r258768 - [Sema] Incomplete types are OK for covariant returns

[David Majnemer via cfe-commits]

On Sunday, January 31, 2016, Kim Gräsman <kim.grasman at gmail.com> wrote:

> Hi David,
>
> Should this be guarded by if(cxx14)? I think the complete type was
> required by earlier standards.
>

It is the same issue as CWG defect report 1250:
http://wg21.cmeerw.net/cwg/issue1250

I forget how to tell how far back a DR applies but I'd guess this one goes
as far back as C++11.


> - Kim
> Den 26 jan 2016 2:40 fm skrev "David Majnemer via cfe-commits" <
> cfe-commits at lists.llvm.org
> <javascript:_e(%7B%7D,'cvml','cfe-commits at lists.llvm.org');>>:
>
>> Author: majnemer
>> Date: Mon Jan 25 19:37:01 2016
>> New Revision: 258768
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=258768&view=rev
>> Log:
>> [Sema] Incomplete types are OK for covariant returns
>>
>> Per C++14 [class.virtual]p8, it is OK for the return type's class type
>> to be incomplete so long as the return type is the same between the base
>> and complete classes.
>>
>> This fixes PR26297.
>>
>> Modified:
>>     cfe/trunk/lib/Sema/SemaDeclCXX.cpp
>>     cfe/trunk/test/SemaCXX/virtual-override.cpp
>>
>> Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=258768&r1=258767&r2=258768&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Mon Jan 25 19:37:01 2016
>> @@ -13020,19 +13020,20 @@ bool Sema::CheckOverridingFunctionReturn
>>      return true;
>>    }
>>
>> -  // C++ [class.virtual]p6:
>> -  //   If the return type of D::f differs from the return type of B::f,
>> the
>> -  //   class type in the return type of D::f shall be complete at the
>> point of
>> -  //   declaration of D::f or shall be the class type D.
>> -  if (const RecordType *RT = NewClassTy->getAs<RecordType>()) {
>> -    if (!RT->isBeingDefined() &&
>> -        RequireCompleteType(New->getLocation(), NewClassTy,
>> -                            diag::err_covariant_return_incomplete,
>> -                            New->getDeclName()))
>> -    return true;
>> -  }
>> -
>>    if (!Context.hasSameUnqualifiedType(NewClassTy, OldClassTy)) {
>> +    // C++14 [class.virtual]p8:
>> +    //   If the class type in the covariant return type of D::f differs
>> from
>> +    //   that of B::f, the class type in the return type of D::f shall be
>> +    //   complete at the point of declaration of D::f or shall be the
>> class
>> +    //   type D.
>> +    if (const RecordType *RT = NewClassTy->getAs<RecordType>()) {
>> +      if (!RT->isBeingDefined() &&
>> +          RequireCompleteType(New->getLocation(), NewClassTy,
>> +                              diag::err_covariant_return_incomplete,
>> +                              New->getDeclName()))
>> +        return true;
>> +    }
>> +
>>      // Check if the new class derives from the old class.
>>      if (!IsDerivedFrom(New->getLocation(), NewClassTy, OldClassTy)) {
>>        Diag(New->getLocation(), diag::err_covariant_return_not_derived)
>>
>> Modified: cfe/trunk/test/SemaCXX/virtual-override.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/virtual-override.cpp?rev=258768&r1=258767&r2=258768&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/virtual-override.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/virtual-override.cpp Mon Jan 25 19:37:01 2016
>> @@ -289,3 +289,15 @@ namespace PR8168 {
>>      static void foo() {} // expected-error{{'static' member function
>> 'foo' overrides a virtual function}}
>>    };
>>  }
>> +
>> +namespace PR26297 {
>> +struct Incomplete;
>> +
>> +struct Base {
>> +  virtual const Incomplete *meow() = 0;
>> +};
>> +
>> +struct Derived : Base {
>> +  virtual Incomplete *meow() override { return nullptr; }
>> +};
>> +}
>>
>>
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