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[Clang] Explain why a type is not replaceable. #143265

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Jun 9, 2025
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[Clang] Explain why a type is not replaceable. #143265

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20 changes: 16 additions & 4 deletions clang/include/clang/Basic/DiagnosticSemaKinds.td
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Original file line number Diff line number Diff line change
Expand Up @@ -1763,27 +1763,39 @@ def err_user_defined_msg_constexpr : Error<
"constant expression">;

// Type traits explanations
def note_unsatisfied_trait : Note<"%0 is not %enum_select<TraitName>{"
"%TriviallyRelocatable{trivially relocatable}|"
"%TriviallyCopyable{trivially copyable}"
"}1">;
def note_unsatisfied_trait
: Note<"%0 is not %enum_select<TraitName>{"
"%TriviallyRelocatable{trivially relocatable}|"
"%Replaceable{replaceable}|"
"%TriviallyCopyable{trivially copyable}"
"}1">;

def note_unsatisfied_trait_reason
: Note<"because it "
"%enum_select<TraitNotSatisfiedReason>{"
"%Ref{is a reference type}|"
"%Const{is const}|"
"%Volatile{is volatile}|"
"%HasArcLifetime{has an ARC lifetime qualifier}|"
"%VLA{is a variably-modified type}|"
"%VBase{has a virtual base %1}|"
"%NotScalarOrClass{not %select{a|an array of objects of}1 scalar or "
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I don't see a test for the an array of objects case

"class type}|"
"%NTRBase{has a non-trivially-relocatable base %1}|"
"%NTRField{has a non-trivially-relocatable member %1 of type %2}|"
"%NonReplaceableBase{has a non-replaceable base %1}|"
"%NonReplaceableField{has a non-replaceable member %1 of type %2}|"
"%NTCBase{has a non-trivially-copyable base %1}|"
"%NTCField{has a non-trivially-copyable member %1 of type %2}|"
"%DeletedDtr{has a %select{deleted|user-provided}1 destructor}|"
"%UserProvidedCtr{has a user provided %select{copy|move}1 "
"constructor}|"
"%DeletedCtr{has a deleted %select{copy|move}1 "
"constructor}|"
"%UserProvidedAssign{has a user provided %select{copy|move}1 "
"assignment operator}|"
"%DeletedAssign{has a deleted %select{copy|move}1 "
"assignment operator}|"
"%UnionWithUserDeclaredSMF{is a union with a user-declared "
"%sub{select_special_member_kind}1}"
"}0">;
Expand Down
159 changes: 128 additions & 31 deletions clang/lib/Sema/SemaTypeTraits.cpp
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Expand Up @@ -104,6 +104,7 @@ static CXXMethodDecl *LookupSpecialMemberFromXValue(Sema &SemaRef,
OverloadCandidateSet::iterator Best;
switch (OCS.BestViableFunction(SemaRef, LookupLoc, Best)) {
case OR_Success:
case OR_Deleted:
return cast<CXXMethodDecl>(Best->Function);
default:
return nullptr;
Expand All @@ -120,7 +121,8 @@ static bool hasSuitableConstructorForRelocation(Sema &SemaRef,

CXXMethodDecl *Decl =
LookupSpecialMemberFromXValue(SemaRef, D, /*Assign=*/false);
return Decl && Decl->isUserProvided() == AllowUserDefined;
return Decl && Decl->isUserProvided() == AllowUserDefined &&
!Decl->isDeleted();
}

static bool hasSuitableMoveAssignmentOperatorForRelocation(
Expand All @@ -135,7 +137,8 @@ static bool hasSuitableMoveAssignmentOperatorForRelocation(
if (!Decl)
return false;

return Decl && Decl->isUserProvided() == AllowUserDefined;
return Decl && Decl->isUserProvided() == AllowUserDefined &&
!Decl->isDeleted();
}

// [C++26][class.prop]
Expand Down Expand Up @@ -1940,6 +1943,7 @@ static std::optional<TypeTrait> StdNameToTypeTrait(StringRef Name) {
return llvm::StringSwitch<std::optional<TypeTrait>>(Name)
.Case("is_trivially_relocatable",
TypeTrait::UTT_IsCppTriviallyRelocatable)
.Case("is_replaceable", TypeTrait::UTT_IsReplaceable)
.Case("is_trivially_copyable", TypeTrait::UTT_IsTriviallyCopyable)
.Default(std::nullopt);
}
Expand Down Expand Up @@ -2005,35 +2009,8 @@ static ExtractedTypeTraitInfo ExtractTypeTraitFromExpression(const Expr *E) {
return std::nullopt;
}

static void DiagnoseNonTriviallyRelocatableReason(Sema &SemaRef,
SourceLocation Loc,
const CXXRecordDecl *D) {
for (const CXXBaseSpecifier &B : D->bases()) {
assert(B.getType()->getAsCXXRecordDecl() && "invalid base?");
if (B.isVirtual())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::VBase << B.getType()
<< B.getSourceRange();
if (!SemaRef.IsCXXTriviallyRelocatableType(B.getType()))
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NTRBase << B.getType()
<< B.getSourceRange();
}
for (const FieldDecl *Field : D->fields()) {
if (!Field->getType()->isReferenceType() &&
!SemaRef.IsCXXTriviallyRelocatableType(Field->getType()))
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NTRField << Field
<< Field->getType() << Field->getSourceRange();
}
if (D->hasDeletedDestructor())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::DeletedDtr << /*Deleted*/ 0
<< D->getDestructor()->getSourceRange();

if (D->hasAttr<TriviallyRelocatableAttr>())
return;

static void DiagnoseNonDefaultMovable(Sema &SemaRef, SourceLocation Loc,
const CXXRecordDecl *D) {
if (D->isUnion()) {
auto DiagSPM = [&](CXXSpecialMemberKind K, bool Has) {
if (Has)
Expand Down Expand Up @@ -2074,6 +2051,37 @@ static void DiagnoseNonTriviallyRelocatableReason(Sema &SemaRef,
<< Dtr->getSourceRange();
}

static void DiagnoseNonTriviallyRelocatableReason(Sema &SemaRef,
SourceLocation Loc,
const CXXRecordDecl *D) {
for (const CXXBaseSpecifier &B : D->bases()) {
assert(B.getType()->getAsCXXRecordDecl() && "invalid base?");
if (B.isVirtual())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::VBase << B.getType()
<< B.getSourceRange();
if (!SemaRef.IsCXXTriviallyRelocatableType(B.getType()))
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NTRBase << B.getType()
<< B.getSourceRange();
}
for (const FieldDecl *Field : D->fields()) {
if (!Field->getType()->isReferenceType() &&
!SemaRef.IsCXXTriviallyRelocatableType(Field->getType()))
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NTRField << Field
<< Field->getType() << Field->getSourceRange();
}
if (D->hasDeletedDestructor())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::DeletedDtr << /*Deleted*/ 0
<< D->getDestructor()->getSourceRange();

if (D->hasAttr<TriviallyRelocatableAttr>())
return;
DiagnoseNonDefaultMovable(SemaRef, Loc, D);
}

static void DiagnoseNonTriviallyRelocatableReason(Sema &SemaRef,
SourceLocation Loc,
QualType T) {
Expand Down Expand Up @@ -2102,6 +2110,92 @@ static void DiagnoseNonTriviallyRelocatableReason(Sema &SemaRef,
SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
}

static void DiagnoseNonReplaceableReason(Sema &SemaRef, SourceLocation Loc,
const CXXRecordDecl *D) {
for (const CXXBaseSpecifier &B : D->bases()) {
assert(B.getType()->getAsCXXRecordDecl() && "invalid base?");
if (!SemaRef.IsCXXReplaceableType(B.getType()))
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NonReplaceableBase << B.getType()
<< B.getSourceRange();
}
for (const FieldDecl *Field : D->fields()) {
if (!SemaRef.IsCXXReplaceableType(Field->getType()))
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NonReplaceableField << Field
<< Field->getType() << Field->getSourceRange();
}
if (D->hasDeletedDestructor())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::DeletedDtr << /*Deleted*/ 0
<< D->getDestructor()->getSourceRange();

if (!D->hasSimpleMoveConstructor() && !D->hasSimpleCopyConstructor()) {
const auto *Decl = cast<CXXConstructorDecl>(
LookupSpecialMemberFromXValue(SemaRef, D, /*Assign=*/false));
if (Decl && Decl->isDeleted())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::DeletedCtr
<< Decl->isMoveConstructor() << Decl->getSourceRange();
}
if (!D->hasSimpleMoveAssignment() && !D->hasSimpleCopyAssignment()) {
CXXMethodDecl *Decl =
LookupSpecialMemberFromXValue(SemaRef, D, /*Assign=*/true);
if (Decl && Decl->isDeleted())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::DeletedAssign
<< Decl->isMoveAssignmentOperator() << Decl->getSourceRange();
}

if (D->hasAttr<ReplaceableAttr>())
return;
DiagnoseNonDefaultMovable(SemaRef, Loc, D);
}

static void DiagnoseNonReplaceableReason(Sema &SemaRef, SourceLocation Loc,
QualType T) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait)
<< T << diag::TraitName::Replaceable;

if (T->isVariablyModifiedType())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::VLA;

if (T->isReferenceType())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::Ref;
T = T.getNonReferenceType();

if (T.isConstQualified())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::Const;

if (T.isVolatileQualified())
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::Volatile;

bool IsArray = T->isArrayType();
T = SemaRef.getASTContext().getBaseElementType(T.getUnqualifiedType());

if (T->isScalarType())
return;

const CXXRecordDecl *D = T->getAsCXXRecordDecl();
if (!D) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::NotScalarOrClass << IsArray;
return;
}

if (D->isInvalidDecl())
return;

if (D->hasDefinition())
DiagnoseNonReplaceableReason(SemaRef, Loc, D);

SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
}

static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
SourceLocation Loc,
const CXXRecordDecl *D) {
Expand Down Expand Up @@ -2192,6 +2286,9 @@ void Sema::DiagnoseTypeTraitDetails(const Expr *E) {
case UTT_IsCppTriviallyRelocatable:
DiagnoseNonTriviallyRelocatableReason(*this, E->getBeginLoc(), Args[0]);
break;
case UTT_IsReplaceable:
DiagnoseNonReplaceableReason(*this, E->getBeginLoc(), Args[0]);
break;
case UTT_IsTriviallyCopyable:
DiagnoseNonTriviallyCopyableReason(*this, E->getBeginLoc(), Args[0]);
break;
Expand Down
25 changes: 25 additions & 0 deletions clang/test/SemaCXX/cxx2c-trivially-relocatable.cpp
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Expand Up @@ -333,6 +333,31 @@ struct CopyAssign1 {
CopyAssign1 & operator=(CopyAssign1 const &) = default;
};

struct UserDeleted1 {
UserDeleted1(const UserDeleted1&) = delete;
};
static_assert(!__builtin_is_cpp_trivially_relocatable(UserDeleted1));
static_assert(!__builtin_is_replaceable(UserDeleted1));

struct UserDeleted2 {
UserDeleted2(UserDeleted2&&) = delete;
};
static_assert(!__builtin_is_cpp_trivially_relocatable(UserDeleted2));
static_assert(!__builtin_is_replaceable(UserDeleted2));


struct UserDeleted3 {
UserDeleted3 operator=(UserDeleted3);
};
static_assert(!__builtin_is_cpp_trivially_relocatable(UserDeleted3));
static_assert(!__builtin_is_replaceable(UserDeleted3));

struct UserDeleted4 {
UserDeleted4 operator=(UserDeleted4&&);
};
static_assert(!__builtin_is_cpp_trivially_relocatable(UserDeleted4));
static_assert(!__builtin_is_replaceable(UserDeleted4));

}


Expand Down
21 changes: 21 additions & 0 deletions clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp
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Expand Up @@ -171,3 +171,24 @@ void test() {
// expected-note@#concept4 {{because it is a reference type}}
}
}


namespace std {
template <typename T>
struct is_replaceable {
static constexpr bool value = __builtin_is_replaceable(T);
};

template <typename T>
constexpr bool is_replaceable_v = __builtin_is_replaceable(T);

}

static_assert(std::is_replaceable<int&>::value);
// expected-error@-1 {{static assertion failed due to requirement 'std::is_replaceable<int &>::value'}} \
// expected-note@-1 {{'int &' is not replaceable}} \
// expected-note@-1 {{because it is a reference type}}
static_assert(std::is_replaceable_v<int&>);
// expected-error@-1 {{static assertion failed due to requirement 'std::is_replaceable_v<int &>'}} \
// expected-note@-1 {{'int &' is not replaceable}} \
// expected-note@-1 {{because it is a reference type}}
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