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//===--- SemaExceptionSpec.cpp - C++ Exception Specifications ---*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// 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.getLocStart()))
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)
/// 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().MicrosoftExt) {
DiagID = diag::ext_incomplete_in_exception_spec;
ReturnValueOnError = false;
if (!(PointeeT->isRecordType() &&
PointeeT->getAs<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().CPlusPlus1z)
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 (auto *Redecl : FD->redecls())
Context.adjustExceptionSpec(cast<FunctionDecl>(Redecl), ESI);
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++1z.
// In C++1z 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().CPlusPlus1z)
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().MicrosoftExt) {
DiagID = diag::ext_mismatched_exception_spec;
ReturnValueOnError = 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) {
ESI.Exceptions = OldProto->exceptions();
if (ESI.Type == EST_ComputedNoexcept) {
// For computed noexcept, we can't just take the expression from the old
// prototype. It likely contains references to the old prototype's
// parameters.
} else {
// Update the type of the function with the appropriate exception
// specification.
NewProto->getReturnType(), NewProto->getParamTypes(),
if (getLangOpts().MicrosoftExt && ESI.Type != EST_ComputedNoexcept) {
// 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_ComputedNoexcept) {
// 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 {
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_ComputedNoexcept:
OS << "noexcept(";
assert(OldProto->getNoexceptExpr() != nullptr && "Expected non-null Expr");
OldProto->getNoexceptExpr()->printPretty(OS, nullptr, getPrintingPolicy());
OS << ")";
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().MicrosoftExt)
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().MicrosoftExt)
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");
// Shortcut the case where both have no spec.
if (OldEST == EST_None && NewEST == EST_None)
return false;
FunctionProtoType::NoexceptResult OldNR = Old->getNoexceptSpec(S.Context);
FunctionProtoType::NoexceptResult NewNR = New->getNoexceptSpec(S.Context);
if (OldNR == FunctionProtoType::NR_BadNoexcept ||
NewNR == FunctionProtoType::NR_BadNoexcept)
return false;
// Dependent noexcept specifiers are compatible with each other, but nothing
// else.
// One noexcept is compatible with another if the argument is the same
if (OldNR == NewNR &&
OldNR != FunctionProtoType::NR_NoNoexcept &&
NewNR != FunctionProtoType::NR_NoNoexcept)
return false;
if (OldNR != NewNR &&
OldNR != FunctionProtoType::NR_NoNoexcept &&
NewNR != FunctionProtoType::NR_NoNoexcept) {
S.Diag(NewLoc, DiagID);
if (NoteID.getDiagID() != 0 && OldLoc.isValid())
S.Diag(OldLoc, NoteID);
return true;
// The MS extension throw(...) is compatible with itself.
if (OldEST == EST_MSAny && NewEST == EST_MSAny)
return false;
// It's also compatible with no spec.
if ((OldEST == EST_None && NewEST == EST_MSAny) ||
(OldEST == EST_MSAny && NewEST == EST_None))
return false;
// It's also compatible with noexcept(false).
if (OldEST == EST_MSAny && NewNR == FunctionProtoType::NR_Throw)
return false;
if (NewEST == EST_MSAny && OldNR == FunctionProtoType::NR_Throw)
return false;
// As described above, noexcept(false) matches no spec only for functions.
if (AllowNoexceptAllMatchWithNoSpec) {
if (OldEST == EST_None && NewNR == FunctionProtoType::NR_Throw)
return false;
if (NewEST == EST_None && OldNR == FunctionProtoType::NR_Throw)
return false;
// Any non-throwing specifications are compatible.
bool OldNonThrowing = OldNR == FunctionProtoType::NR_Nothrow ||
OldEST == EST_DynamicNone;
bool NewNonThrowing = NewNR == FunctionProtoType::NR_Nothrow ||
NewEST == EST_DynamicNone;
if (OldNonThrowing && NewNonThrowing)
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;
// At this point, the only remaining valid case is two matching dynamic
// specifications. We return here unless both specifications are dynamic.
if (OldEST != EST_Dynamic || NewEST != EST_Dynamic) {
if (MissingExceptionSpecification && Old->hasExceptionSpec() &&
!New->hasExceptionSpec()) {
// The old type has an exception specification of some sort, but
// the new type does not.
*MissingExceptionSpecification = true;
if (MissingEmptyExceptionSpecification && OldNonThrowing) {
// 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;
assert(OldEST == EST_Dynamic && NewEST == EST_Dynamic &&
"Exception compatibility logic error: non-dynamic spec slipped through.");
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))
Success = false;
Success = Success && OldTypes.size() == NewTypes.size();
if (Success) {
return false;
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);
/// 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 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();
// If superset contains everything, we're done.
if (SuperEST == EST_None || SuperEST == EST_MSAny)
return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
Subset, SubLoc);
// 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.
// We also shortcut checking if a noexcept expression was bad.
FunctionProtoType::NoexceptResult SuperNR =Superset->getNoexceptSpec(Context);
if (SuperNR == FunctionProtoType::NR_BadNoexcept ||
SuperNR == FunctionProtoType::NR_Dependent)
return false;
// Another case of the superset containing everything.
if (SuperNR == FunctionProtoType::NR_Throw)
return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
Subset, SubLoc);
ExceptionSpecificationType SubEST = Subset->getExceptionSpecType();
assert(!isUnresolvedExceptionSpec(SuperEST) &&
!isUnresolvedExceptionSpec(SubEST) &&
"Shouldn't see unknown exception specifications here");
// It does not. If the subset contains everything, we've failed.
if (SubEST == EST_None || SubEST == EST_MSAny) {
Diag(SubLoc, DiagID);
if (NoteID.getDiagID() != 0)
Diag(SuperLoc, NoteID);
return true;
FunctionProtoType::NoexceptResult SubNR = Subset->getNoexceptSpec(Context);
if (SubNR == FunctionProtoType::NR_BadNoexcept ||
SubNR == FunctionProtoType::NR_Dependent)
return false;
// Another case of the subset containing everything.
if (SubNR == FunctionProtoType::NR_Throw) {
Diag(SubLoc, DiagID);
if (NoteID.getDiagID() != 0)
Diag(SuperLoc, NoteID);
return true;
// If the subset contains nothing, we're done.
if (SubEST == EST_DynamicNone || SubNR == FunctionProtoType::NR_Nothrow)
return CheckParamExceptionSpec(NestedDiagID, NoteID, Superset, SuperLoc,
Subset, SubLoc);
// Otherwise, if the superset contains nothing, we've failed.
if (SuperEST == EST_DynamicNone || SuperNR == FunctionProtoType::NR_Nothrow) {
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 (const auto &SubI : Subset->exceptions()) {
// Take one type from the subset.
QualType CanonicalSubT = Context.getCanonicalType(SubI);
// Unwrap pointers and references so that we can do checks within a class
// hierarchy. Don't unwrap member pointers; they don't have hierarchy
// conversions on the pointee.
bool SubIsPointer = false;
if (const ReferenceType *RefTy = CanonicalSubT->getAs<ReferenceType>())
CanonicalSubT = RefTy->getPointeeType();
if (const PointerType *PtrTy = CanonicalSubT->getAs<PointerType>()) {
CanonicalSubT = PtrTy->getPointeeType();
SubIsPointer = true;
bool SubIsClass = CanonicalSubT->isRecordType();
CanonicalSubT = CanonicalSubT.getLocalUnqualifiedType();
CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
bool Contained = false;
// Make sure it's in the superset.
for (const auto &SuperI : Superset->exceptions()) {
QualType CanonicalSuperT = Context.getCanonicalType(SuperI);
// SubT must be SuperT or derived from it, or pointer or reference to
// such types.
if (const ReferenceType *RefTy = CanonicalSuperT->getAs<ReferenceType>())
CanonicalSuperT = RefTy->getPointeeType();
if (SubIsPointer) {
if (const PointerType *PtrTy = CanonicalSuperT->getAs<PointerType>())
CanonicalSuperT = PtrTy->getPointeeType();
else {
CanonicalSuperT = CanonicalSuperT.getLocalUnqualifiedType();
// If the types are the same, move on to the next type in the subset.
if (CanonicalSubT == CanonicalSuperT) {
Contained = true;
// Otherwise we need to check the inheritance.
if (!SubIsClass || !CanonicalSuperT->isRecordType())
if (!IsDerivedFrom(SubLoc, CanonicalSubT, CanonicalSuperT, Paths))
if (Paths.isAmbiguous(Context.getCanonicalType(CanonicalSuperT)))
// Do this check from a context without privileges.
switch (CheckBaseClassAccess(SourceLocation(),
CanonicalSuperT, CanonicalSubT,
/*Diagnostic*/ 0,
/*ForceCheck*/ true,
/*ForceUnprivileged*/ true)) {
case AR_accessible: break;
case AR_inaccessible: continue;
case AR_dependent:
llvm_unreachable("access check dependent for unprivileged context");
case AR_delayed:
llvm_unreachable("access check delayed in non-declaration");
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().CPlusPlus1z) {
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(),
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;
if (getLangOpts().CPlusPlus11 && isa<CXXDestructorDecl>(New)) {
// Don't check uninstantiated template destructors at all. We can only
// synthesize correct specs after the template is instantiated.
if (New->getParent()->isDependentType())
return false;
if (New->getParent()->isBeingDefined()) {
// The destructor might be updated once the definition is finished. So
// remember it and check later.
DelayedExceptionSpecChecks.push_back(std::make_pair(New, Old));
return false;
// If the old exception specification hasn't been parsed yet, remember that
// we need to perform this check when we get to the end of the outermost
// lexically-surrounding class.
if (Old->getType()->castAs<FunctionProtoType>()->getExceptionSpecType() ==
EST_Unparsed) {
DelayedExceptionSpecChecks.push_back(std::make_pair(New, Old));
return false;
unsigned DiagID = diag::err_override_exception_spec;
if (getLangOpts().MicrosoftExt)
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().CPlusPlus1z && 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->getLocStart(), FT);
if (!FT)
return CT_Can;
return FT->isNothrow(S.Context) ? CT_Cannot : CT_Can;
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::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::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::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:
// 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