters?
ESI.Exceptions = OldProto->exceptions();
if (ESI.Type == EST_NoexceptFalse)
ESI.Type = EST_None;
if (ESI.Type == EST_NoexceptTrue)
ESI.Type = EST_BasicNoexcept;
// For dependent noexcept, we can't just take the expression from the old
// prototype. It likely contains references to the old prototype's parameters.
if (ESI.Type == EST_DependentNoexcept) {
} else {
// Update the type of the function with the appropriate exception
// specification.
NewProto->getReturnType(), NewProto->getParamTypes(),
if (getLangOpts().MSVCCompat && ESI.Type != EST_DependentNoexcept) {
// Allow missing exception specifications in redeclarations as an extension.
DiagID = diag::ext_ms_missing_exception_specification;
ReturnValueOnError = false;
} else if (New->isReplaceableGlobalAllocationFunction() &&
ESI.Type != EST_DependentNoexcept) {
// Allow missing exception specifications in redeclarations as an extension,
// when declaring a replaceable global allocation function.
DiagID = diag::ext_missing_exception_specification;
ReturnValueOnError = false;
} else if (ESI.Type == EST_NoThrow) {
// Allow missing attribute 'nothrow' in redeclarations, since this is a very
// common omission.
DiagID = diag::ext_missing_exception_specification;
ReturnValueOnError = false;
} else {
DiagID = diag::err_missing_exception_specification;
ReturnValueOnError = true;
// Warn about the lack of exception specification.
SmallString<128> ExceptionSpecString;
llvm::raw_svector_ostream OS(ExceptionSpecString);
switch (OldProto->getExceptionSpecType()) {
case EST_DynamicNone:
OS << "throw()";
case EST_Dynamic: {
OS << "throw(";
bool OnFirstException = true;
for (const auto &E : OldProto->exceptions()) {
if (OnFirstException)
OnFirstException = false;
OS << ", ";
OS << E.getAsString(getPrintingPolicy());
OS << ")";
case EST_BasicNoexcept:
OS << "noexcept";
case EST_DependentNoexcept:
case EST_NoexceptFalse:
case EST_NoexceptTrue:
OS << "noexcept(";
assert(OldProto->getNoexceptExpr() != nullptr && "Expected non-null Expr");
OldProto->getNoexceptExpr()->printPretty(OS, nullptr, getPrintingPolicy());
OS << ")";
case EST_NoThrow:
OS <<"__attribute__((nothrow))";
case EST_None:
case EST_MSAny:
case EST_Unevaluated:
case EST_Uninstantiated:
case EST_Unparsed:
llvm_unreachable("This spec type is compatible with none.");
SourceLocation FixItLoc;
if (TypeSourceInfo *TSInfo = New->getTypeSourceInfo()) {
TypeLoc TL = TSInfo->getTypeLoc().IgnoreParens();
// FIXME: Preserve enough information so that we can produce a correct fixit
// location when there is a trailing return type.
if (auto FTLoc = TL.getAs<FunctionProtoTypeLoc>())
if (!FTLoc.getTypePtr()->hasTrailingReturn())
FixItLoc = getLocForEndOfToken(FTLoc.getLocalRangeEnd());
if (FixItLoc.isInvalid())
Diag(New->getLocation(), DiagID)
<< New << OS.str();
else {
Diag(New->getLocation(), DiagID)
<< New << OS.str()
<< FixItHint::CreateInsertion(FixItLoc, " " + OS.str().str());
if (Old->getLocation().isValid())
Diag(Old->getLocation(), diag::note_previous_declaration);
return ReturnValueOnError;
/// CheckEquivalentExceptionSpec - Check if the two types have equivalent
/// exception specifications. Exception specifications are equivalent if
/// they allow exactly the same set of exception types. It does not matter how
/// that is achieved. See C++ [except.spec]p2.
bool Sema::CheckEquivalentExceptionSpec(
const FunctionProtoType *Old, SourceLocation OldLoc,
const FunctionProtoType *New, SourceLocation NewLoc) {
if (!getLangOpts().CXXExceptions)
return false;
unsigned DiagID = diag::err_mismatched_exception_spec;
if (getLangOpts().MSVCCompat)
DiagID = diag::ext_mismatched_exception_spec;
bool Result = CheckEquivalentExceptionSpecImpl(
*this, PDiag(DiagID), PDiag(diag::note_previous_declaration),
Old, OldLoc, New, NewLoc);
// In Microsoft mode, mismatching exception specifications just cause a warning.
if (getLangOpts().MSVCCompat)
return false;
return Result;
/// CheckEquivalentExceptionSpec - Check if the two types have compatible
/// exception specifications. See C++ [except.spec]p3.
/// \return \c false if the exception specifications match, \c true if there is
/// a problem. If \c true is returned, either a diagnostic has already been
/// produced or \c *MissingExceptionSpecification is set to \c true.
static bool CheckEquivalentExceptionSpecImpl(
Sema &S, const PartialDiagnostic &DiagID, const PartialDiagnostic &NoteID,
const FunctionProtoType *Old, SourceLocation OldLoc,
const FunctionProtoType *New, SourceLocation NewLoc,
bool *MissingExceptionSpecification,
bool *MissingEmptyExceptionSpecification,
bool AllowNoexceptAllMatchWithNoSpec, bool IsOperatorNew) {
if (MissingExceptionSpecification)
*MissingExceptionSpecification = false;
if (MissingEmptyExceptionSpecification)
*MissingEmptyExceptionSpecification = false;
Old = S.ResolveExceptionSpec(NewLoc, Old);
if (!Old)
return false;
New = S.ResolveExceptionSpec(NewLoc, New);
if (!New)
return false;
// C++0x [except.spec]p3: Two exception-specifications are compatible if:
// - both are non-throwing, regardless of their form,
// - both have the form noexcept(constant-expression) and the constant-
// expressions are equivalent,
// - both are dynamic-exception-specifications that have the same set of
// adjusted types.
// C++0x [except.spec]p12: An exception-specification is non-throwing if it is
// of the form throw(), noexcept, or noexcept(constant-expression) where the
// constant-expression yields true.
// C++0x [except.spec]p4: If any declaration of a function has an exception-
// specifier that is not a noexcept-specification allowing all exceptions,
// all declarations [...] of that function shall have a compatible
// exception-specification.
// That last point basically means that noexcept(false) matches no spec.
// It's considered when AllowNoexceptAllMatchWithNoSpec is true.
ExceptionSpecificationType OldEST = Old->getExceptionSpecType();
ExceptionSpecificationType NewEST = New->getExceptionSpecType();
assert(!isUnresolvedExceptionSpec(OldEST) &&
!isUnresolvedExceptionSpec(NewEST) &&
"Shouldn't see unknown exception specifications here");
CanThrowResult OldCanThrow = Old->canThrow();
CanThrowResult NewCanThrow = New->canThrow();
// Any non-throwing specifications are compatible.
if (OldCanThrow == CT_Cannot && NewCanThrow == CT_Cannot)
return false;
// Any throws-anything specifications are usually compatible.
if (OldCanThrow == CT_Can && OldEST != EST_Dynamic &&
NewCanThrow == CT_Can && NewEST != EST_Dynamic) {
// The exception is that the absence of an exception specification only
// matches noexcept(false) for functions, as described above.
if (!AllowNoexceptAllMatchWithNoSpec &&
((OldEST == EST_None && NewEST == EST_NoexceptFalse) ||
(OldEST == EST_NoexceptFalse && NewEST == EST_None))) {
// This is the disallowed case.
} else {
return false;
// C++14 [except.spec]p3:
// Two exception-specifications are compatible if [...] both have the form
// noexcept(constant-expression) and the constant-expressions are equivalent
if (OldEST == EST_DependentNoexcept && NewEST == EST_DependentNoexcept) {
llvm::FoldingSetNodeID OldFSN, NewFSN;
Old->getNoexceptExpr()->Profile(OldFSN, S.Context, true);
New->getNoexceptExpr()->Profile(NewFSN, S.Context, true);
if (OldFSN == NewFSN)
return false;
// Dynamic exception specifications with the same set of adjusted types
// are compatible.
if (OldEST == EST_Dynamic && NewEST == EST_Dynamic) {
bool Success = true;
// Both have a dynamic exception spec. Collect the first set, then compare
// to the second.
llvm::SmallPtrSet<CanQualType, 8> OldTypes, NewTypes;
for (const auto &I : Old->exceptions())
for (const auto &I : New->exceptions()) {
CanQualType TypePtr = S.Context.getCanonicalType(I).getUnqualifiedType();
if (OldTypes.count(TypePtr))
else {
Success = false;
if (Success && OldTypes.size() == NewTypes.size())
return false;
// As a special compatibility feature, under C++0x we accept no spec and
// throw(std::bad_alloc) as equivalent for operator new and operator new[].
// This is because the implicit declaration changed, but old code would break.
if (S.getLangOpts().CPlusPlus11 && IsOperatorNew) {
const FunctionProtoType *WithExceptions = nullptr;
if (OldEST == EST_None && NewEST == EST_Dynamic)
WithExceptions = New;
else if (OldEST == EST_Dynamic && NewEST == EST_None)
WithExceptions = Old;
if (WithExceptions && WithExceptions->getNumExceptions() == 1) {
// One has no spec, the other throw(something). If that something is
// std::bad_alloc, all conditions are met.
QualType Exception = *WithExceptions->exception_begin();
if (CXXRecordDecl *ExRecord = Exception->getAsCXXRecordDecl()) {
IdentifierInfo* Name = ExRecord->getIdentifier();
if (Name && Name->getName() == "bad_alloc") {
// It's called bad_alloc, but is it in std?
if (ExRecord->isInStdNamespace()) {
return false;
// If the caller wants to handle the case that the new function is
// incompatible due to a missing exception specification, let it.
if (MissingExceptionSpecification && OldEST != EST_None &&
NewEST == EST_None) {
// The old type has an exception specification of some sort, but
// the new type does not.
*MissingExceptionSpecification = true;
if (MissingEmptyExceptionSpecification && OldCanThrow == CT_Cannot) {
// The old type has a throw() or noexcept(true) exception specification
// and the new type has no exception specification, and the caller asked
// to handle this itself.
*MissingEmptyExceptionSpecification = true;
return true;
S.Diag(NewLoc, DiagID);
if (NoteID.getDiagID() != 0 && OldLoc.isValid())
S.Diag(OldLoc, NoteID);
return true;
bool Sema::CheckEquivalentExceptionSpec(const PartialDiagnostic &DiagID,
const PartialDiagnostic &NoteID,
const FunctionProtoType *Old,
SourceLocation OldLoc,
const FunctionProtoType *New,
SourceLocation NewLoc) {
if (!getLangOpts().CXXExceptions)
return false;
return CheckEquivalentExceptionSpecImpl(*this, DiagID, NoteID, Old, OldLoc,
New, NewLoc);
bool Sema::handlerCanCatch(QualType HandlerType, QualType ExceptionType) {
// [except.handle]p3:
// A handler is a match for an exception object of type E if:
// HandlerType must be ExceptionType or derived from it, or pointer or
// reference to such types.
const ReferenceType *RefTy = HandlerType->getAs<ReferenceType>();
if (RefTy)
HandlerType = RefTy->getPointeeType();
// -- the handler is of type cv T or cv T& and E and T are the same type
if (Context.hasSameUnqualifiedType(ExceptionType, HandlerType))
return true;
// FIXME: ObjC pointer types?
if (HandlerType->isPointerType() || HandlerType->isMemberPointerType()) {
if (RefTy && (!HandlerType.isConstQualified() ||
return false;
// -- the handler is of type cv T or const T& where T is a pointer or
// pointer to member type and E is std::nullptr_t
if (ExceptionType->isNullPtrType())
return true;
// -- the handler is of type cv T or const T& where T is a pointer or
// pointer to member type and E is a pointer or pointer to member type
// that can be converted to T by one or more of
// -- a qualification conversion
// -- a function pointer conversion
bool LifetimeConv;
QualType Result;
// FIXME: Should we treat the exception as catchable if a lifetime
// conversion is required?
if (IsQualificationConversion(ExceptionType, HandlerType, false,
LifetimeConv) ||
IsFunctionConversion(ExceptionType, HandlerType, Result))
return true;
// -- a standard pointer conversion [...]
if (!ExceptionType->isPointerType() || !HandlerType->isPointerType())
return false;
// Handle the "qualification conversion" portion.
Qualifiers EQuals, HQuals;
ExceptionType = Context.getUnqualifiedArrayType(
ExceptionType->getPointeeType(), EQuals);
HandlerType = Context.getUnqualifiedArrayType(
HandlerType->getPointeeType(), HQuals);
if (!HQuals.compatiblyIncludes(EQuals))
return false;
if (HandlerType->isVoidType() && ExceptionType->isObjectType())
return true;
// The only remaining case is a derived-to-base conversion.
// -- the handler is of type cg T or cv T& and T is an unambiguous public
// base class of E
if (!ExceptionType->isRecordType() || !HandlerType->isRecordType())
return false;
CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
if (!IsDerivedFrom(SourceLocation(), ExceptionType, HandlerType, Paths) ||
return false;
// Do this check from a context without privileges.
switch (CheckBaseClassAccess(SourceLocation(), HandlerType, ExceptionType,
/*Diagnostic*/ 0,
/*ForceCheck*/ true,
/*ForceUnprivileged*/ true)) {
case AR_accessible: return true;
case AR_inaccessible: return false;
case AR_dependent:
llvm_unreachable("access check dependent for unprivileged context");
case AR_delayed:
llvm_unreachable("access check delayed in non-declaration");
llvm_unreachable("unexpected access check result");
/// CheckExceptionSpecSubset - Check whether the second function type's
/// exception specification is a subset (or equivalent) of the first function
/// type. This is used by override and pointer assignment checks.
bool Sema::CheckExceptionSpecSubset(const PartialDiagnostic &DiagID,
const PartialDiagnostic &NestedDiagID,
const PartialDiagnostic &NoteID,
const PartialDiagnostic &NoThrowDiagID,
const FunctionProtoType *Superset,
SourceLocation SuperLoc,
const FunctionProtoType *Subset,
SourceLocation SubLoc) {
// Just auto-succeed under -fno-exceptions.
if (!getLangOpts().CXXExceptions)
return false;
// FIXME: As usual, we could be more specific in our error messages, but
// that better waits until we've got types with source locations.
if (!SubLoc.isValid())
SubLoc = SuperLoc;
// Resolve the exception specifications, if needed.
Superset = ResolveExceptionSpec(SuperLoc, Superset);
if (!Superset)
return false;
Subset = ResolveExceptionSpec(SubLoc, Subset);
if (!Subset)
return false;
ExceptionSpecificationType SuperEST = Superset->getExceptionSpecType();
ExceptionSpecificationType SubEST = Subset->getExceptionSpecType();
assert(!isUnresolvedExceptionSpec(SuperEST) &&
!isUnresolvedExceptionSpec(SubEST) &&
"Shouldn't see unknown exception specifications here");
// If there are dependent noexcept specs, assume everything is fine. Unlike
// with the equivalency check, this is safe in this case, because we don't
// want to merge declarations. Checks after instantiation will catch any
// omissions we make here.
if (SuperEST == EST_DependentNoexcept || SubEST == EST_DependentNoexcept)
return false;
CanThrowResult SuperCanThrow = Superset->canThrow();
CanThrowResult SubCanThrow = Subset->canThrow();
// If the superset contains everything or the subset contains nothing, we're
// done.
if ((SuperCanThrow == CT_Can && SuperEST != EST_Dynamic) ||
SubCanThrow == CT_Cannot)
return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
Subset, SubLoc);
// Allow __declspec(nothrow) to be missing on redeclaration as an extension in
// some cases.
if (NoThrowDiagID.getDiagID() != 0 && SubCanThrow == CT_Can &&
SuperCanThrow == CT_Cannot && SuperEST == EST_NoThrow) {
Diag(SubLoc, NoThrowDiagID);
if (NoteID.getDiagID() != 0)
Diag(SuperLoc, NoteID);
return true;
// If the subset contains everything or the superset contains nothing, we've
// failed.
if ((SubCanThrow == CT_Can && SubEST != EST_Dynamic) ||
SuperCanThrow == CT_Cannot) {
Diag(SubLoc, DiagID);
if (NoteID.getDiagID() != 0)
Diag(SuperLoc, NoteID);
return true;
assert(SuperEST == EST_Dynamic && SubEST == EST_Dynamic &&
"Exception spec subset: non-dynamic case slipped through.");
// Neither contains everything or nothing. Do a proper comparison.
for (QualType SubI : Subset->exceptions()) {
if (const ReferenceType *RefTy = SubI->getAs<ReferenceType>())
SubI = RefTy->getPointeeType();
// Make sure it's in the superset.
bool Contained = false;
for (QualType SuperI : Superset->exceptions()) {
// [except.spec]p5:
// the target entity shall allow at least the exceptions allowed by the
// source
// We interpret this as meaning that a handler for some target type would
// catch an exception of each source type.
if (handlerCanCatch(SuperI, SubI)) {
Contained = true;
if (!Contained) {
Diag(SubLoc, DiagID);
if (NoteID.getDiagID() != 0)
Diag(SuperLoc, NoteID);
return true;
// We've run half the gauntlet.
return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
Subset, SubLoc);
static bool
CheckSpecForTypesEquivalent(Sema &S, const PartialDiagnostic &DiagID,
const PartialDiagnostic &NoteID, QualType Target,
SourceLocation TargetLoc, QualType Source,
SourceLocation SourceLoc) {
const FunctionProtoType *TFunc = GetUnderlyingFunction(Target);
if (!TFunc)
return false;
const FunctionProtoType *SFunc = GetUnderlyingFunction(Source);
if (!SFunc)
return false;
return S.CheckEquivalentExceptionSpec(DiagID, NoteID, TFunc, TargetLoc,
SFunc, SourceLoc);
/// CheckParamExceptionSpec - Check if the parameter and return types of the
/// two functions have equivalent exception specs. This is part of the
/// assignment and override compatibility check. We do not check the parameters
/// of parameter function pointers recursively, as no sane programmer would
/// even be able to write such a function type.
bool Sema::CheckParamExceptionSpec(const PartialDiagnostic &DiagID,
const PartialDiagnostic &NoteID,
const FunctionProtoType *Target,
SourceLocation TargetLoc,
const FunctionProtoType *Source,
SourceLocation SourceLoc) {
auto RetDiag = DiagID;
RetDiag << 0;
if (CheckSpecForTypesEquivalent(
*this, RetDiag, PDiag(),
Target->getReturnType(), TargetLoc, Source->getReturnType(),
return true;
// We shouldn't even be testing this unless the arguments are otherwise
// compatible.
assert(Target->getNumParams() == Source->getNumParams() &&
"Functions have different argument counts.");
for (unsigned i = 0, E = Target->getNumParams(); i != E; ++i) {
auto ParamDiag = DiagID;
ParamDiag << 1;
if (CheckSpecForTypesEquivalent(
*this, ParamDiag, PDiag(),
Target->getParamType(i), TargetLoc, Source->getParamType(i),
return true;
return false;
bool Sema::CheckExceptionSpecCompatibility(Expr *From, QualType ToType) {
// First we check for applicability.
// Target type must be a function, function pointer or function reference.
const FunctionProtoType *ToFunc = GetUnderlyingFunction(ToType);
if (!ToFunc || ToFunc->hasDependentExceptionSpec())
return false;
// SourceType must be a function or function pointer.
const FunctionProtoType *FromFunc = GetUnderlyingFunction(From->getType());
if (!FromFunc || FromFunc->hasDependentExceptionSpec())
return false;
unsigned DiagID = diag::err_incompatible_exception_specs;
unsigned NestedDiagID = diag::err_deep_exception_specs_differ;
// This is not an error in C++17 onwards, unless the noexceptness doesn't
// match, but in that case we have a full-on type mismatch, not just a
// type sugar mismatch.
if (getLangOpts().CPlusPlus17) {
DiagID = diag::warn_incompatible_exception_specs;
NestedDiagID = diag::warn_deep_exception_specs_differ;
// Now we've got the correct types on both sides, check their compatibility.
// This means that the source of the conversion can only throw a subset of
// the exceptions of the target, and any exception specs on arguments or
// return types must be equivalent.
// FIXME: If there is a nested dependent exception specification, we should
// not be checking it here. This is fine:
// template<typename T> void f() {
// void (*p)(void (*) throw(T));
// void (*q)(void (*) throw(int)) = p;
// }
// ... because it might be instantiated with T=int.
return CheckExceptionSpecSubset(
PDiag(DiagID), PDiag(NestedDiagID), PDiag(), PDiag(), ToFunc,
From->getSourceRange().getBegin(), FromFunc, SourceLocation()) &&
bool Sema::CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
const CXXMethodDecl *Old) {
// If the new exception specification hasn't been parsed yet, skip the check.
// We'll get called again once it's been parsed.
if (New->getType()->castAs<FunctionProtoType>()->getExceptionSpecType() ==
return false;
// Don't check uninstantiated template destructors at all. We can only
// synthesize correct specs after the template is instantiated.
if (isa<CXXDestructorDecl>(New) && New->getParent()->isDependentType())
return false;
// If the old exception specification hasn't been parsed yet, or the new
// exception specification can't be computed yet, remember that we need to
// perform this check when we get to the end of the outermost
// lexically-surrounding class.
if (exceptionSpecNotKnownYet(Old) || exceptionSpecNotKnownYet(New)) {
DelayedOverridingExceptionSpecChecks.push_back({New, Old});
return false;
unsigned DiagID = diag::err_override_exception_spec;
if (getLangOpts().MSVCCompat)
DiagID = diag::ext_override_exception_spec;
return CheckExceptionSpecSubset(PDiag(DiagID),
static CanThrowResult canSubExprsThrow(Sema &S, const Expr *E) {
CanThrowResult R = CT_Cannot;
for (const Stmt *SubStmt : E->children()) {
R = mergeCanThrow(R, S.canThrow(cast<Expr>(SubStmt)));
if (R == CT_Can)
return R;
static CanThrowResult canCalleeThrow(Sema &S, const Expr *E, const Decl *D) {
// As an extension, we assume that __attribute__((nothrow)) functions don't
// throw.
if (D && isa<FunctionDecl>(D) && D->hasAttr<NoThrowAttr>())
return CT_Cannot;
QualType T;
// In C++1z, just look at the function type of the callee.
if (S.getLangOpts().CPlusPlus17 && isa<CallExpr>(E)) {
E = cast<CallExpr>(E)->getCallee();
T = E->getType();
if (T->isSpecificPlaceholderType(BuiltinType::BoundMember)) {
// Sadly we don't preserve the actual type as part of the "bound member"
// placeholder, so we need to reconstruct it.
E = E->IgnoreParenImpCasts();
// Could be a call to a pointer-to-member or a plain member access.
if (auto *Op = dyn_cast<BinaryOperator>(E)) {
assert(Op->getOpcode() == BO_PtrMemD || Op->getOpcode() == BO_PtrMemI);
T = Op->getRHS()->getType()
} else {
T = cast<MemberExpr>(E)->getMemberDecl()->getType();
} else if (const ValueDecl *VD = dyn_cast_or_null<ValueDecl>(D))
T = VD->getType();
// If we have no clue what we're calling, assume the worst.
return CT_Can;
const FunctionProtoType *FT;
if ((FT = T->getAs<FunctionProtoType>())) {
} else if (const PointerType *PT = T->getAs<PointerType>())
FT = PT->getPointeeType()->getAs<FunctionProtoType>();
else if (const ReferenceType *RT = T->getAs<ReferenceType>())
FT = RT->getPointeeType()->getAs<FunctionProtoType>();
else if (const MemberPointerType *MT = T->getAs<MemberPointerType>())
FT = MT->getPointeeType()->getAs<FunctionProtoType>();
else if (const BlockPointerType *BT = T->getAs<BlockPointerType>())
FT = BT->getPointeeType()->getAs<FunctionProtoType>();
if (!FT)
return CT_Can;
FT = S.ResolveExceptionSpec(E->getBeginLoc(), FT);
if (!FT)
return CT_Can;
return FT->canThrow();
static CanThrowResult canDynamicCastThrow(const CXXDynamicCastExpr *DC) {
if (DC->isTypeDependent())
return CT_Dependent;
if (!DC->getTypeAsWritten()->isReferenceType())
return CT_Cannot;
if (DC->getSubExpr()->isTypeDependent())
return CT_Dependent;
return DC->getCastKind() == clang::CK_Dynamic? CT_Can : CT_Cannot;
static CanThrowResult canTypeidThrow(Sema &S, const CXXTypeidExpr *DC) {
if (DC->isTypeOperand())
return CT_Cannot;
Expr *Op = DC->getExprOperand();
if (Op->isTypeDependent())
return CT_Dependent;
const RecordType *RT = Op->getType()->getAs<RecordType>();
if (!RT)
return CT_Cannot;
if (!cast<CXXRecordDecl>(RT->getDecl())->isPolymorphic())
return CT_Cannot;
if (Op->Classify(S.Context).isPRValue())
return CT_Cannot;
return CT_Can;
CanThrowResult Sema::canThrow(const Expr *E) {
// C++ [expr.unary.noexcept]p3:
// [Can throw] if in a potentially-evaluated context the expression would
// contain:
switch (E->getStmtClass()) {
case Expr::ConstantExprClass:
return canThrow(cast<ConstantExpr>(E)->getSubExpr());
case Expr::CXXThrowExprClass:
// - a potentially evaluated throw-expression
return CT_Can;
case Expr::CXXDynamicCastExprClass: {
// - a potentially evaluated dynamic_cast expression dynamic_cast<T>(v),
// where T is a reference type, that requires a run-time check
CanThrowResult CT = canDynamicCastThrow(cast<CXXDynamicCastExpr>(E));
if (CT == CT_Can)
return CT;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
case Expr::CXXTypeidExprClass:
// - a potentially evaluated typeid expression applied to a glvalue
// expression whose type is a polymorphic class type
return canTypeidThrow(*this, cast<CXXTypeidExpr>(E));
// - a potentially evaluated call to a function, member function, function
// pointer, or member function pointer that does not have a non-throwing
// exception-specification
case Expr::CallExprClass:
case Expr::CXXMemberCallExprClass:
case Expr::CXXOperatorCallExprClass:
case Expr::UserDefinedLiteralClass: {
const CallExpr *CE = cast<CallExpr>(E);
CanThrowResult CT;
if (E->isTypeDependent())
CT = CT_Dependent;
else if (isa<CXXPseudoDestructorExpr>(CE->getCallee()->IgnoreParens()))
CT = CT_Cannot;
CT = canCalleeThrow(*this, E, CE->getCalleeDecl());
if (CT == CT_Can)
return CT;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
case Expr::CXXConstructExprClass:
case Expr::CXXTemporaryObjectExprClass: {
CanThrowResult CT = canCalleeThrow(*this, E,
if (CT == CT_Can)
return CT;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
case Expr::CXXInheritedCtorInitExprClass:
return canCalleeThrow(*this, E,
case Expr::LambdaExprClass: {
const LambdaExpr *Lambda = cast<LambdaExpr>(E);
CanThrowResult CT = CT_Cannot;
for (LambdaExpr::const_capture_init_iterator
Cap = Lambda->capture_init_begin(),
CapEnd = Lambda->capture_init_end();
Cap != CapEnd; ++Cap)
CT = mergeCanThrow(CT, canThrow(*Cap));
return CT;
case Expr::CXXNewExprClass: {
CanThrowResult CT;
if (E->isTypeDependent())
CT = CT_Dependent;
CT = canCalleeThrow(*this, E, cast<CXXNewExpr>(E)->getOperatorNew());
if (CT == CT_Can)
return CT;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
case Expr::CXXDeleteExprClass: {
CanThrowResult CT;
QualType DTy = cast<CXXDeleteExpr>(E)->getDestroyedType();
if (DTy.isNull() || DTy->isDependentType()) {
CT = CT_Dependent;
} else {
CT = canCalleeThrow(*this, E,
if (const RecordType *RT = DTy->getAs<RecordType>()) {
const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
const CXXDestructorDecl *DD = RD->getDestructor();
if (DD)
CT = mergeCanThrow(CT, canCalleeThrow(*this, E, DD));
if (CT == CT_Can)
return CT;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
case Expr::CXXBindTemporaryExprClass: {
// The bound temporary has to be destroyed again, which might throw.
CanThrowResult CT = canCalleeThrow(*this, E,
if (CT == CT_Can)
return CT;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
// ObjC message sends are like function calls, but never have exception
// specs.
case Expr::ObjCMessageExprClass:
case Expr::ObjCPropertyRefExprClass:
case Expr::ObjCSubscriptRefExprClass:
return CT_Can;
// All the ObjC literals that are implemented as calls are
// potentially throwing unless we decide to close off that
// possibility.
case Expr::ObjCArrayLiteralClass:
case Expr::ObjCDictionaryLiteralClass:
case Expr::ObjCBoxedExprClass:
return CT_Can;
// Many other things have subexpressions, so we have to test those.
// Some are simple:
case Expr::CoawaitExprClass:
case Expr::ConditionalOperatorClass:
case Expr::CompoundLiteralExprClass:
case Expr::CoyieldExprClass:
case Expr::CXXConstCastExprClass:
case Expr::CXXReinterpretCastExprClass:
case Expr::CXXRewrittenBinaryOperatorClass:
case Expr::BuiltinBitCastExprClass:
case Expr::CXXStdInitializerListExprClass:
case Expr::DesignatedInitExprClass:
case Expr::DesignatedInitUpdateExprClass:
case Expr::ExprWithCleanupsClass:
case Expr::ExtVectorElementExprClass:
case Expr::InitListExprClass:
case Expr::ArrayInitLoopExprClass:
case Expr::MemberExprClass:
case Expr::ObjCIsaExprClass:
case Expr::ObjCIvarRefExprClass:
case Expr::ParenExprClass:
case Expr::ParenListExprClass:
case Expr::ShuffleVectorExprClass:
case Expr::ConvertVectorExprClass:
case Expr::VAArgExprClass:
return canSubExprsThrow(*this, E);
// Some might be dependent for other reasons.
case Expr::ArraySubscriptExprClass:
case Expr::OMPArraySectionExprClass:
case Expr::BinaryOperatorClass:
case Expr::DependentCoawaitExprClass:
case Expr::CompoundAssignOperatorClass:
case Expr::CStyleCastExprClass:
case Expr::CXXStaticCastExprClass:
case Expr::CXXFunctionalCastExprClass:
case Expr::ImplicitCastExprClass:
case Expr::MaterializeTemporaryExprClass:
case Expr::UnaryOperatorClass: {
CanThrowResult CT = E->isTypeDependent() ? CT_Dependent : CT_Cannot;
return mergeCanThrow(CT, canSubExprsThrow(*this, E));
// FIXME: We should handle StmtExpr, but that opens a MASSIVE can of worms.
case Expr::StmtExprClass:
return CT_Can;
case Expr::CXXDefaultArgExprClass:
return canThrow(cast<CXXDefaultArgExpr>(E)->getExpr());
case Expr::CXXDefaultInitExprClass:
return canThrow(cast<CXXDefaultInitExpr>(E)->getExpr());
case Expr::ChooseExprClass:
if (E->isTypeDependent() || E->isValueDependent())
return CT_Dependent;
return canThrow(cast<ChooseExpr>(E)->getChosenSubExpr());
case Expr::GenericSelectionExprClass:
if (cast<GenericSelectionExpr>(E)->isResultDependent())
return CT_Dependent;
return canThrow(cast<GenericSelectionExpr>(E)->getResultExpr());
// Some expressions are always dependent.
case Expr::CXXDependentScopeMemberExprClass:
case Expr::CXXUnresolvedConstructExprClass:
case Expr::DependentScopeDeclRefExprClass:
case Expr::CXXFoldExprClass:
return CT_Dependent;
case Expr::AsTypeExprClass:
case Expr::BinaryConditionalOperatorClass:
case Expr::BlockExprClass:
case Expr::CUDAKernelCallExprClass:
case Expr::DeclRefExprClass:
case Expr::ObjCBridgedCastExprClass:
case Expr::ObjCIndirectCopyRestoreExprClass:
case Expr::ObjCProtocolExprClass:
case Expr::ObjCSelectorExprClass:
case Expr::ObjCAvailabilityCheckExprClass:
case Expr::OffsetOfExprClass:
case Expr::PackExpansionExprClass:
case Expr::PseudoObjectExprClass:
case Expr::SubstNonTypeTemplateParmExprClass:
case Expr::SubstNonTypeTemplateParmPackExprClass:
case Expr::FunctionParmPackExprClass:
case Expr::UnaryExprOrTypeTraitExprClass:
case Expr::UnresolvedLookupExprClass:
case Expr::UnresolvedMemberExprClass:
case Expr::TypoExprClass:
// FIXME: Can any of the above throw? If so, when?
return CT_Cannot;
case Expr::AddrLabelExprClass:
case Expr::ArrayTypeTraitExprClass:
case Expr::AtomicExprClass:
case Expr::TypeTraitExprClass:
case Expr::CXXBoolLiteralExprClass:
case Expr::CXXNoexceptExprClass:
case Expr::CXXNullPtrLiteralExprClass:
case Expr::CXXPseudoDestructorExprClass:
case Expr::CXXScalarValueInitExprClass:
case Expr::CXXThisExprClass:
case Expr::CXXUuidofExprClass:
case Expr::CharacterLiteralClass:
case Expr::ExpressionTraitExprClass:
case Expr::FloatingLiteralClass:
case Expr::GNUNullExprClass:
case Expr::ImaginaryLiteralClass:
case Expr::ImplicitValueInitExprClass:
case Expr::IntegerLiteralClass:
case Expr::FixedPointLiteralClass:
case Expr::ArrayInitIndexExprClass:
case Expr::NoInitExprClass:
case Expr::ObjCEncodeExprClass:
case Expr::ObjCStringLiteralClass:
case Expr::ObjCBoolLiteralExprClass:
case Expr::OpaqueValueExprClass:
case Expr::PredefinedExprClass:
case Expr::SizeOfPackExprClass:
case Expr::StringLiteralClass:
case Expr::SourceLocExprClass:
case Expr::ConceptSpecializationExprClass:
// These expressions can never throw.
return CT_Cannot;
case Expr::MSPropertyRefExprClass:
case Expr::MSPropertySubscriptExprClass:
llvm_unreachable("Invalid class for expression");
#define STMT(CLASS, PARENT) case Expr::CLASS##Class:
#define STMT_RANGE(Base, First, Last)
#include "clang/AST/"
case Expr::NoStmtClass:
llvm_unreachable("Invalid class for expression");
llvm_unreachable("Bogus StmtClass");
} // end namespace clang