[clang] Fix overly aggressive lifetime checks for parenthesized aggregate initialization

Before this patch, initialized class members would have the LifetimeKind
LK_MemInitializer, which does not allow for binding a temporary to a
reference. Binding to a temporary however is allowed in parenthesized
aggregate initialization, even if it leads to a dangling reference. To
fix this, we create a new EntityKind, EK_ParenAggInitMember, which has
LifetimeKind LK_FullExpression.

This patch does *not* attempt to diagnose dangling references as a
result of using this feature.

This patch also refactors TryOrBuildParenListInitialization(...) to
accomodate creating different InitializedEntity objects.

Fixes #61567

[0]: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0960r3.html

Reviewed By: shafik

Differential Revision: https://reviews.llvm.org/D148274

Author: alanzhao1

clang/docs/ReleaseNotes.rst

@@ -824,6 +824,9 @@ Bug Fixes to C++ Support
 - Fix default member initializers sometimes being ignored when performing
   parenthesized aggregate initialization of templated types.
   (`#62266 <https://github.com/llvm/llvm-project/issues/62266>`_)
+- Fix overly aggressive lifetime checks for parenthesized aggregate
+  initialization.
+  (`#61567 <https://github.com/llvm/llvm-project/issues/61567>`_)
 
 Concepts Specific Fixes:
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2124,7 +2124,8 @@ def err_init_conversion_failed : Error<
   "exception object|a member subobject|an array element|a new value|a value|a "
   "base class|a constructor delegation|a vector element|a block element|a "
   "block element|a complex element|a lambda capture|a compound literal "
-  "initializer|a related result|a parameter of CF audited function}0 "
+  "initializer|a related result|a parameter of CF audited function|a "
+  "structured binding|a member subobject}0 "
   "%diff{of type $ with an %select{rvalue|lvalue}2 of type $|"
   "with an %select{rvalue|lvalue}2 of incompatible type}1,3"
   "%select{|: different classes%diff{ ($ vs $)|}5,6"

clang/include/clang/Sema/Initialization.h

@@ -123,6 +123,10 @@ class alignas(8) InitializedEntity {
     /// decomposition declaration.
     EK_Binding,
 
+    /// The entity being initialized is a non-static data member subobject of an
+    /// object initialized via parenthesized aggregate initialization.
+    EK_ParenAggInitMember,
+
     // Note: err_init_conversion_failed in DiagnosticSemaKinds.td uses this
     // enum as an index for its first %select.  When modifying this list,
     // that diagnostic text needs to be updated as well.
@@ -227,8 +231,10 @@ class alignas(8) InitializedEntity {
 
   /// Create the initialization entity for a member subobject.
   InitializedEntity(FieldDecl *Member, const InitializedEntity *Parent,
-                    bool Implicit, bool DefaultMemberInit)
-      : Kind(EK_Member), Parent(Parent), Type(Member->getType()),
+                    bool Implicit, bool DefaultMemberInit,
+                    bool IsParenAggInit = false)
+      : Kind(IsParenAggInit ? EK_ParenAggInitMember : EK_Member),
+        Parent(Parent), Type(Member->getType()),
         Variable{Member, Implicit, DefaultMemberInit} {}
 
   /// Create the initialization entity for an array element.
@@ -388,6 +394,14 @@ class alignas(8) InitializedEntity {
     return InitializedEntity(Member->getAnonField(), Parent, Implicit, false);
   }
 
+  /// Create the initialization entity for a member subobject initialized via
+  /// parenthesized aggregate init.
+  static InitializedEntity InitializeMemberFromParenAggInit(FieldDecl *Member) {
+    return InitializedEntity(Member, /*Parent=*/nullptr, /*Implicit=*/false,
+                             /*DefaultMemberInit=*/false,
+                             /*IsParenAggInit=*/true);
+  }
+
   /// Create the initialization entity for a default member initializer.
   static InitializedEntity
   InitializeMemberFromDefaultMemberInitializer(FieldDecl *Member) {

clang/lib/Sema/SemaAccess.cpp

@@ -1651,7 +1651,8 @@ Sema::AccessResult Sema::CheckConstructorAccess(SourceLocation UseLoc,
        << Entity.getBaseSpecifier()->getType() << getSpecialMember(Constructor);
     break;
 
-  case InitializedEntity::EK_Member: {
+  case InitializedEntity::EK_Member:
+  case InitializedEntity::EK_ParenAggInitMember: {
     const FieldDecl *Field = cast<FieldDecl>(Entity.getDecl());
     PD = PDiag(diag::err_access_field_ctor);
     PD << Field->getType() << getSpecialMember(Constructor);