[Bug c++/89237] Partial specialization incorrectly marked as ambiguous

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89237

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-02-07
                 CC|                            |msebor at gcc dot gnu.org
     Ever confirmed|0                           |1
      Known to fail|                            |6.4.0, 7.3.0, 8.2.0, 9.0

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with the test case below (please be sure to include the compiler
output).  Not a regression.

Clang rejects it with the same error in C++ 98 mode so I wonder if the GCC
error is because of some yet-to-be implemented language change.

$ cat pr89237.C && /build/gcc-svn/gcc/xgcc -B /build/gcc-svn/gcc -S -Wall
pr89237.C
template <bool B, typename T = void> struct enable_if {};
template <typename T> struct enable_if<true, T> { typedef T type; };

template <typename T, typename = void> struct S;
template <typename T> struct S<T, typename enable_if<sizeof(T)>::type> {};
template <typename T> struct S<T *> {};

int main() { S<int *> s; }
pr89237.C: In function ‘int main()’:
pr89237.C:8:23: error: ambiguous template instantiation for ‘struct S<int*>’
    8 | int main() { S<int *> s; }
      |                       ^
pr89237.C:5:30: note: candidates are: ‘template<class T> struct S<T, typename
enable_if<(sizeof (T) != 0)>::type> [with T = int*]’
    5 | template <typename T> struct S<T, typename enable_if<sizeof(T)>::type>
{};
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr89237.C:6:30: note:                 ‘template<class T> struct S<T*> [with T =
int]’
    6 | template <typename T> struct S<T *> {};
      |                              ^~~~~~
pr89237.C:8:23: error: aggregate ‘S<int*> s’ has incomplete type and cannot be
defined
    8 | int main() { S<int *> s; }
      |                       ^