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 16:53, Jason Merrill wrote:
> On Wed, Feb 28, 2018 at 9:36 AM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
> > in this P2 ICE on invalid we fail to diagnose an ill-formed variable
> > template partial specialization and the assert at the beginning of
> > determine_specialization triggers. Indeed, we didn't diagnose the problem
> > via check_specialization_scope (there are no template <>, thus
> > begin_specialization isn't involved). Simply adding a specific check to
> > check_explicit_specialization exactly when we recognize a variable template
> > partial specialization seems a safe thing to do and passes testing. Not sure
> > if the test itself is as simple as possible or is better done somewhere
> > else...
> Hmm, this doesn't look like the user intended to write a partial
> specialization, but rather that they were trying to define the member
> template and wrote the template arguments out by mistake.
I see your point. If I understand correctly, in such cases clang somehow 
talks about both possibilities:

error: variable template partial specialization does not specialize any 
template argument; to define the primary template, remove the template 
argument list

What do you think, should we do something similar? (by the way, 
yesterday got a bit confused because in other vaguely related cases 
clang also has this kind of two-part error message and we don't. Eg, I 
cooked up:

template <class T>
class Foo
{
  template <class U>
  class Bar;
};

template<class T>
template<class U>
class Foo<T>::Bar<U>;

Thanks,
Paolo.