[llvm-bugs] [Bug 37450] New: clang falsely(?) accepts c++17 code in c++14 mode?

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37450

            Bug ID: 37450
           Summary: clang falsely(?) accepts c++17 code in c++14 mode?
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: lebedev.ri at gmail.com
                CC: llvm-bugs at lists.llvm.org

This is creduce output, and it's not really easy to follow i'm afraid :/

https://godbolt.org/g/VMF1Ww

template <template <typename> class a> struct c {
  template <typename> struct B { typedef a<int> d; };
};
template <template <typename> class e> struct f { typedef c<e> b; };
template <template <typename> class e> struct g { typedef f<e> d; };
template <class h> struct i {
  static int j() {
    typedef typename h::template B<int>::d k;
    new k;
    return 0;
  }
};
template <typename l> struct m {
  int j() {
    (void)i<typename l::b>::j;
    return 0;
  }
};
template <typename> struct n {
  static constexpr auto o = [] {};
};
bool p = &m<g<n>::d>::j;


Clang trunk accepts this without any warning with  -Wall -Wextra -Werror
-std=c++14
gcc 8.1, with the same options, fails with 

<source>: In instantiation of 'constexpr const n<int>::<lambda()> n<int>::o':
<source>:20:25:   required from 'struct n<int>'
<source>:9:5:   required from 'static int i<h>::j() [with h = c<n>]'
<source>:15:5:   required from 'int m<l>::j() [with l = f<n>]'
<source>:22:23:   required from here
<source>:20:25: error: the type 'const n<int>::<lambda()>' of 'constexpr'
variable 'n<int>::o' is not literal
   static constexpr auto o = [] {};
                         ^
<source>:20:25: note: 'n<int>::<lambda()>' is not literal because:
cc1plus: note:   'n<int>::<lambda()>' is a closure type, which is only literal
in C++17 and later
<source>:20:25: error: in-class initialization of static data member 'const
n<int>::<lambda()> n<int>::o' of non-literal type

Compiler returned: 1



Is this clang's or gcc's bug?

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