[clang] [Clang] Implement diagnostics for why `std::is_standard_layout` is false (PR #144161)
Samarth Narang via cfe-commits
cfe-commits at lists.llvm.org
Wed Jun 25 06:21:57 PDT 2025
https://github.com/snarang181 updated https://github.com/llvm/llvm-project/pull/144161
>From 7f11d3392e3f3ead823c8af2ea9a3b1f9ef9e0c9 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Fri, 13 Jun 2025 23:22:18 +0200
Subject: [PATCH 1/9] Implement diagnostics for why `std::is_standard_layout`
is false
---
.../clang/Basic/DiagnosticSemaKinds.td | 9 +-
clang/lib/Sema/SemaTypeTraits.cpp | 132 ++++++++++++++++++
.../type-traits-unsatisfied-diags-std.cpp | 50 +++++++
.../SemaCXX/type-traits-unsatisfied-diags.cpp | 80 +++++++++++
4 files changed, 270 insertions(+), 1 deletion(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9392cbb39c021..232e1b94ee1da 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1767,7 +1767,8 @@ def note_unsatisfied_trait
: Note<"%0 is not %enum_select<TraitName>{"
"%TriviallyRelocatable{trivially relocatable}|"
"%Replaceable{replaceable}|"
- "%TriviallyCopyable{trivially copyable}"
+ "%TriviallyCopyable{trivially copyable}|"
+ "%StandardLayout{standard-layout}"
"}1">;
def note_unsatisfied_trait_reason
@@ -1787,6 +1788,12 @@ def note_unsatisfied_trait_reason
"%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}|"
+ "%NonStdLayoutBase{has a non-standard-layout base %1}|"
+ "%MixedAccess{has mixed access specifiers}|"
+ "%MultipleDataBase{has multiple base classes with data members}|"
+ "%VirtualFunction{has virtual functions}|"
+ "%NonStdLayoutMember{has a non-standard-layout member %1 of type %2}|"
+ "%IndirectBaseWithFields{has an indirect base %1 with data members}|"
"%DeletedDtr{has a %select{deleted|user-provided}1 destructor}|"
"%UserProvidedCtr{has a user provided %select{copy|move}1 "
"constructor}|"
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 4dbb2450857e0..9e34ea2fd5184 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -1956,6 +1956,7 @@ static std::optional<TypeTrait> StdNameToTypeTrait(StringRef Name) {
TypeTrait::UTT_IsCppTriviallyRelocatable)
.Case("is_replaceable", TypeTrait::UTT_IsReplaceable)
.Case("is_trivially_copyable", TypeTrait::UTT_IsTriviallyCopyable)
+ .Case("is_standard_layout", TypeTrait::UTT_IsStandardLayout)
.Default(std::nullopt);
}
@@ -2285,6 +2286,134 @@ static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
}
+static bool hasMixedAccessSpecifier(const CXXRecordDecl *D) {
+ AccessSpecifier FirstAccess = AS_none;
+ for (const FieldDecl *Field : D->fields()) {
+
+ if (Field->isUnnamedBitField())
+ continue;
+ AccessSpecifier FieldAccess = Field->getAccess();
+ if (FirstAccess == AS_none) {
+ FirstAccess = FieldAccess;
+ } else if (FieldAccess != FirstAccess) {
+ return true;
+ }
+ }
+ return false;
+}
+
+static bool hasMultipleDataBaseClassesWithFields(const CXXRecordDecl *D) {
+ int NumBasesWithFields = 0;
+ for (const CXXBaseSpecifier &Base : D->bases()) {
+ const CXXRecordDecl *BaseRD = Base.getType()->getAsCXXRecordDecl();
+ if (!BaseRD || BaseRD->isInvalidDecl())
+ continue;
+
+ for (const FieldDecl *Field : BaseRD->fields()) {
+ if (!Field->isUnnamedBitField()) {
+ ++NumBasesWithFields;
+ break; // Only count the base once.
+ }
+ }
+ }
+ return NumBasesWithFields > 1;
+}
+
+static void DiagnoseNonStandardLayoutReason(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 (!B.getType()->isStandardLayoutType()) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::NonStdLayoutBase << B.getType()
+ << B.getSourceRange();
+ }
+ }
+ if (hasMixedAccessSpecifier(D)) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::MixedAccess;
+ }
+ if (hasMultipleDataBaseClassesWithFields(D)) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::MultipleDataBase;
+ }
+ if (D->isPolymorphic()) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::VirtualFunction;
+ }
+ for (const FieldDecl *Field : D->fields()) {
+ if (!Field->getType()->isStandardLayoutType()) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::NonStdLayoutMember << Field
+ << Field->getType() << Field->getSourceRange();
+ }
+ }
+
+ // if this class and an indirect base
+ // both have non-static data members, grab the first such base.
+ if (D->hasDirectFields()) {
+ SmallVector<const CXXRecordDecl *, 4> Records;
+
+ // Recursive lambda to collect all bases that declare fields
+ std::function<void(const CXXRecordDecl *)> collect =
+ [&](const CXXRecordDecl *R) {
+ for (const CXXBaseSpecifier &B : R->bases()) {
+ const auto *BR = B.getType()->getAsCXXRecordDecl();
+ if (!BR || !BR->hasDefinition())
+ continue;
+ if (BR->hasDirectFields())
+ Records.push_back(BR);
+ // Recurse into the base class.
+ collect(BR);
+ }
+ };
+
+ // Collect all bases that declare fields.
+ collect(D);
+
+ // If more than one record has fields, then the layout is non-standard.
+ if (!Records.empty()) {
+ const CXXRecordDecl *Indirect = Records.front();
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::IndirectBaseWithFields << Indirect
+ << Indirect->getSourceRange();
+ }
+ }
+}
+
+static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
+ QualType T) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait)
+ << T << diag::TraitName::StandardLayout;
+
+ // Check type-level exclusion first
+ if (T->isVariablyModifiedType()) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::VLA;
+ return;
+ }
+
+ if (T->isReferenceType()) {
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::Ref;
+ return;
+ }
+ T = T.getNonReferenceType();
+ const CXXRecordDecl *D = T->getAsCXXRecordDecl();
+ if (!D || D->isInvalidDecl())
+ return;
+
+ if (D->hasDefinition())
+ DiagnoseNonStandardLayoutReason(SemaRef, Loc, D);
+
+ SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
+}
+
void Sema::DiagnoseTypeTraitDetails(const Expr *E) {
E = E->IgnoreParenImpCasts();
if (E->containsErrors())
@@ -2305,6 +2434,9 @@ void Sema::DiagnoseTypeTraitDetails(const Expr *E) {
case UTT_IsTriviallyCopyable:
DiagnoseNonTriviallyCopyableReason(*this, E->getBeginLoc(), Args[0]);
break;
+ case UTT_IsStandardLayout:
+ DiagnoseNonStandardLayoutReason(*this, E->getBeginLoc(), Args[0]);
+ break;
default:
break;
}
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp
index 329b611110c1d..59f3d95a4d215 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp
@@ -20,6 +20,13 @@ struct is_trivially_copyable {
template <typename T>
constexpr bool is_trivially_copyable_v = __is_trivially_copyable(T);
+
+template <typename T>
+struct is_standard_layout {
+static constexpr bool value = __is_standard_layout(T);
+};
+template <typename T>
+constexpr bool is_standard_layout_v = __is_standard_layout(T);
#endif
#ifdef STD2
@@ -44,6 +51,17 @@ using is_trivially_copyable = __details_is_trivially_copyable<T>;
template <typename T>
constexpr bool is_trivially_copyable_v = __is_trivially_copyable(T);
+
+template <typename T>
+struct __details_is_standard_layout {
+static constexpr bool value = __is_standard_layout(T);
+
+
+};
+template <typename T>
+using is_standard_layout = __details_is_standard_layout<T>;
+template <typename T>
+constexpr bool is_standard_layout_v = __is_standard_layout(T);
#endif
@@ -73,6 +91,13 @@ using is_trivially_copyable = __details_is_trivially_copyable<T>;
template <typename T>
constexpr bool is_trivially_copyable_v = is_trivially_copyable<T>::value;
+
+template <typename T>
+struct __details_is_standard_layout : bool_constant<__is_standard_layout(T)> {};
+template <typename T>
+using is_standard_layout = __details_is_standard_layout<T>;
+template <typename T>
+constexpr bool is_standard_layout_v = is_standard_layout<T>::value;
#endif
}
@@ -100,6 +125,21 @@ static_assert(std::is_trivially_copyable_v<int&>);
// expected-note at -1 {{because it is a reference type}}
+ // Direct tests
+ static_assert(std::is_standard_layout<int>::value);
+ static_assert(std::is_standard_layout_v<int>);
+
+ static_assert(std::is_standard_layout<int&>::value);
+ // expected-error-re at -1 {{static assertion failed due to requirement 'std::{{.*}}is_standard_layout<int &>::value'}} \
+ // expected-note at -1 {{'int &' is not standard-layout}} \
+ // expected-note at -1 {{because it is a reference type}}
+
+ static_assert(std::is_standard_layout_v<int&>);
+ // expected-error at -1 {{static assertion failed due to requirement 'std::is_standard_layout_v<int &>'}} \
+ // expected-note at -1 {{'int &' is not standard-layout}} \
+ // expected-note at -1 {{because it is a reference type}}
+
+
namespace test_namespace {
using namespace std;
static_assert(is_trivially_relocatable<int&>::value);
@@ -119,6 +159,16 @@ namespace test_namespace {
// expected-error at -1 {{static assertion failed due to requirement 'is_trivially_copyable_v<int &>'}} \
// expected-note at -1 {{'int &' is not trivially copyable}} \
// expected-note at -1 {{because it is a reference type}}
+
+ static_assert(is_standard_layout<int&>::value);
+ // expected-error-re at -1 {{static assertion failed due to requirement '{{.*}}is_standard_layout<int &>::value'}} \
+ // expected-note at -1 {{'int &' is not standard-layout}} \
+ // expected-note at -1 {{because it is a reference type}}
+
+ static_assert(is_standard_layout_v<int&>);
+ // expected-error at -1 {{static assertion failed due to requirement 'is_standard_layout_v<int &>'}} \
+ // expected-note at -1 {{'int &' is not standard-layout}} \
+ // expected-note at -1 {{because it is a reference type}}
}
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
index 5210354a66d43..128a69f0c413e 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
@@ -488,3 +488,83 @@ static_assert(__is_trivially_copyable(S12));
// expected-note at -1 {{'S12' is not trivially copyable}} \
// expected-note@#tc-S12 {{'S12' defined here}}
}
+
+namespace standard_layout_tests {
+struct WithVirtual { // #sl-Virtual
+ virtual void foo();
+};
+static_assert(__is_standard_layout(WithVirtual));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::WithVirtual)'}} \
+// expected-note at -1 {{'WithVirtual' is not standard-layout}} \
+// expected-note at -1 {{because it has virtual functions}} \
+// expected-note@#sl-Virtual {{'WithVirtual' defined here}}
+
+struct MixedAccess { // #sl-Mixed
+public:
+ int a;
+private:
+ int b;
+};
+static_assert(__is_standard_layout(MixedAccess));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::MixedAccess)'}} \
+// expected-note at -1 {{'MixedAccess' is not standard-layout}} \
+// expected-note at -1 {{because it has mixed access specifiers}} \
+// expected-note@#sl-Mixed {{'MixedAccess' defined here}}
+
+struct VirtualBase { virtual ~VirtualBase(); }; // #sl-VirtualBase
+struct VB : virtual VirtualBase {}; // #sl-VB
+static_assert(__is_standard_layout(VB));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::VB)'}} \
+// expected-note at -1 {{'VB' is not standard-layout}} \
+// expected-note at -1 {{because it has a virtual base 'VirtualBase'}} \
+// expected-note at -1 {{because it has a non-standard-layout base 'VirtualBase'}} \
+// expected-note at -1 {{because it has virtual functions}}
+// expected-note@#sl-VB {{'VB' defined here}}
+
+union U { // #sl-U
+public:
+ int x;
+private:
+ int y;
+};
+static_assert(__is_standard_layout(U));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::U)'}} \
+// expected-note at -1 {{'U' is not standard-layout}} \
+// expected-note at -1 {{because it has mixed access specifiers}}
+// expected-note@#sl-U {{'U' defined here}}
+
+// Single base class is OK
+struct BaseClass{ int a; }; // #sl-BaseClass
+struct DerivedOK : BaseClass {}; // #sl-DerivedOK
+static_assert(__is_standard_layout(DerivedOK));
+
+// Primitive types should be standard layout
+static_assert(__is_standard_layout(int)); // #sl-Int
+static_assert(__is_standard_layout(float)); // #sl-Float
+
+// Multi-level inheritance: Non-standard layout
+struct Base1 { int a; }; // #sl-Base1
+struct Base2 { int b; }; // #sl-Base2
+struct DerivedClass : Base1, Base2 {}; // #sl-DerivedClass
+static_assert(__is_standard_layout(DerivedClass));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::DerivedClass)'}} \
+// expected-note at -1 {{'DerivedClass' is not standard-layout}} \
+// expected-note at -1 {{because it has multiple base classes with data members}} \
+// expected-note@#sl-DerivedClass {{'DerivedClass' defined here}}
+
+// Inheritance hierarchy with multiple classes having data members
+struct BaseA { int a; }; // #sl-BaseA
+struct BaseB : BaseA {}; // inherits BaseA, has no new members
+struct BaseC: BaseB { int c; }; // #sl-BaseC
+static_assert(__is_standard_layout(BaseC));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::BaseC)'}} \
+// expected-note at -1 {{'BaseC' is not standard-layout}} \
+// expected-note at -1 {{because it has an indirect base 'BaseA' with data members}} \
+// expected-note@#sl-BaseC {{'BaseC' defined here}} \
+// Multiple direct base classes with no data members --> standard layout
+struct BaseX {}; // #sl-BaseX
+struct BaseY {}; // #sl-BaseY
+struct MultiBase : BaseX, BaseY {}; // #sl-MultiBase
+static_assert(__is_standard_layout(MultiBase));
+
+ }
>From d2b293a7a23b61d70c2e55cb03661bc7fb75c350 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Sat, 14 Jun 2025 08:56:44 +0200
Subject: [PATCH 2/9] Replace hand-written recursion with forAllBases
---
clang/lib/Sema/SemaTypeTraits.cpp | 35 +++++++++----------------------
1 file changed, 10 insertions(+), 25 deletions(-)
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 9e34ea2fd5184..6504ea911e399 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2353,32 +2353,17 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
<< Field->getType() << Field->getSourceRange();
}
}
-
- // if this class and an indirect base
- // both have non-static data members, grab the first such base.
+ // find any indirect base classes that have fields
if (D->hasDirectFields()) {
- SmallVector<const CXXRecordDecl *, 4> Records;
-
- // Recursive lambda to collect all bases that declare fields
- std::function<void(const CXXRecordDecl *)> collect =
- [&](const CXXRecordDecl *R) {
- for (const CXXBaseSpecifier &B : R->bases()) {
- const auto *BR = B.getType()->getAsCXXRecordDecl();
- if (!BR || !BR->hasDefinition())
- continue;
- if (BR->hasDirectFields())
- Records.push_back(BR);
- // Recurse into the base class.
- collect(BR);
- }
- };
-
- // Collect all bases that declare fields.
- collect(D);
-
- // If more than one record has fields, then the layout is non-standard.
- if (!Records.empty()) {
- const CXXRecordDecl *Indirect = Records.front();
+ const CXXRecordDecl *Indirect = nullptr;
+ D->forallBases([&](const CXXRecordDecl *BaseDef) {
+ if (BaseDef->hasDirectFields()) {
+ Indirect = BaseDef;
+ return false; // stop traversal
+ }
+ return true; // continue to the next base
+ });
+ if (Indirect) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::IndirectBaseWithFields << Indirect
<< Indirect->getSourceRange();
>From 8f0a6a8f096abf74b0b4166c82b221c53b1eaa81 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Thu, 19 Jun 2025 09:35:11 +0200
Subject: [PATCH 3/9] Address PR suggestions - Part 1
---
clang/include/clang/Basic/DiagnosticSemaKinds.td | 2 +-
clang/lib/Sema/SemaTypeTraits.cpp | 16 ++++++++--------
2 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 232e1b94ee1da..984cf203b285c 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1791,7 +1791,7 @@ def note_unsatisfied_trait_reason
"%NonStdLayoutBase{has a non-standard-layout base %1}|"
"%MixedAccess{has mixed access specifiers}|"
"%MultipleDataBase{has multiple base classes with data members}|"
- "%VirtualFunction{has virtual functions}|"
+ "%VirtualFunction{has a virtual function}|"
"%NonStdLayoutMember{has a non-standard-layout member %1 of type %2}|"
"%IndirectBaseWithFields{has an indirect base %1 with data members}|"
"%DeletedDtr{has a %select{deleted|user-provided}1 destructor}|"
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 6504ea911e399..46e10d54eaff4 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2293,11 +2293,10 @@ static bool hasMixedAccessSpecifier(const CXXRecordDecl *D) {
if (Field->isUnnamedBitField())
continue;
AccessSpecifier FieldAccess = Field->getAccess();
- if (FirstAccess == AS_none) {
+ if (FirstAccess == AS_none)
FirstAccess = FieldAccess;
- } else if (FieldAccess != FirstAccess) {
+ else if (FieldAccess != FirstAccess)
return true;
- }
}
return false;
}
@@ -2311,12 +2310,13 @@ static bool hasMultipleDataBaseClassesWithFields(const CXXRecordDecl *D) {
for (const FieldDecl *Field : BaseRD->fields()) {
if (!Field->isUnnamedBitField()) {
- ++NumBasesWithFields;
- break; // Only count the base once.
+ if (++NumBasesWithFields > 1)
+ return true; // found more than one base class with fields
+ break; // no need to check further fields in this base class
}
}
}
- return NumBasesWithFields > 1;
+ return false;
}
static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
@@ -2353,7 +2353,7 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
<< Field->getType() << Field->getSourceRange();
}
}
- // find any indirect base classes that have fields
+ // Find any indirect base classes that have fields.
if (D->hasDirectFields()) {
const CXXRecordDecl *Indirect = nullptr;
D->forallBases([&](const CXXRecordDecl *BaseDef) {
@@ -2376,7 +2376,7 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
SemaRef.Diag(Loc, diag::note_unsatisfied_trait)
<< T << diag::TraitName::StandardLayout;
- // Check type-level exclusion first
+ // Check type-level exclusion first.
if (T->isVariablyModifiedType()) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::VLA;
>From fb70b44e06d51479c3f1ba5c6123859c96199d00 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Thu, 19 Jun 2025 10:58:48 +0200
Subject: [PATCH 4/9] Fix tests
---
clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
index 128a69f0c413e..14a00d1555842 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
@@ -496,7 +496,7 @@ struct WithVirtual { // #sl-Virtual
static_assert(__is_standard_layout(WithVirtual));
// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::WithVirtual)'}} \
// expected-note at -1 {{'WithVirtual' is not standard-layout}} \
-// expected-note at -1 {{because it has virtual functions}} \
+// expected-note at -1 {{because it has a virtual function}} \
// expected-note@#sl-Virtual {{'WithVirtual' defined here}}
struct MixedAccess { // #sl-Mixed
@@ -518,7 +518,7 @@ static_assert(__is_standard_layout(VB));
// expected-note at -1 {{'VB' is not standard-layout}} \
// expected-note at -1 {{because it has a virtual base 'VirtualBase'}} \
// expected-note at -1 {{because it has a non-standard-layout base 'VirtualBase'}} \
-// expected-note at -1 {{because it has virtual functions}}
+// expected-note at -1 {{because it has a virtual function}}
// expected-note@#sl-VB {{'VB' defined here}}
union U { // #sl-U
>From 8aa95e2d21a3708eceae0ee85fb7ea81c6bdd98a Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Thu, 19 Jun 2025 11:11:39 +0200
Subject: [PATCH 5/9] Add method-specific diagnostics to diagnose virtual
function failures
---
clang/lib/Sema/SemaTypeTraits.cpp | 7 +++++++
clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp | 4 +++-
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 46e10d54eaff4..46f461bc79091 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2345,6 +2345,13 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
if (D->isPolymorphic()) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::VirtualFunction;
+
+ for (const CXXMethodDecl *Method : D->methods()) {
+ if (Method->isVirtual()) {
+ SemaRef.Diag(Method->getLocation(), diag::note_defined_here) << Method;
+ break;
+ }
+ }
}
for (const FieldDecl *Field : D->fields()) {
if (!Field->getType()->isStandardLayoutType()) {
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
index 14a00d1555842..5d8994a6c868d 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
@@ -491,12 +491,13 @@ static_assert(__is_trivially_copyable(S12));
namespace standard_layout_tests {
struct WithVirtual { // #sl-Virtual
- virtual void foo();
+ virtual void foo(); // #sl-Virtual-Foo
};
static_assert(__is_standard_layout(WithVirtual));
// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::WithVirtual)'}} \
// expected-note at -1 {{'WithVirtual' is not standard-layout}} \
// expected-note at -1 {{because it has a virtual function}} \
+// expected-note@#sl-Virtual-Foo {{'foo' defined here}} \
// expected-note@#sl-Virtual {{'WithVirtual' defined here}}
struct MixedAccess { // #sl-Mixed
@@ -520,6 +521,7 @@ static_assert(__is_standard_layout(VB));
// expected-note at -1 {{because it has a non-standard-layout base 'VirtualBase'}} \
// expected-note at -1 {{because it has a virtual function}}
// expected-note@#sl-VB {{'VB' defined here}}
+// expected-note@#sl-VB {{'~VB' defined here}}
union U { // #sl-U
public:
>From 952535f107f967872a853483959b10037f0014b4 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Thu, 19 Jun 2025 11:28:04 +0200
Subject: [PATCH 6/9] MixedAccess specifier diagnostics improvement Diagnose
fields which have different access
---
.../clang/Basic/DiagnosticSemaKinds.td | 1 +
clang/lib/Sema/SemaTypeTraits.cpp | 21 +++++++++++++++++++
.../SemaCXX/type-traits-unsatisfied-diags.cpp | 12 +++++++----
3 files changed, 30 insertions(+), 4 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 984cf203b285c..ad93598888ce6 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1790,6 +1790,7 @@ def note_unsatisfied_trait_reason
"%NTCField{has a non-trivially-copyable member %1 of type %2}|"
"%NonStdLayoutBase{has a non-standard-layout base %1}|"
"%MixedAccess{has mixed access specifiers}|"
+ "%MixedAccessField{field %1 has a different access specifier than field %2}|"
"%MultipleDataBase{has multiple base classes with data members}|"
"%VirtualFunction{has a virtual function}|"
"%NonStdLayoutMember{has a non-standard-layout member %1 of type %2}|"
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 46f461bc79091..be07ef5e8faf6 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2337,6 +2337,27 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
if (hasMixedAccessSpecifier(D)) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
<< diag::TraitNotSatisfiedReason::MixedAccess;
+
+ const FieldDecl *FirstField = nullptr;
+ AccessSpecifier FirstAcc = AS_none;
+ for (const FieldDecl *F : D->fields()) {
+ if (F->isUnnamedBitField())
+ continue;
+ if (FirstField == nullptr) {
+ FirstField = F;
+ FirstAcc = F->getAccess();
+ } else if (F->getAccess() != FirstAcc) {
+ SemaRef.Diag(FirstField->getLocation(), diag::note_defined_here)
+ << FirstField;
+
+ SemaRef.Diag(F->getLocation(), diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::MixedAccessField
+ << F // %0: second field
+ << FirstField; // %1: first field
+ break;
+ }
+ }
+ return;
}
if (hasMultipleDataBaseClassesWithFields(D)) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
index 5d8994a6c868d..2c9f2cfa6f6cf 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
@@ -502,14 +502,16 @@ static_assert(__is_standard_layout(WithVirtual));
struct MixedAccess { // #sl-Mixed
public:
- int a;
+ int a; // #sl-MixedF1
private:
- int b;
+ int b; // #sl-MixedF2
};
static_assert(__is_standard_layout(MixedAccess));
// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::MixedAccess)'}} \
// expected-note at -1 {{'MixedAccess' is not standard-layout}} \
// expected-note at -1 {{because it has mixed access specifiers}} \
+// expected-note@#sl-MixedF1 {{'a' defined here}}
+// expected-note@#sl-MixedF2 {{field 'b' has a different access specifier than field 'a'}}
// expected-note@#sl-Mixed {{'MixedAccess' defined here}}
struct VirtualBase { virtual ~VirtualBase(); }; // #sl-VirtualBase
@@ -525,14 +527,16 @@ static_assert(__is_standard_layout(VB));
union U { // #sl-U
public:
- int x;
+ int x; // #sl-UF1
private:
- int y;
+ int y; // #sl-UF2
};
static_assert(__is_standard_layout(U));
// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::U)'}} \
// expected-note at -1 {{'U' is not standard-layout}} \
// expected-note at -1 {{because it has mixed access specifiers}}
+// expected-note@#sl-UF1 {{'x' defined here}}
+// expected-note@#sl-UF2 {{field 'y' has a different access specifier than field 'x'}}
// expected-note@#sl-U {{'U' defined here}}
// Single base class is OK
>From 1de5966a22f16600ef046268147e123430fbde18 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Thu, 19 Jun 2025 16:34:58 +0200
Subject: [PATCH 7/9] Remove misleading comment
---
clang/lib/Sema/SemaTypeTraits.cpp | 66 ++++++++-----------
.../SemaCXX/type-traits-unsatisfied-diags.cpp | 63 +++++++++++++++++-
2 files changed, 90 insertions(+), 39 deletions(-)
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index be07ef5e8faf6..46f62c440349a 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2286,21 +2286,6 @@ static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
}
-static bool hasMixedAccessSpecifier(const CXXRecordDecl *D) {
- AccessSpecifier FirstAccess = AS_none;
- for (const FieldDecl *Field : D->fields()) {
-
- if (Field->isUnnamedBitField())
- continue;
- AccessSpecifier FieldAccess = Field->getAccess();
- if (FirstAccess == AS_none)
- FirstAccess = FieldAccess;
- else if (FieldAccess != FirstAccess)
- return true;
- }
- return false;
-}
-
static bool hasMultipleDataBaseClassesWithFields(const CXXRecordDecl *D) {
int NumBasesWithFields = 0;
for (const CXXBaseSpecifier &Base : D->bases()) {
@@ -2334,30 +2319,37 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
<< B.getSourceRange();
}
}
- if (hasMixedAccessSpecifier(D)) {
- SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
- << diag::TraitNotSatisfiedReason::MixedAccess;
+ // Check for mixed access specifiers in fields.
+ const FieldDecl *FirstField = nullptr;
+ AccessSpecifier FirstAccess = AS_none;
- const FieldDecl *FirstField = nullptr;
- AccessSpecifier FirstAcc = AS_none;
- for (const FieldDecl *F : D->fields()) {
- if (F->isUnnamedBitField())
- continue;
- if (FirstField == nullptr) {
- FirstField = F;
- FirstAcc = F->getAccess();
- } else if (F->getAccess() != FirstAcc) {
- SemaRef.Diag(FirstField->getLocation(), diag::note_defined_here)
- << FirstField;
-
- SemaRef.Diag(F->getLocation(), diag::note_unsatisfied_trait_reason)
- << diag::TraitNotSatisfiedReason::MixedAccessField
- << F // %0: second field
- << FirstField; // %1: first field
- break;
- }
+ for (const FieldDecl *Field : D->fields()) {
+ if (Field->isUnnamedBitField())
+ continue;
+
+ // Record the first field we see
+ if (!FirstField) {
+ FirstField = Field;
+ FirstAccess = Field->getAccess();
+ continue;
+ }
+
+ // Check if the field has a different access specifier than the first one.
+ if (Field->getAccess() != FirstAccess) {
+ // Emit a diagnostic about mixed access specifiers.
+ SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::MixedAccess;
+
+ SemaRef.Diag(FirstField->getLocation(), diag::note_defined_here)
+ << FirstField;
+
+ SemaRef.Diag(Field->getLocation(), diag::note_unsatisfied_trait_reason)
+ << diag::TraitNotSatisfiedReason::MixedAccessField << Field
+ << FirstField;
+
+ // No need to check further fields, as we already found mixed access.
+ return;
}
- return;
}
if (hasMultipleDataBaseClassesWithFields(D)) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
index 2c9f2cfa6f6cf..4ece45808e533 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wno-vla-cxx-extension -Wno-c++26-extensions -std=c++20 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-vla-cxx-extension -Wno-c++26-extensions -std=c++20 -fms-extensions %s
struct S : A {}; // expected-error{{expected class name}}
@@ -573,4 +573,63 @@ struct BaseY {}; // #sl-BaseY
struct MultiBase : BaseX, BaseY {}; // #sl-MultiBase
static_assert(__is_standard_layout(MultiBase));
- }
+struct A {
+ int x;
+};
+
+struct B : A {
+};
+// Indirect base with data members
+struct C : B { int y; }; // #sl-C
+static_assert(__is_standard_layout(C));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::C)'}} \
+// expected-note at -1 {{'C' is not standard-layout}} \
+// expected-note at -1 {{because it has an indirect base 'A' with data members}} \
+// expected-note@#sl-C {{'C' defined here}}
+
+struct D {
+ union { int a; float b; };
+ }; // #sl-D
+static_assert(__is_standard_layout(D)); // no diagnostics
+
+// E inherits D but adds a new member
+struct E : D { int x; }; // #sl-E
+static_assert(__is_standard_layout(E));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::E)'}} \
+// expected-note at -1 {{'E' is not standard-layout}} \
+// expected-note at -1 {{because it has an indirect base 'D' with data members}} \
+// expected-note@#sl-E {{'E' defined here}}
+
+// F inherits D but only an unnamed bitfield
+// This should still fail because F ends up with a
+// base class with a data member and its own unnamed bitfield
+// which is not allowed in standard layout
+struct F : D { int : 0; }; // #sl-F
+static_assert(__is_standard_layout(F));
+// expected-error at -1 {{static assertion failed due to requirement '__is_standard_layout(standard_layout_tests::F)'}} \
+// expected-note at -1 {{'F' is not standard-layout}} \
+// expected-note@#sl-F {{'F' defined here}}
+
+struct Empty {};
+struct G { Empty a, b; }; // #sl-G
+static_assert(__is_standard_layout(G)); // no diagnostics
+
+struct H { Empty a; int x; }; // #sl-H
+static_assert(__is_standard_layout(H)); // no diagnostics
+
+ struct I { Empty a; int : 0; int x; }; // #sl-I
+static_assert(__is_standard_layout(I)); // no diagnostics
+
+// [[no_unique_address]] or [[msvc::no_unique_address]] should not affect standard layout
+#if __has_cpp_attribute(no_unique_address)
+ #define NO_UNIQUE_ADDRESS [[no_unique_address]]
+#elif __has_cpp_attribute(msvc::no_unique_address)
+ #define NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]
+#elif defined(_MSC_VER)
+ #define NO_UNIQUE_ADDRESS __declspec(no_unique_address)
+#else
+ #define NO_UNIQUE_ADDRESS /* nothing */
+#endif
+struct J { NO_UNIQUE_ADDRESS Empty a; int x; };
+static_assert(__is_standard_layout(J)); // no diagnostics
+}
>From 5ca99e4acf7afa2463265d7b75d35fec5e9b37e6 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Wed, 25 Jun 2025 09:07:28 -0400
Subject: [PATCH 8/9] Address review comments: minor changes to tablegen
descriptions Revert note in ReleaseNotes Remove no_unique_address test
---
clang/include/clang/Basic/DiagnosticSemaKinds.td | 4 ++--
clang/lib/Sema/SemaTypeTraits.cpp | 4 ++--
.../test/SemaCXX/type-traits-unsatisfied-diags.cpp | 14 +-------------
3 files changed, 5 insertions(+), 17 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index ad93598888ce6..e3ab3d63a0779 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1788,12 +1788,12 @@ def note_unsatisfied_trait_reason
"%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}|"
- "%NonStdLayoutBase{has a non-standard-layout base %1}|"
+ "%NonStandardLayoutBase{has a non-standard-layout base %1}|"
"%MixedAccess{has mixed access specifiers}|"
"%MixedAccessField{field %1 has a different access specifier than field %2}|"
"%MultipleDataBase{has multiple base classes with data members}|"
"%VirtualFunction{has a virtual function}|"
- "%NonStdLayoutMember{has a non-standard-layout member %1 of type %2}|"
+ "%NonStandardLayoutMember{has a non-standard-layout member %1 of type %2}|"
"%IndirectBaseWithFields{has an indirect base %1 with data members}|"
"%DeletedDtr{has a %select{deleted|user-provided}1 destructor}|"
"%UserProvidedCtr{has a user provided %select{copy|move}1 "
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 46f62c440349a..1611e588c9b17 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2315,7 +2315,7 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
}
if (!B.getType()->isStandardLayoutType()) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
- << diag::TraitNotSatisfiedReason::NonStdLayoutBase << B.getType()
+ << diag::TraitNotSatisfiedReason::NonStandardLayoutBase << B.getType()
<< B.getSourceRange();
}
}
@@ -2369,7 +2369,7 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
for (const FieldDecl *Field : D->fields()) {
if (!Field->getType()->isStandardLayoutType()) {
SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
- << diag::TraitNotSatisfiedReason::NonStdLayoutMember << Field
+ << diag::TraitNotSatisfiedReason::NonStandardLayoutMember << Field
<< Field->getType() << Field->getSourceRange();
}
}
diff --git a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
index 4ece45808e533..56d974556365b 100644
--- a/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
+++ b/clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
@@ -619,17 +619,5 @@ static_assert(__is_standard_layout(H)); // no diagnostics
struct I { Empty a; int : 0; int x; }; // #sl-I
static_assert(__is_standard_layout(I)); // no diagnostics
-
-// [[no_unique_address]] or [[msvc::no_unique_address]] should not affect standard layout
-#if __has_cpp_attribute(no_unique_address)
- #define NO_UNIQUE_ADDRESS [[no_unique_address]]
-#elif __has_cpp_attribute(msvc::no_unique_address)
- #define NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]
-#elif defined(_MSC_VER)
- #define NO_UNIQUE_ADDRESS __declspec(no_unique_address)
-#else
- #define NO_UNIQUE_ADDRESS /* nothing */
-#endif
-struct J { NO_UNIQUE_ADDRESS Empty a; int x; };
-static_assert(__is_standard_layout(J)); // no diagnostics
}
+
>From 7d6b60899419a1f10509a15b5a0e58a487b8dfed Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Wed, 25 Jun 2025 09:21:15 -0400
Subject: [PATCH 9/9] The return should be a break
---
clang/lib/Sema/SemaTypeTraits.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index d246e21eb11cd..ccf596edbd98e 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -2376,7 +2376,7 @@ static void DiagnoseNonStandardLayoutReason(Sema &SemaRef, SourceLocation Loc,
<< FirstField;
// No need to check further fields, as we already found mixed access.
- return;
+ break;
}
}
if (hasMultipleDataBaseClassesWithFields(D)) {
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