Re: [C++ Patch/RFC] PR 71569 ("[6/7/8 regression] Crash: External definition of template member from template struct")

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

On 28/02/2018 20:20, Jason Merrill wrote:
> Hmm, the test seems wrong; the diagnostic talks about specializing the
> arguments, but the actual test is checking whether the enclosing scope
> is fully specialized.  It looks like you'll give the same error for
>
> template <class T>
> struct A {
>    template <class U>
>    static const U u;
> };
>
> template <class T>
> template <class U>
> const U* A<T>::u<U*> = nullptr;
>
> which does specialize the argument; since we accept
>
> template <class T>
> struct A {
>    template <class U>
>    struct B;
> };
>
> template <class T>
> template <class U>
> struct A<T>::B<U*> { };
>
> we ought to accept the above as well.
>
> So, we could reject the testcase with this error, but we would need to
> test for it using the same check as in process_partial_specialization.
I see. Doing that seems relatively easy - I have a draft which appears 
to work - but then we have immediately to change the gcc_assert at the 
beginning of determine_specialization to let such specializations 
through (of course it still uses the wrong test!!). I'm not sure about 
the best way to do that... But that seems also doable. The next problem 
is duplicate_decls which apparently misses a bit of code to understand 
that the new declaration does not conflict with the old one near line 
#1650... So, frankly, I think that even with your great guidance I would 
need a few iterations to get right the whole package and we are so damn 
close to the release. What do you think? Do you want to take this over, 
or maybe you see us restricting a bit what we'll have working in this 
area for 8.1.0?

Thanks,
Paolo.