Error "weak declaration must be public" with C++ const

[Alexey Salmin]

Hello!

I'm a bit puzzled with the g++ behavior which looks inconsistent.
Consider the following C++ code:

extern const int x; // typically comes from a header file
const int x = 0;

It produces a global symbol with g++ even though in C++ "const" on
variables implies "static". The definition inherits the "extern"
specifier from the declaration. So far so good.

Now if you need to provide a weak definition it won't compile:

extern const int x;
const int __attribute__((weak)) x = 0;

error: weak declaration of ‘x’ must be public

Adding "extern" to the second line fixes it. It's not clear why g++
considers the definition to be public in the first case (strong def)
and private in the second (weak def). Both cases work fine in clang++.

Is it a bug in g++?

Another question: even with a strong symbol, it's not completely clear
whether omitting "extern" on the second line produces a valid C++ code
(it certainly does for plain C). Standard states that using "extern"
and "static" in different declarations of the same symbol is an error.
However, there's no mention of "const" in that section, so I'm not
sure how these two work together.

Thank you,
Alexey