[Bug c++/59701] New: A variadic alias template aliasing another variadic alias template doesn't work

["ville.voutilainen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59701

            Bug ID: 59701
           Summary: A variadic alias template aliasing another variadic
                    alias template doesn't work
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com

template<typename... Args> struct foo { };
template<typename T, typename... Args> using bar = foo<T, Args...>;
template<typename T, typename... Args> using baz = bar<Args..., T>;

int
main (int argc, char *argv[])
{

}

This gives

edoceo7.cpp: In substitution of ‘template<class T, class ... Args> using bar =
foo<T, Args ...> [with T = Args ...; Args = {<expression error>}]’:
edoceo7.cpp:3:66:   required from here
edoceo7.cpp:2:67: error: template argument 2 is invalid
 template<typename T, typename... Args> using bar = foo<T, Args...>;
                                                                   ^
Multiple clang versions accept the code. Some clang versions ICE on it, but
that's another matter. :)
>From gcc-bugs-return-439399-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Jan 06 15:35:33 2014
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From: "ville.voutilainen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59702] New: Infinite recursion in a late-specified return type of a function template
Date: Mon, 06 Jan 2014 15:35:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59702

            Bug ID: 59702
           Summary: Infinite recursion in a late-specified return type of
                    a function template
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com

struct A {};

template<typename>
int func (A) {
  return {};
}

template<typename T>
auto func () -> decltype (func<T> (A{})) {
  return {};
}

int
main (int argc, char *argv[])
{
  func<int> ();
}

Result:

edoceo8.cpp:9:39: error: template instantiation depth exceeds maximum of 900
(use -ftemplate-depth= to increase the maximum) substituting ‘template<class T>
decltype (func<T>(A{})) func() [with T = int]’
 auto func () -> decltype (func<T> (A{})) {
                                       ^
edoceo8.cpp:9:39:   recursively required by substitution of ‘template<class T>
decltype (func<T>(A{})) func() [with T = int]’
edoceo8.cpp:9:39:   required by substitution of ‘template<class T> decltype
(func<T>(A{})) func() [with T = int]’
edoceo8.cpp:16:14:   required from here

edoceo8.cpp: In function ‘int main(int, char**)’:
edoceo8.cpp:16:14: error: no matching function for call to ‘func()’
   func<int> ();
              ^
edoceo8.cpp:16:14: note: candidates are:
edoceo8.cpp:4:5: note: template<class> int func(A)
 int func (A) {
     ^
edoceo8.cpp:4:5: note:   template argument deduction/substitution failed:
edoceo8.cpp:16:14: note:   candidate expects 1 argument, 0 provided
   func<int> ();
              ^
edoceo8.cpp:9:6: note: template<class T> decltype (func<T>(A{})) func()
 auto func () -> decltype (func<T> (A{})) {
      ^
edoceo8.cpp:9:6: note:   substitution of deduced template arguments resulted in
errors seen above


It doesn't seem to me like the late-specified return type is even referring to
the return type of the latter function template.
>From gcc-bugs-return-439400-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Jan 06 15:44:12 2014
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From: "ville.voutilainen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59702] Infinite recursion in a late-specified return type of a function template
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY702

--- Comment #1 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
I forgot to mention that clang accepts the code.