[cfe-dev] Problem with C++11 template methods, friend, and namespaces

[don hinton via cfe-dev]

Hi Johnny:

Is this bug preventing you from compiling TAO with clang?

I don't have a fix, but was able to create a smaller test case -- perhaps
it'll help someone figure out what's going on.

#include <type_traits>

namespace FOO {
class T_base {};
class A : public T_base {};

template <typename T> struct o_r;

template <typename T,
          typename = typename std::enable_if<std::is_base_of<T_base,
T>::value>>
o_r<T> make_f();

template <typename T> class o_r final {
  template <typename _Tp1,
            typename = std::enable_if<std::is_convertible<_Tp1 *, T
*>::value>>
  explicit o_r(_Tp1 *) {}
public:
  template <typename _Tp1, typename NOT_INFERED> friend o_r<_Tp1> make_f();
};

template <typename T, typename> o_r<T> make_f() { return o_r<T>(new T()); }
} // namespace FOO

void foo() {
#ifdef BAD
  auto l1 = FOO::make_f<FOO::A>();
  auto l2 = FOO::make_f<FOO::A>(); // << second one fails.
#else
  auto l1 = FOO::make_f<FOO::A>();
  auto l2 = FOO::make_f<FOO::A, void>();
#endif
}

local:/Users/dhinton/fail $ ../tools/3.9.0/Debug/bin/clang++ -std=c++11 -c
f.cpp -DBAD
f.cpp:27:13: error: no matching function for call to 'make_f'
  auto l2 = FOO::make_f<FOO::A>(); // << second one fails.
            ^~~~~~~~~~~~~~~~~~~
f.cpp:18:67: note: candidate template ignored: couldn't infer template
argument 'NOT_INFERED'
  template <typename _Tp1, typename NOT_INFERED> friend o_r<_Tp1> make_f();
                                                                  ^
1 error generated.

hth...
don

On Fri, Feb 24, 2017 at 12:18 PM, Johnny Willemsen via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi,
>
> Thanks for the confirmation. We also assumed it as something valid, the
> code does compile with Visual Studio 2015, gcc, and Intel C++ but we do
> know that that is not a guarantee that it is valid C++. Hopefully
> someone can pick this up soon and get this issue resolved.
>
> Thanks!
>
> Johnny
>
> On 02/24/2017 07:39 PM, John Brawn wrote:
> > This does look like a valid bug, and I've put a comment in the Bugzilla
> > ticket. It looks like something is going wrong with the handling of
> > default template arguments when instantiating friend template
> declarations,
> > though where exactly in clang the bug is originating I haven't a clue.
> >
> > John
> >
> >> -----Original Message-----
> >> From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of
> >> Johnny Willemsen via cfe-dev
> >> Sent: 24 February 2017 15:27
> >> To: cfe-dev at lists.llvm.org
> >> Subject: [cfe-dev] Problem with C++11 template methods, friend, and
> >> namespaces
> >>
> >> Hi,
> >>
> >> We reported an issue when we combine template methods, friend, and
> >> namespace in 2014 and nothing happened with the report until now (see
> >> https://bugs.llvm.org//show_bug.cgi?id=20877). Could maybe one of the
> >> developers confirm/deny that this is an issue or are we assuming some
> >> incorrect C++11 code?
> >>
> >> Best regards,
> >>
> >> Johnny Willemsen
> >> _______________________________________________
> >> cfe-dev mailing list
> >> cfe-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20170224/f2e0e910/attachment.html>