c++/7584: Erroneous ambiguous base error on using declaration

[timb at bluearc dot com]

>Number:         7584
>Category:       c++
>Synopsis:       Erroneous ambiguous base error on using declaration
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Tue Aug 13 07:06:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     timb@bluearc.com
>Release:        3.1.1  (powerpc-eabi)
>Organization:
>Environment:
Debian GNU/Linux x86 unstable
>Description:
When compiling the code below, gcc reports "`A' is an ambiguous base of `C'" for each using declaration, and goes on to complain of "C::T x;" that "`typedef int A::T' is inaccessible". (Incidentally, the ambiguous base messages give the line number of the opening brace of the class definition.) There is no ambiguity for either using declaration, since A is a virtual base class. In the second, there would be no ambiguity even if A were a non-virtual base, since nested types can always be referred to unambiguously (para. 10.2/5).
>How-To-Repeat:
Compile the following with gcc -c

class A
{
public:
    typedef int T;
    int a;
};

class B : virtual private A
{
};

class C : virtual private A, public B
{
public:
    using A::a;
    using A::T;
};

C::T x;
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: