Commit 1b5404af authored by Richard Smith's avatar Richard Smith
Browse files

PR44540: Prefer an inherited default constructor over an initializer 

list constructor when initializing from {}.

We would previously pick between calling an initializer list constructor
and calling a default constructor unstably in this situation, depending
on whether the inherited default constructor had already been used
elsewhere in the program.
parent c6e69880

clang/lib/AST/DeclCXX.cpp

+43 −37
Original line number Diff line number Diff line
@@ -738,14 +738,19 @@ void CXXRecordDecl::addedMember(Decl *D) { 


  // Handle constructors.

  if (const auto *Constructor = dyn_cast<CXXConstructorDecl>(D)) {

    if (Constructor->isInheritingConstructor()) {

      // Ignore constructor shadow declarations. They are lazily created and

      // so shouldn't affect any properties of the class.

    } else {

      if (!Constructor->isImplicit()) {

        // Note that we have a user-declared constructor.

        data().UserDeclaredConstructor = true;



        // C++ [class]p4:

        //   A POD-struct is an aggregate class [...]

      // Since the POD bit is meant to be C++03 POD-ness, clear it even if the

      // type is technically an aggregate in C++0x since it wouldn't be in 03.

        // Since the POD bit is meant to be C++03 POD-ness, clear it even if

        // the type is technically an aggregate in C++0x since it wouldn't be

        // in 03.

        data().PlainOldData = false;

      }
@@ -782,6 +787,7 @@ void CXXRecordDecl::addedMember(Decl *D) { 
              : (Constructor->isUserProvided() || Constructor->isExplicit()))

        data().Aggregate = false;

    }

  }



  // Handle constructors, including those inherited from base classes.

  if (const auto *Constructor = dyn_cast<CXXConstructorDecl>(DUnderlying)) {

clang/lib/Sema/SemaInit.cpp

+2 −2
Original line number Diff line number Diff line
@@ -4059,7 +4059,7 @@ static void TryConstructorInitialization(Sema &S, 


    // If the initializer list has no elements and T has a default constructor,

    // the first phase is omitted.

    if (!(UnwrappedArgs.empty() && DestRecordDecl->hasDefaultConstructor()))

    if (!(UnwrappedArgs.empty() && S.LookupDefaultConstructor(DestRecordDecl)))

      Result = ResolveConstructorOverload(S, Kind.getLocation(), Args,

                                          CandidateSet, DestType, Ctors, Best,

                                          CopyInitialization, AllowExplicit,
@@ -4343,7 +4343,7 @@ static void TryListInitialization(Sema &S, 
      //     value-initialized.

      if (InitList->getNumInits() == 0) {

        CXXRecordDecl *RD = DestType->getAsCXXRecordDecl();

        if (RD->hasDefaultConstructor()) {

        if (S.LookupDefaultConstructor(RD)) {

          TryValueInitialization(S, Entity, Kind, Sequence, InitList);

          return;

        }

clang/test/CXX/dcl.decl/dcl.init/dcl.init.list/p3.cpp

+14 −0
Original line number Diff line number Diff line
@@ -86,6 +86,20 @@ namespace bullet6 { 
  const int& i1 = { 1 };

  const int& i2 = { 1.1 };  // expected-error {{type 'double' cannot be narrowed to 'int' in initializer list}} expected-note {{silence}} expected-warning {{implicit conversion}}

  const int (&iar)[2] = { 1, 2 };



  // We interpret "class type with a default constructor" as including the case

  // where a default constructor is inherited.

  struct X {

    X();

    X(std::initializer_list<int>) = delete;

  };

  struct Y : X {

    using X::X;

    Y(int);

  };

  Y y1{};

  void use() { Y y; }

  Y y2{};

}



namespace bullet7 {