[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

via cfe-commits cfe-commits at lists.llvm.org
Mon Oct 28 08:12:22 PDT 2024


https://github.com/higher-performance updated https://github.com/llvm/llvm-project/pull/102040

>From 7ea9d3dbb6ff74ca3f7f9b9a0c589e4a0a3366f2 Mon Sep 17 00:00:00 2001
From: higher-performance <higher.performance.github at gmail.com>
Date: Mon, 5 Aug 2024 15:04:19 -0400
Subject: [PATCH 1/3] Add Clang attribute to ensure that fields are initialized
 explicitly

---
 .../clang/AST/CXXRecordDeclDefinitionBits.def |  9 ++++
 clang/include/clang/AST/DeclCXX.h             |  5 ++
 clang/include/clang/Basic/Attr.td             |  8 ++++
 clang/include/clang/Basic/AttrDocs.td         | 29 ++++++++++++
 clang/include/clang/Basic/DiagnosticGroups.td |  1 +
 .../clang/Basic/DiagnosticSemaKinds.td        |  7 +++
 clang/lib/AST/DeclCXX.cpp                     | 24 ++++++++++
 clang/lib/Sema/SemaDeclAttr.cpp               |  7 +++
 clang/lib/Sema/SemaInit.cpp                   | 15 ++++++
 ...a-attribute-supported-attributes-list.test |  1 +
 clang/test/SemaCXX/uninitialized.cpp          | 46 +++++++++++++++++++
 11 files changed, 152 insertions(+)

diff --git a/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def b/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def
index 6620840df0ced2..54f28046c63ebb 100644
--- a/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def
+++ b/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def
@@ -119,6 +119,15 @@ FIELD(HasInitMethod, 1, NO_MERGE)
 /// within anonymous unions or structs.
 FIELD(HasInClassInitializer, 1, NO_MERGE)
 
+/// Custom attribute that is True if any field is marked as requiring explicit
+/// initialization with [[clang::requires_explicit_initialization]] in a type
+/// without a user-provided default constructor, or if this is the case for any
+/// base classes and/or member variables whose types are aggregates.
+///
+/// In this case, default-construction is diagnosed, as it would not explicitly
+/// initialize the field.
+FIELD(HasUninitializedExplicitInitFields, 1, NO_MERGE)
+
 /// True if any field is of reference type, and does not have an
 /// in-class initializer.
 ///
diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index 252e6e92564142..27994da80243d6 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -1152,6 +1152,11 @@ class CXXRecordDecl : public RecordDecl {
   /// structs).
   bool hasInClassInitializer() const { return data().HasInClassInitializer; }
 
+  bool hasUninitializedExplicitInitFields() const {
+    return !isUnion() && !hasUserProvidedDefaultConstructor() &&
+           data().HasUninitializedExplicitInitFields;
+  }
+
   /// Whether this class or any of its subobjects has any members of
   /// reference type which would make value-initialization ill-formed.
   ///
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 70fad60d4edbb5..fa7d1b8013d036 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -1861,6 +1861,14 @@ def Leaf : InheritableAttr {
   let SimpleHandler = 1;
 }
 
+def ExplicitInit : InheritableAttr {
+  let Spellings = [Clang<"requires_explicit_initialization", 0>];
+  let Subjects = SubjectList<[Field], ErrorDiag>;
+  let Documentation = [ExplicitInitDocs];
+  let LangOpts = [CPlusPlus];
+  let SimpleHandler = 1;
+}
+
 def LifetimeBound : DeclOrTypeAttr {
   let Spellings = [Clang<"lifetimebound", 0>];
   let Subjects = SubjectList<[ParmVar, ImplicitObjectParameter], ErrorDiag>;
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 546e5100b79dd9..625dff5b4b7aa9 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -1419,6 +1419,35 @@ is not specified.
   }];
 }
 
+def ExplicitInitDocs : Documentation {
+  let Category = DocCatField;
+  let Content = [{
+The ``clang::requires_explicit_initialization`` attribute indicates that the
+field of an aggregate must be initialized explicitly by users when the class
+is constructed. Its usage is invalid on non-aggregates.
+
+Example usage:
+
+.. code-block:: c++
+
+  struct some_aggregate {
+    int x;
+    int y [[clang::requires_explicit_initialization]];
+  };
+
+  some_aggregate create() {
+    return {.x = 1};  // error: y is not initialized explicitly
+  }
+
+This attribute is *not* a memory safety feature, and is *not* intended to guard
+against use of uninitialized memory.
+Rather, its intended use is in structs that represent "parameter objects", to
+allow extending them while ensuring that callers do not forget to specify
+values for newly added fields ("parameters").
+
+  }];
+}
+
 def NoUniqueAddressDocs : Documentation {
   let Category = DocCatField;
   let Content = [{
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 116ce7a04f66f7..3a8b13898e2cd0 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -787,6 +787,7 @@ def Trigraphs      : DiagGroup<"trigraphs">;
 def UndefinedReinterpretCast : DiagGroup<"undefined-reinterpret-cast">;
 def ReinterpretBaseClass : DiagGroup<"reinterpret-base-class">;
 def Unicode  : DiagGroup<"unicode">;
+def UninitializedExplicitInit : DiagGroup<"uninitialized-explicit-init">;
 def UninitializedMaybe : DiagGroup<"conditional-uninitialized">;
 def UninitializedSometimes : DiagGroup<"sometimes-uninitialized">;
 def UninitializedStaticSelfInit : DiagGroup<"static-self-init">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index ce08bd60f76449..6dc386135034d6 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2302,6 +2302,10 @@ def err_init_list_bad_dest_type : Error<
 def warn_cxx20_compat_aggregate_init_with_ctors : Warning<
   "aggregate initialization of type %0 with user-declared constructors "
   "is incompatible with C++20">, DefaultIgnore, InGroup<CXX20Compat>;
+def warn_cxx20_compat_requires_explicit_init_non_aggregate : Warning<
+  "explicit initialization of field %0 may not be enforced in C++20 as type %1 "
+  "will become a non-aggregate due to the presence of user-declared "
+  "constructors">, DefaultIgnore, InGroup<CXX20Compat>;
 def warn_cxx17_compat_aggregate_init_paren_list : Warning<
   "aggregate initialization of type %0 from a parenthesized list of values "
   "is a C++20 extension">, DefaultIgnore, InGroup<CXX20>;
@@ -2331,6 +2335,9 @@ def err_init_reference_member_uninitialized : Error<
   "reference member of type %0 uninitialized">;
 def note_uninit_reference_member : Note<
   "uninitialized reference member is here">;
+def warn_field_requires_explicit_init : Warning<
+  "field %0 is not explicitly initialized, but was marked as requiring "
+  "explicit initialization">, InGroup<UninitializedExplicitInit>;
 def warn_field_is_uninit : Warning<"field %0 is uninitialized when used here">,
   InGroup<Uninitialized>;
 def warn_base_class_is_uninit : Warning<
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 01143391edab40..d56374ead6d794 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -29,6 +29,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/AST/UnresolvedSet.h"
 #include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/DiagnosticSema.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangOptions.h"
@@ -81,6 +82,7 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       HasPrivateFields(false), HasProtectedFields(false),
       HasPublicFields(false), HasMutableFields(false), HasVariantMembers(false),
       HasOnlyCMembers(true), HasInitMethod(false), HasInClassInitializer(false),
+      HasUninitializedExplicitInitFields(false),
       HasUninitializedReferenceMember(false), HasUninitializedFields(false),
       HasInheritedConstructor(false), HasInheritedDefaultConstructor(false),
       HasInheritedAssignment(false),
@@ -1111,6 +1113,10 @@ void CXXRecordDecl::addedMember(Decl *D) {
     } else if (!T.isCXX98PODType(Context))
       data().PlainOldData = false;
 
+    if (Field->hasAttr<ExplicitInitAttr>() && !Field->hasInClassInitializer()) {
+      data().HasUninitializedExplicitInitFields = true;
+    }
+
     if (T->isReferenceType()) {
       if (!Field->hasInClassInitializer())
         data().HasUninitializedReferenceMember = true;
@@ -1362,6 +1368,10 @@ void CXXRecordDecl::addedMember(Decl *D) {
         if (!FieldRec->hasCopyAssignmentWithConstParam())
           data().ImplicitCopyAssignmentHasConstParam = false;
 
+        if (FieldRec->hasUninitializedExplicitInitFields() &&
+            FieldRec->isAggregate() && !Field->hasInClassInitializer())
+          data().HasUninitializedExplicitInitFields = true;
+
         if (FieldRec->hasUninitializedReferenceMember() &&
             !Field->hasInClassInitializer())
           data().HasUninitializedReferenceMember = true;
@@ -2148,6 +2158,20 @@ void CXXRecordDecl::completeDefinition(CXXFinalOverriderMap *FinalOverriders) {
   for (conversion_iterator I = conversion_begin(), E = conversion_end();
        I != E; ++I)
     I.setAccess((*I)->getAccess());
+
+  ASTContext &Context = getASTContext();
+  if (!Context.getLangOpts().CPlusPlus20 && isAggregate() &&
+      hasUserDeclaredConstructor()) {
+    // Diagnose any aggregate behavior changes in C++20
+    for (field_iterator I = field_begin(), E = field_end(); I != E; ++I) {
+      if (const auto *attr = I->getAttr<ExplicitInitAttr>()) {
+        Context.getDiagnostics().Report(
+            getLocation(),
+            diag::warn_cxx20_compat_requires_explicit_init_non_aggregate)
+            << attr->getRange() << Context.getRecordType(this);
+      }
+    }
+  }
 }
 
 bool CXXRecordDecl::mayBeAbstract() const {
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 14cc51cf89665a..6145db10aa4932 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -6014,6 +6014,10 @@ static void handleNoMergeAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   D->addAttr(NoMergeAttr::Create(S.Context, AL));
 }
 
+static void handleExplicitInitAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  D->addAttr(ExplicitInitAttr::Create(S.Context, AL));
+}
+
 static void handleNoUniqueAddressAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   D->addAttr(NoUniqueAddressAttr::Create(S.Context, AL));
 }
@@ -6919,6 +6923,9 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
   case ParsedAttr::AT_NoMerge:
     handleNoMergeAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_ExplicitInit:
+    handleExplicitInitAttr(S, D, AL);
+    break;
   case ParsedAttr::AT_NoUniqueAddress:
     handleNoUniqueAddressAttr(S, D, AL);
     break;
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 4d11f2a43fcc6b..e89d72e67d854e 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -743,6 +743,14 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
         ILE->updateInit(SemaRef.Context, Init, Filler);
       return;
     }
+
+    if (!VerifyOnly && Field->hasAttr<ExplicitInitAttr>()) {
+      SemaRef.Diag(ILE->getExprLoc(), diag::warn_field_requires_explicit_init)
+          << Field;
+      SemaRef.Diag(Field->getLocation(), diag::note_entity_declared_at)
+          << Field;
+    }
+
     // C++1y [dcl.init.aggr]p7:
     //   If there are fewer initializer-clauses in the list than there are
     //   members in the aggregate, then each member not explicitly initialized
@@ -4561,6 +4569,13 @@ static void TryConstructorInitialization(Sema &S,
 
   CXXConstructorDecl *CtorDecl = cast<CXXConstructorDecl>(Best->Function);
   if (Result != OR_Deleted) {
+    if (!IsListInit && Kind.getKind() == InitializationKind::IK_Default &&
+        DestRecordDecl != nullptr && DestRecordDecl->isAggregate() &&
+        DestRecordDecl->hasUninitializedExplicitInitFields()) {
+      S.Diag(Kind.getLocation(), diag::warn_field_requires_explicit_init)
+          << "in class";
+    }
+
     // C++11 [dcl.init]p6:
     //   If a program calls for the default initialization of an object
     //   of a const-qualified type T, T shall be a class type with a
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
index baa1816358b156..5cc220e193b28d 100644
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -77,6 +77,7 @@
 // CHECK-NEXT: EnumExtensibility (SubjectMatchRule_enum)
 // CHECK-NEXT: Error (SubjectMatchRule_function)
 // CHECK-NEXT: ExcludeFromExplicitInstantiation (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record)
+// CHECK-NEXT: ExplicitInit (SubjectMatchRule_field)
 // CHECK-NEXT: ExternalSourceSymbol ((SubjectMatchRule_record, SubjectMatchRule_enum, SubjectMatchRule_enum_constant, SubjectMatchRule_field, SubjectMatchRule_function, SubjectMatchRule_namespace, SubjectMatchRule_objc_category, SubjectMatchRule_objc_implementation, SubjectMatchRule_objc_interface, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property, SubjectMatchRule_objc_protocol, SubjectMatchRule_record, SubjectMatchRule_type_alias, SubjectMatchRule_variable))
 // CHECK-NEXT: FlagEnum (SubjectMatchRule_enum)
 // CHECK-NEXT: Flatten (SubjectMatchRule_function)
diff --git a/clang/test/SemaCXX/uninitialized.cpp b/clang/test/SemaCXX/uninitialized.cpp
index 8a640c9691b321..37cf6d1dd60c0a 100644
--- a/clang/test/SemaCXX/uninitialized.cpp
+++ b/clang/test/SemaCXX/uninitialized.cpp
@@ -1472,3 +1472,49 @@ template<typename T> struct Outer {
   };
 };
 Outer<int>::Inner outerinner;
+
+void aggregate() {
+  struct S {
+    [[clang::requires_explicit_initialization]] int x; // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}}
+    int y;
+    int z = 12;
+    [[clang::requires_explicit_initialization]] int q = 100; // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}}
+    static void foo(S) { }
+  };
+
+  struct D : S { // expected-warning {{not explicitly initialized}}
+    int f1;
+    int f2 [[clang::requires_explicit_initialization]]; // expected-note {{declared}} // expected-note {{declared}}
+  };
+
+  struct C {
+    [[clang::requires_explicit_initialization]] int w;
+    C() = default;  // Test pre-C++20 aggregates
+  };
+
+  S::foo(S{1, 2, 3, 4});
+  S::foo(S{.x = 100, .q = 100});
+  S::foo(S{.x = 100}); // expected-warning {{'q' is not explicitly initialized}}
+  S s{.x = 100, .q = 100};
+  (void)s;
+  S t{.q = 100}; // expected-warning {{'x' is not explicitly initialized}}
+  (void)t;
+  S *ptr1 = new S; // expected-warning {{not explicitly initialized}}
+  delete ptr1;
+  S *ptr2 = new S{.x = 100, .q = 100};
+  delete ptr2;
+#if __cplusplus >= 202002L
+  D a({}, 0); // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'f2' is not explicitly initialized}}
+  (void)a;
+#else
+  C a; // expected-warning {{not explicitly initialized}}
+  (void)a;
+#endif
+  D b{.f2 = 1}; // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'q' is not explicitly initialized}}
+  (void)b;
+  D c{.f1 = 5}; // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'q' is not explicitly initialized}} expected-warning {{'f2' is not explicitly initialized}}
+  c = {{}, 0}; // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'q' is not explicitly initialized}} expected-warning {{'f2' is not explicitly initialized}}
+  (void)c;
+  D d; // expected-warning {{not explicitly initialized}}  // expected-note {{constructor}}
+  (void)d;
+}

>From 93bbb04db40807a76d2ac65438509996f8844a59 Mon Sep 17 00:00:00 2001
From: higher-performance <higher.performance.github at gmail.com>
Date: Wed, 25 Sep 2024 13:28:46 -0400
Subject: [PATCH 2/3] Implement explicit field initialization checks in
 RecordDecl and make it work in both C and C++

---
 .../clang/AST/CXXRecordDeclDefinitionBits.def |   9 --
 clang/include/clang/AST/Decl.h                |   8 ++
 clang/include/clang/AST/DeclBase.h            |  13 ++-
 clang/include/clang/AST/DeclCXX.h             |   5 -
 clang/include/clang/Basic/Attr.td             |   3 +-
 clang/include/clang/Basic/AttrDocs.td         |  31 +++---
 .../clang/Basic/DiagnosticSemaKinds.td        |   8 +-
 clang/lib/AST/Decl.cpp                        |   8 +-
 clang/lib/AST/DeclCXX.cpp                     |  32 ++++--
 clang/lib/Sema/SemaDecl.cpp                   |   3 +
 clang/lib/Sema/SemaInit.cpp                   |  26 ++++-
 clang/lib/Serialization/ASTReaderDecl.cpp     |   1 +
 clang/lib/Serialization/ASTWriterDecl.cpp     |   4 +-
 clang/test/Sema/uninit-variables.c            |  11 ++
 clang/test/SemaCXX/uninitialized.cpp          | 100 ++++++++++++++----
 15 files changed, 196 insertions(+), 66 deletions(-)

diff --git a/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def b/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def
index 54f28046c63ebb..6620840df0ced2 100644
--- a/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def
+++ b/clang/include/clang/AST/CXXRecordDeclDefinitionBits.def
@@ -119,15 +119,6 @@ FIELD(HasInitMethod, 1, NO_MERGE)
 /// within anonymous unions or structs.
 FIELD(HasInClassInitializer, 1, NO_MERGE)
 
-/// Custom attribute that is True if any field is marked as requiring explicit
-/// initialization with [[clang::requires_explicit_initialization]] in a type
-/// without a user-provided default constructor, or if this is the case for any
-/// base classes and/or member variables whose types are aggregates.
-///
-/// In this case, default-construction is diagnosed, as it would not explicitly
-/// initialize the field.
-FIELD(HasUninitializedExplicitInitFields, 1, NO_MERGE)
-
 /// True if any field is of reference type, and does not have an
 /// in-class initializer.
 ///
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index 0600ecc4d14a18..111b5582a4848c 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -4269,6 +4269,14 @@ class RecordDecl : public TagDecl {
     RecordDeclBits.HasNonTrivialToPrimitiveCopyCUnion = V;
   }
 
+  bool hasUninitializedExplicitInitFields() const {
+    return RecordDeclBits.HasUninitializedExplicitInitFields;
+  }
+
+  void setHasUninitializedExplicitInitFields(bool V) {
+    RecordDeclBits.HasUninitializedExplicitInitFields = V;
+  }
+
   /// Determine whether this class can be passed in registers. In C++ mode,
   /// it must have at least one trivial, non-deleted copy or move constructor.
   /// FIXME: This should be set as part of completeDefinition.
diff --git a/clang/include/clang/AST/DeclBase.h b/clang/include/clang/AST/DeclBase.h
index ee662ed73d7e0e..81027cb036ebe3 100644
--- a/clang/include/clang/AST/DeclBase.h
+++ b/clang/include/clang/AST/DeclBase.h
@@ -1447,6 +1447,9 @@ class DeclContext {
   /// hasLazyLocalLexicalLookups, hasLazyExternalLexicalLookups
   friend class ASTWriter;
 
+protected:
+  enum { NumOdrHashBits = 25 };
+
   // We use uint64_t in the bit-fields below since some bit-fields
   // cross the unsigned boundary and this breaks the packing.
 
@@ -1668,6 +1671,14 @@ class DeclContext {
     LLVM_PREFERRED_TYPE(bool)
     uint64_t HasNonTrivialToPrimitiveCopyCUnion : 1;
 
+    /// True if any field is marked as requiring explicit initialization with
+    /// [[clang::requires_explicit_initialization]].
+    /// In C++, this is also set for types without a user-provided default
+    /// constructor, and is propagated from any base classes and/or member
+    /// variables whose types are aggregates.
+    LLVM_PREFERRED_TYPE(bool)
+    uint64_t HasUninitializedExplicitInitFields : 1;
+
     /// Indicates whether this struct is destroyed in the callee.
     LLVM_PREFERRED_TYPE(bool)
     uint64_t ParamDestroyedInCallee : 1;
@@ -1682,7 +1693,7 @@ class DeclContext {
 
     /// True if a valid hash is stored in ODRHash. This should shave off some
     /// extra storage and prevent CXXRecordDecl to store unused bits.
-    uint64_t ODRHash : 26;
+    uint64_t ODRHash : NumOdrHashBits;
   };
 
   /// Number of inherited and non-inherited bits in RecordDeclBitfields.
diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index 27994da80243d6..252e6e92564142 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -1152,11 +1152,6 @@ class CXXRecordDecl : public RecordDecl {
   /// structs).
   bool hasInClassInitializer() const { return data().HasInClassInitializer; }
 
-  bool hasUninitializedExplicitInitFields() const {
-    return !isUnion() && !hasUserProvidedDefaultConstructor() &&
-           data().HasUninitializedExplicitInitFields;
-  }
-
   /// Whether this class or any of its subobjects has any members of
   /// reference type which would make value-initialization ill-formed.
   ///
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index fa7d1b8013d036..7f9ec696fc8380 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -1862,10 +1862,9 @@ def Leaf : InheritableAttr {
 }
 
 def ExplicitInit : InheritableAttr {
-  let Spellings = [Clang<"requires_explicit_initialization", 0>];
+  let Spellings = [Clang<"requires_explicit_initialization", 1>];
   let Subjects = SubjectList<[Field], ErrorDiag>;
   let Documentation = [ExplicitInitDocs];
-  let LangOpts = [CPlusPlus];
   let SimpleHandler = 1;
 }
 
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 625dff5b4b7aa9..42c63c86093842 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -1426,24 +1426,31 @@ The ``clang::requires_explicit_initialization`` attribute indicates that the
 field of an aggregate must be initialized explicitly by users when the class
 is constructed. Its usage is invalid on non-aggregates.
 
-Example usage:
+Note that this attribute is *not* a memory safety feature, and is *not* intended
+to guard against use of uninitialized memory.
+
+Rather, it is intended for use in "parameter-objects", used to simulate the
+passing of named parameters.
+The attribute generates a warning when explicit initializers for such
+"named parameters" are not provided:
 
 .. code-block:: c++
 
-  struct some_aggregate {
-    int x;
-    int y [[clang::requires_explicit_initialization]];
+  struct ArrayIOParams {
+    size_t count [[clang::requires_explicit_initialization]];
+    size_t element_size [[clang::requires_explicit_initialization]];
+    int flags = 0;
   };
 
-  some_aggregate create() {
-    return {.x = 1};  // error: y is not initialized explicitly
-  }
+  size_t ReadArray(FILE *file, void *buffer, ArrayIOParams params);
 
-This attribute is *not* a memory safety feature, and is *not* intended to guard
-against use of uninitialized memory.
-Rather, its intended use is in structs that represent "parameter objects", to
-allow extending them while ensuring that callers do not forget to specify
-values for newly added fields ("parameters").
+  int main() {
+    unsigned int buf[512];
+    ReadArray(stdin, buf, {
+      .count = sizeof(buf) / sizeof(*buf),
+      // warning: field 'element_size' is not explicitly initialized
+    });
+  }
 
   }];
 }
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 6dc386135034d6..b75b10ed4e0952 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2336,8 +2336,8 @@ def err_init_reference_member_uninitialized : Error<
 def note_uninit_reference_member : Note<
   "uninitialized reference member is here">;
 def warn_field_requires_explicit_init : Warning<
-  "field %0 is not explicitly initialized, but was marked as requiring "
-  "explicit initialization">, InGroup<UninitializedExplicitInit>;
+  "field %select{%1|in %1}0 is not explicitly initialized, but was marked as "
+  "requiring explicit initialization">, InGroup<UninitializedExplicitInit>;
 def warn_field_is_uninit : Warning<"field %0 is uninitialized when used here">,
   InGroup<Uninitialized>;
 def warn_base_class_is_uninit : Warning<
@@ -3148,6 +3148,10 @@ def warn_attribute_ignored_no_calls_in_stmt: Warning<
   "statement">,
   InGroup<IgnoredAttributes>;
 
+def warn_attribute_needs_aggregate : Warning<
+  "%0 attribute is ignored in non-aggregate type %1">,
+  InGroup<IgnoredAttributes>;
+
 def warn_attribute_ignored_non_function_pointer: Warning<
   "%0 attribute is ignored because %1 is not a function pointer">,
   InGroup<IgnoredAttributes>;
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index a14b1b33d35efc..167f747f2fb297 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -5014,6 +5014,7 @@ RecordDecl::RecordDecl(Kind DK, TagKind TK, const ASTContext &C,
   setHasNonTrivialToPrimitiveDefaultInitializeCUnion(false);
   setHasNonTrivialToPrimitiveDestructCUnion(false);
   setHasNonTrivialToPrimitiveCopyCUnion(false);
+  setHasUninitializedExplicitInitFields(false);
   setParamDestroyedInCallee(false);
   setArgPassingRestrictions(RecordArgPassingKind::CanPassInRegs);
   setIsRandomized(false);
@@ -5214,9 +5215,10 @@ unsigned RecordDecl::getODRHash() {
   // Only calculate hash on first call of getODRHash per record.
   ODRHash Hash;
   Hash.AddRecordDecl(this);
-  // For RecordDecl the ODRHash is stored in the remaining 26
-  // bit of RecordDeclBits, adjust the hash to accomodate.
-  setODRHash(Hash.CalculateHash() >> 6);
+  // For RecordDecl the ODRHash is stored in the remaining
+  // bits of RecordDeclBits, adjust the hash to accommodate.
+  static_assert(sizeof(Hash.CalculateHash()) * CHAR_BIT == 32);
+  setODRHash(Hash.CalculateHash() >> (32 - NumOdrHashBits));
   return RecordDeclBits.ODRHash;
 }
 
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index d56374ead6d794..d261982b5d69a6 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -82,7 +82,6 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       HasPrivateFields(false), HasProtectedFields(false),
       HasPublicFields(false), HasMutableFields(false), HasVariantMembers(false),
       HasOnlyCMembers(true), HasInitMethod(false), HasInClassInitializer(false),
-      HasUninitializedExplicitInitFields(false),
       HasUninitializedReferenceMember(false), HasUninitializedFields(false),
       HasInheritedConstructor(false), HasInheritedDefaultConstructor(false),
       HasInheritedAssignment(false),
@@ -460,6 +459,10 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
     if (BaseClassDecl->hasMutableFields())
       data().HasMutableFields = true;
 
+    if (BaseClassDecl->hasUninitializedExplicitInitFields() &&
+        BaseClassDecl->isAggregate())
+      setHasUninitializedExplicitInitFields(true);
+
     if (BaseClassDecl->hasUninitializedReferenceMember())
       data().HasUninitializedReferenceMember = true;
 
@@ -1114,7 +1117,7 @@ void CXXRecordDecl::addedMember(Decl *D) {
       data().PlainOldData = false;
 
     if (Field->hasAttr<ExplicitInitAttr>() && !Field->hasInClassInitializer()) {
-      data().HasUninitializedExplicitInitFields = true;
+      setHasUninitializedExplicitInitFields(true);
     }
 
     if (T->isReferenceType()) {
@@ -1370,7 +1373,7 @@ void CXXRecordDecl::addedMember(Decl *D) {
 
         if (FieldRec->hasUninitializedExplicitInitFields() &&
             FieldRec->isAggregate() && !Field->hasInClassInitializer())
-          data().HasUninitializedExplicitInitFields = true;
+          setHasUninitializedExplicitInitFields(true);
 
         if (FieldRec->hasUninitializedReferenceMember() &&
             !Field->hasInClassInitializer())
@@ -2160,17 +2163,32 @@ void CXXRecordDecl::completeDefinition(CXXFinalOverriderMap *FinalOverriders) {
     I.setAccess((*I)->getAccess());
 
   ASTContext &Context = getASTContext();
-  if (!Context.getLangOpts().CPlusPlus20 && isAggregate() &&
-      hasUserDeclaredConstructor()) {
+
+  if (isAggregate() && hasUserDeclaredConstructor() &&
+      !Context.getLangOpts().CPlusPlus20) {
     // Diagnose any aggregate behavior changes in C++20
     for (field_iterator I = field_begin(), E = field_end(); I != E; ++I) {
       if (const auto *attr = I->getAttr<ExplicitInitAttr>()) {
         Context.getDiagnostics().Report(
-            getLocation(),
+            attr->getLocation(),
             diag::warn_cxx20_compat_requires_explicit_init_non_aggregate)
-            << attr->getRange() << Context.getRecordType(this);
+            << attr << Context.getRecordType(this);
+      }
+    }
+  }
+
+  if (!isAggregate() && hasUninitializedExplicitInitFields()) {
+    // Diagnose any fields that required explicit initialization in a
+    // non-aggregate type. (Note that the fields may not be directly in this
+    // type, but in a subobject. In such cases we don't emit diagnoses here.)
+    for (field_iterator I = field_begin(), E = field_end(); I != E; ++I) {
+      if (const auto *attr = I->getAttr<ExplicitInitAttr>()) {
+        Context.getDiagnostics().Report(attr->getLocation(),
+                                        diag::warn_attribute_needs_aggregate)
+            << attr << Context.getRecordType(this);
       }
     }
+    setHasUninitializedExplicitInitFields(false);
   }
 }
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 8557c25b93a8da..9a29214779c4ce 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -19086,6 +19086,9 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
         if (FT.hasNonTrivialToPrimitiveCopyCUnion() || Record->isUnion())
           Record->setHasNonTrivialToPrimitiveCopyCUnion(true);
       }
+      if (FD->hasAttr<ExplicitInitAttr>()) {
+        Record->setHasUninitializedExplicitInitFields(true);
+      }
       if (FT.isDestructedType()) {
         Record->setNonTrivialToPrimitiveDestroy(true);
         Record->setParamDestroyedInCallee(true);
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index e89d72e67d854e..b650c3f584e1da 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -268,6 +268,14 @@ static void CheckStringInit(Expr *Str, QualType &DeclT, const ArrayType *AT,
   updateStringLiteralType(Str, DeclT);
 }
 
+void emitUninitializedExplicitInitFields(Sema &S, const RecordDecl *R) {
+  for (const FieldDecl *Field : R->fields()) {
+    if (Field->hasAttr<ExplicitInitAttr>()) {
+      S.Diag(Field->getLocation(), diag::note_entity_declared_at) << Field;
+    }
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // Semantic checking for initializer lists.
 //===----------------------------------------------------------------------===//
@@ -746,7 +754,7 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
 
     if (!VerifyOnly && Field->hasAttr<ExplicitInitAttr>()) {
       SemaRef.Diag(ILE->getExprLoc(), diag::warn_field_requires_explicit_init)
-          << Field;
+          << /* Var-in-Record */ 0 << Field;
       SemaRef.Diag(Field->getLocation(), diag::note_entity_declared_at)
           << Field;
     }
@@ -4573,7 +4581,8 @@ static void TryConstructorInitialization(Sema &S,
         DestRecordDecl != nullptr && DestRecordDecl->isAggregate() &&
         DestRecordDecl->hasUninitializedExplicitInitFields()) {
       S.Diag(Kind.getLocation(), diag::warn_field_requires_explicit_init)
-          << "in class";
+          << /* Var-in-Record */ 1 << DestRecordDecl;
+      emitUninitializedExplicitInitFields(S, DestRecordDecl);
     }
 
     // C++11 [dcl.init]p6:
@@ -6472,6 +6481,19 @@ void InitializationSequence::InitializeFrom(Sema &S,
     }
   }
 
+  if (!S.getLangOpts().CPlusPlus &&
+      Kind.getKind() == InitializationKind::IK_Default) {
+    RecordDecl *Rec = DestType->getAsRecordDecl();
+    if (Rec && Rec->hasUninitializedExplicitInitFields()) {
+      VarDecl *Var = dyn_cast_or_null<VarDecl>(Entity.getDecl());
+      if (Var && !Initializer) {
+        S.Diag(Var->getLocation(), diag::warn_field_requires_explicit_init)
+            << /* Var-in-Record */ 1 << Rec;
+        emitUninitializedExplicitInitFields(S, Rec);
+      }
+    }
+  }
+
   //     - If the destination type is a reference type, see 8.5.3.
   if (DestType->isReferenceType()) {
     // C++0x [dcl.init.ref]p1:
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 9272e23c7da3fc..b53aa8a649ae6b 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -859,6 +859,7 @@ RedeclarableResult ASTDeclReader::VisitRecordDeclImpl(RecordDecl *RD) {
       RecordDeclBits.getNextBit());
   RD->setHasNonTrivialToPrimitiveDestructCUnion(RecordDeclBits.getNextBit());
   RD->setHasNonTrivialToPrimitiveCopyCUnion(RecordDeclBits.getNextBit());
+  RD->setHasUninitializedExplicitInitFields(RecordDeclBits.getNextBit());
   RD->setParamDestroyedInCallee(RecordDeclBits.getNextBit());
   RD->setArgPassingRestrictions(
       (RecordArgPassingKind)RecordDeclBits.getNextBits(/*Width=*/2));
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 555f6325da646b..92145831e4db64 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -574,6 +574,7 @@ void ASTDeclWriter::VisitRecordDecl(RecordDecl *D) {
   RecordDeclBits.addBit(D->hasNonTrivialToPrimitiveDefaultInitializeCUnion());
   RecordDeclBits.addBit(D->hasNonTrivialToPrimitiveDestructCUnion());
   RecordDeclBits.addBit(D->hasNonTrivialToPrimitiveCopyCUnion());
+  RecordDeclBits.addBit(D->hasUninitializedExplicitInitFields());
   RecordDeclBits.addBit(D->isParamDestroyedInCallee());
   RecordDeclBits.addBits(llvm::to_underlying(D->getArgPassingRestrictions()), 2);
   Record.push_back(RecordDeclBits);
@@ -2407,7 +2408,8 @@ void ASTWriter::WriteDeclAbbrevs() {
             // isNonTrivialToPrimitiveCopy, isNonTrivialToPrimitiveDestroy,
             // hasNonTrivialToPrimitiveDefaultInitializeCUnion,
             // hasNonTrivialToPrimitiveDestructCUnion,
-            // hasNonTrivialToPrimitiveCopyCUnion, isParamDestroyedInCallee,
+            // hasNonTrivialToPrimitiveCopyCUnion,
+            // hasUninitializedExplicitInitFields, isParamDestroyedInCallee,
             // getArgPassingRestrictions
   // ODRHash
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 26));
diff --git a/clang/test/Sema/uninit-variables.c b/clang/test/Sema/uninit-variables.c
index 70a00793fd29ed..d4f4686b600c40 100644
--- a/clang/test/Sema/uninit-variables.c
+++ b/clang/test/Sema/uninit-variables.c
@@ -551,3 +551,14 @@ struct full_of_empty empty_test_2(void) {
   struct full_of_empty e;
   return e; // no-warning
 }
+
+struct with_explicit_field {
+  int x;
+  int y [[clang::requires_explicit_initialization]]; // #FIELD_Y
+};
+
+void aggregate() {
+  struct with_explicit_field a; // expected-warning {{field in 'with_explicit_field' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_Y {{'y' declared here}}
+  struct with_explicit_field b = {1}; // expected-warning {{field 'y' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_Y {{'y' declared here}}
+  (void)(&a != &b);
+}
diff --git a/clang/test/SemaCXX/uninitialized.cpp b/clang/test/SemaCXX/uninitialized.cpp
index 37cf6d1dd60c0a..95e04cdfe5909a 100644
--- a/clang/test/SemaCXX/uninitialized.cpp
+++ b/clang/test/SemaCXX/uninitialized.cpp
@@ -1474,47 +1474,103 @@ template<typename T> struct Outer {
 Outer<int>::Inner outerinner;
 
 void aggregate() {
-  struct S {
-    [[clang::requires_explicit_initialization]] int x; // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}}
-    int y;
-    int z = 12;
-    [[clang::requires_explicit_initialization]] int q = 100; // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}} // expected-note {{declared}}
-    static void foo(S) { }
+  struct NonAgg {
+    NonAgg() { }
+    [[clang::requires_explicit_initialization]] int na;  // expected-warning {{'requires_explicit_initialization' attribute is ignored in non-aggregate type 'NonAgg'}}
   };
+  NonAgg nonagg;  // no-warning
+  (void)nonagg;
 
-  struct D : S { // expected-warning {{not explicitly initialized}}
-    int f1;
-    int f2 [[clang::requires_explicit_initialization]]; // expected-note {{declared}} // expected-note {{declared}}
+  struct S {
+    [[clang::requires_explicit_initialization]] int s1; // #FIELD_S1
+    int s2;
+    int s3 = 12;
+    [[clang::requires_explicit_initialization]] int s4 = 100; // #FIELD_S4
+    static void foo(S) { }
   };
 
   struct C {
-    [[clang::requires_explicit_initialization]] int w;
+    [[clang::requires_explicit_initialization]] int c1; // #FIELD_C1
     C() = default;  // Test pre-C++20 aggregates
   };
 
+  struct D : S { // #TYPE_D
+    int d1;
+    int d2 [[clang::requires_explicit_initialization]]; // #FIELD_D2
+  };
+
+  struct D2 : D {  // #TYPE_D2
+  };
+
+  struct E {  // #TYPE_E
+    int e1;
+    D e2 [[clang::requires_explicit_initialization]]; // #FIELD_E2
+    struct {
+      [[clang::requires_explicit_initialization]] D e3;
+      D2 e4 [[clang::requires_explicit_initialization]];
+    };
+  };
+
   S::foo(S{1, 2, 3, 4});
-  S::foo(S{.x = 100, .q = 100});
-  S::foo(S{.x = 100}); // expected-warning {{'q' is not explicitly initialized}}
-  S s{.x = 100, .q = 100};
+  S::foo(S{.s1 = 100, .s4 = 100});
+  S::foo(S{.s1 = 100}); // expected-warning {{field 's4' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S4 {{'s4' declared here}}
+
+  S s{.s1 = 100, .s4 = 100};
   (void)s;
-  S t{.q = 100}; // expected-warning {{'x' is not explicitly initialized}}
+
+  S t{.s4 = 100}; // expected-warning {{field 's1' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S1 {{'s1' declared here}}
   (void)t;
-  S *ptr1 = new S; // expected-warning {{not explicitly initialized}}
+
+  S *ptr1 = new S; // expected-warning {{field in 'S' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S4 {{'s4' declared here}} expected-note@#FIELD_S1 {{'s1' declared here}}
   delete ptr1;
-  S *ptr2 = new S{.x = 100, .q = 100};
+
+  S *ptr2 = new S{.s1 = 100, .s4 = 100};
   delete ptr2;
+
 #if __cplusplus >= 202002L
-  D a({}, 0); // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'f2' is not explicitly initialized}}
+  // expected-warning at +2 {{field 'd2' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_D2 {{'d2' declared here}}
+  // expected-warning {{field 's1' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S1 {{'s1' declared here}}
+  D a({}, 0);
   (void)a;
 #else
-  C a; // expected-warning {{not explicitly initialized}}
+  C a; // expected-warning {{field in 'C' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_C1 {{'c1' declared here}}
   (void)a;
 #endif
-  D b{.f2 = 1}; // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'q' is not explicitly initialized}}
+
+  // expected-warning at +2 {{field 's4' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S4 {{'s4' declared here}}
+  // expected-warning at +1 {{field 's1' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S1 {{'s1' declared here}}
+  D b{.d2 = 1};
   (void)b;
-  D c{.f1 = 5}; // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'q' is not explicitly initialized}} expected-warning {{'f2' is not explicitly initialized}}
-  c = {{}, 0}; // expected-warning {{'x' is not explicitly initialized}} expected-warning {{'q' is not explicitly initialized}} expected-warning {{'f2' is not explicitly initialized}}
+
+  // expected-warning at +3 {{field 's4' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S4 {{'s4' declared here}}
+  // expected-warning at +2 {{field 'd2' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_D2 {{'d2' declared here}}
+  // expected-warning at +1 {{field 's1' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S1 {{'s1' declared here}}
+  D c{.d1 = 5};
+
+  // expected-warning at +3 {{field 's4' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S4 {{'s4' declared here}}
+  // expected-warning at +2 {{field 'd2' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_D2 {{'d2' declared here}}
+  // expected-warning at +1 {{field 's1' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S1 {{'s1' declared here}}
+  c = {{}, 0};
   (void)c;
-  D d; // expected-warning {{not explicitly initialized}}  // expected-note {{constructor}}
+
+  // expected-note at +3 {{in implicit default constructor for 'D' first required here}}
+  // expected-warning@#TYPE_D {{field in 'S' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_S1 {{'s1' declared here}} expected-note@#FIELD_S4 {{'s4' declared here}}
+  // expected-warning at +1 {{field in 'D' is not explicitly initialized, but was marked as requiring explicit initialization}} expected-note@#FIELD_D2 {{'d2' declared here}}
+  D d;
   (void)d;
+
+  // expected-warning at +12 {{field in 'E' is not explicitly initialized, but was marked as requiring explicit initialization}}
+  // expected-note@#FIELD_E2 {{'e2' declared here}}
+  // expected-warning@#TYPE_E {{field in 'D' is not explicitly initialized, but was marked as requiring explicit initialization}}
+  // expected-note at +9 {{in implicit default constructor for 'E' first required here}}
+  // expected-note@#FIELD_D2 {{'d2' declared here}}
+  // expected-warning@#TYPE_E {{field in 'D' is not explicitly initialized, but was marked as requiring explicit initialization}}
+  // expected-note@#FIELD_D2 {{'d2' declared here}}
+  // expected-warning@#TYPE_E {{field in 'D2' is not explicitly initialized, but was marked as requiring explicit initialization}}
+  // expected-note@#TYPE_E {{in implicit default constructor for 'D2' first required here}}
+  // expected-warning@#TYPE_D2 {{field in 'D' is not explicitly initialized, but was marked as requiring explicit initialization}}
+  // expected-note at +2 {{in implicit default constructor for 'E' first required here}}
+  // expected-note@#FIELD_D2 {{'d2' declared here}}
+  E e;
+  (void)e;
 }

>From 6d07ac1d7a1a6b522f061e30595ba3f2d78fc366 Mon Sep 17 00:00:00 2001
From: higher-performance <github+google at me.tracemymail.com>
Date: Mon, 28 Oct 2024 11:12:11 -0400
Subject: [PATCH 3/3] Update clang/include/clang/Basic/Attr.td

Co-authored-by: Erich Keane <ekeane at nvidia.com>
---
 clang/include/clang/Basic/Attr.td | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 7f9ec696fc8380..61fb24f35bd00b 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -1862,7 +1862,7 @@ def Leaf : InheritableAttr {
 }
 
 def ExplicitInit : InheritableAttr {
-  let Spellings = [Clang<"requires_explicit_initialization", 1>];
+  let Spellings = [Clang<"requires_explicit_initialization">];
   let Subjects = SubjectList<[Field], ErrorDiag>;
   let Documentation = [ExplicitInitDocs];
   let SimpleHandler = 1;



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