[Bug c++/77302] New: partial specialization marked as ambiguous

[rlangendam at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77302

            Bug ID: 77302
           Summary: partial specialization marked as ambiguous
           Product: gcc
           Version: 6.1.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rlangendam at gmail dot com
  Target Milestone: ---

Created attachment 39475
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39475&action=edit
C++ source file that wrongfully fails to compile

Compiling the attached C++ source file with g++ 6.1.1 20160802, as described
below, yields an ambiguity error wrongfully. After all, out of the two
mentioned partial specializations, the former is more specialized than the
latter. FYI, the file compiles fine using clang++ 3.8, using the same options.

$ g++ -std=c++11 -c test.cpp
test.cpp:15:64: error: ambiguous template instantiation for ‘struct
Test<std::integral_constant<int, 0> >’
 static_assert(std::is_same<Test<std::integral_constant<int, 0>>::type,
void>::value, "");
                                                                ^~
test.cpp:6:8: note: candidates are: template<class T> struct
Test<std::integral_constant<T, 0> > [with T = int]
 struct Test<std::integral_constant<T, 0>> {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:11:8: note:                 template<class T, T V> struct
Test<std::integral_constant<T, V> > [with T = int; T V = 0]
 struct Test<std::integral_constant<T, V>> :
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:15:28: error: incomplete type ‘Test<std::integral_constant<int, 0> >’
used in nested name specifier
 static_assert(std::is_same<Test<std::integral_constant<int, 0>>::type,
void>::value, "");
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:15:28: error: incomplete type ‘Test<std::integral_constant<int, 0> >’
used in nested name specifier
test.cpp:15:76: error: template argument 1 is invalid
 static_assert(std::is_same<Test<std::integral_constant<int, 0>>::type,
void>::value, "");