friend definition in nested class has private access to enclosing class

[llvmbot]

Bugzilla Link	31747
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor

Extended Description

Clang accepts ill-formed code in -std=c++11/14/1z:

struct Outer
{
    struct Inner
    {
        friend int get(Outer& o)
        {
            return o.x;
        }
    };
private:
    int x;
};

Legal basis (based on c++11 standard):
7.3.1.2[3], 11.3[6]: in-class friend function definition
is a namespace member
3.4.1[9], 11.3[7]: in-class friend function definition
has member function lexical scope
11.7[1]: in-nested-class function definition
can access private members of enclosing class
9.7[4]: in-nested-class friend function definition
has no special access rights to members of an enclosing class

It seems that explicit exception in 9.7[4] is not respected: "(...) friend function (...) has no special access rights to members of an enclosing class".
There's no warning with -Wall -Wextra -pedantic on clang-3.5, newer and trunk.

I'd expect compilation to fail with error. Other compilers (gcc, msvc, icc) fail as expected, noting that in given context x is private.

In c++98 code is ill-formed as well and clang incorrectly compiles it silently. In c++98 access from nested to enclosing class privates is illegal (11.8[1] c++03). In c++11 above clause was relaxed (11.7[1] c++11), but this shouldn't change the meaning of -std=c++98/03 in clang.

[shafik]

This is DR 1699

Which is also covers: #44053

Although not identical the resolution to DR 1699 should resolve all of these.

Also see cplusplus/papers#1573

[llvmbot]

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