[cfe-dev] Patch to correct compilation errors related to class friend declarations

[Tom Honermann]

On 11/5/2011 3:05 AM, John McCall wrote:
> On Nov 4, 2011, at 8:34 PM, Tom Honermann wrote:
>> I checked out cfe/trunk today and attempted a build using an older
>> gcc compiler (4.0.3) on Linux.  The build failed in a few places
>> with the errors below.  The attached patch corrects these.  Each of
>> the errors was related to class friend declarations.
>>
>> llvm-trunk/tools/clang/include/clang/Basic/Diagnostic.h:590: error: 'clang::DiagnosticsEngine::<anonymous enum> clang::DiagnosticsEngine::MaxArguments' is private
>> llvm-trunk/tools/clang/include/clang/Basic/PartialDiagnostic.h:36: error: within this context
>> llvm-trunk/tools/clang/include/clang/Basic/Diagnostic.h:621: error: 'clang::DiagnosticsEngine::<anonymous enum> clang::DiagnosticsEngine::MaxFixItHints' is private
>> llvm-trunk/tools/clang/include/clang/Basic/PartialDiagnostic.h:68: error: within this context
>>
>> This error looks legit to me.  The code appears to be violating
>> C++03 11.4.2 [class.friend] and 11.8.1 [class.access.nest].
>> Granting friendship to a class does not confer friendship to nested
>> classes of the befriended class.
>
> It does, actually: [class.access]p2: A member of a class can also
> access all the names to which the class has access.
> [class.access.nest]p1: A nested class is a member and as such has the
> same access rights as any other member. It's the other way that
> doesn't hold;  having access to a class doesn't give you access to
> its nested classes.

It looks like you are quoting from C++11 (or draft) and that the 
behavior has changed from C++03 (or, there was a CWG defect related to 
this?).  C++03 11.4.2 [class.friend] and 11.8.1 [class.access.nest] are 
explicit that friendship does not confer to nested classes of a 
befriended class.  The example from C++03 11.4.2 is:

     class A {
         class B { };
         friend class X;
     };
     class X : A::B {      // ill-formed: A::B cannot be accessed
                           // in the base-clause for X
         A::B mx;          // OK: A::B used to declare member of X
         class Y : A::B {  // OK: A::B used to declare member of X
             A::B my;      // ill-formed: A::B cannot be accessed
                           // to declare members of nested class of X
         };
     };

C++03 11.8.1 states: "The members of a nested class have no special 
access to members of an enclosing class, nor to classes or functions 
that have granted friendship to an enclosing class"

Tom.