[clang] Remove overly restrictive aggregate paren init logic

[ayzhao]

Summary

Previously, we would only attempt to perform a parenthesized aggregate
initialization if constructor initialization failed for only the default
constructor, default copy constructor, and default move constructor. The
original intent of this logic was to reject initializing objects that
have failed resolving a user-defined constructor. However, this check is
redundant because we check for isAggregate() before attempting to
perform a parenthesized aggregate initialization, and classes that have
user-defined or user-declared constructors are not aggregates.
Furthermore, this check is too restrictive - the following valid
examples fail:

• Aggregate class with user-defined destructor - fails because default move constructors are not generated for classes with user-defined destructors (https://github.com/llvm/llvm-project/issues/54040#issuecomment-1356926048)
• Concept-guarded conversion operator on an aggregate's member: (https://github.com/llvm/llvm-project/issues/54040#issuecomment-1356931745)

The solution therefore is to remove this logic; existing tests still
pass, and the previously failing examples now compile.

[ilya-biryukov]

LGTM

clang/lib/Sema/SemaInit.cpp

static bool canPerformArrayCopy(const InitializedEntity &Entity) {
 
   default:
     break;
   }
 
   return false;
 }
 
-static bool onlyHasDefaultedCtors(OverloadCandidateSet &OCS) {
-  if (OCS.size() != 3)
-    return false;
-
-  bool HasDefaultCtor = false, HasCopyCtor = false, HasMoveCtor = false;
-  for (const auto &Candidate : OCS) {
-    if (auto *Ctor = dyn_cast_or_null<CXXConstructorDecl>(Candidate.Function);
-        Ctor != nullptr && Ctor->isDefaulted()) {
-      if (Ctor->isDefaultConstructor())
-        HasDefaultCtor = true;
-      else if (Ctor->isCopyConstructor())
-        HasCopyCtor = true;
-      else if (Ctor->isMoveConstructor())
-        HasMoveCtor = true;
-    }
-  }
-  return HasDefaultCtor && HasCopyCtor && HasMoveCtor;
-}
-
 void InitializationSequence::InitializeFrom(Sema &S,
                                             const InitializedEntity &Entity,
                                             const InitializationKind &Kind,
                                             MultiExprArg Args,
                                             bool TopLevelOfInitList,
                                             bool TreatUnavailableAsInvalid) {
   ASTContext &Context = S.Context;
 
if (Kind.getKind() == InitializationKind::IK_Direct ||
                                    *this);
 
       // We fall back to the "no matching constructor" path if the
       // failed candidate set has functions other than the three default
       // constructors. For example, conversion function.
       if (const auto *RD =
               dyn_cast<CXXRecordDecl>(DestType->getAs<RecordType>()->getDecl());
           S.getLangOpts().CPlusPlus20 && RD && RD->isAggregate() && Failed() &&
-          getFailureKind() == FK_ConstructorOverloadFailed &&
-          onlyHasDefaultedCtors(getFailedCandidateSet())) {
+          getFailureKind() == FK_ConstructorOverloadFailed) {
         // C++20 [dcl.init] 17.6.2.2:
         //   - Otherwise, if no constructor is viable, the destination type is
         //   an
         //      aggregate class, and the initializer is a parenthesized
         //      expression-list.
         TryOrBuildParenListInitialization(S, Entity, Kind, Args, *this,
                                           /*VerifyOnly=*/true);
       }

clang/test/CodeGen/paren-list-agg-init.cpp

 // RUN: %clang_cc1 -std=c++20 %s -emit-llvm -triple x86_64-unknown-linux-gnu -o - | FileCheck %s
 
+template <typename T>
+struct IsChar {
+  constexpr operator bool() const { return false; }
+};
+
+template<>
+struct IsChar<char> {
+  constexpr operator bool() const { return true; }
+};
+
+template <typename T>
+concept SameAsChar = (bool)IsInt<T>();
+
 // CHECK-DAG: [[STRUCT_A:%.*]] = type { i8, double }
 struct A {
   char i;
   double j;
+
+  template <SameAsChar T>
+  operator T() const { return i; };
 };
 
 // CHECK-DAG: [[STRUCT_B:%.*]] = type { [[STRUCT_A]], i32 }
 struct B {
   A a;
   int b;
 };
 
struct D {
   unsigned : 2;
   A c;
 };
 
 // CHECK-DAG: [[STRUCT_E:%.*]] = type { i32, ptr }
 struct E {
   int a;
   const char* fn = __builtin_FUNCTION();
+  ~E() {};
 };
 
 // CHECK-DAG: [[STRUCT_F:%.*]] = type { i8 }
 struct F {
   F (int i = 1);
   F (const F &f) = delete;
   F (F &&f) = default;
 };