[Bug c++/52036] C++11 allows template parameters to have internal linkage

[mimomorin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52036

Michel Morin <mimomorin at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mimomorin at gmail dot com

--- Comment #11 from Michel Morin <mimomorin at gmail dot com> ---
The internal linkage testcase

    template <typename T, const T &val> class TestClass {
        /* ... */
    };
    constexpr float pi = 3.14;
    int main()
    {
        TestClass<float, pi> test;
    }

compiles successfully from GCC 6.

However, Richard's testcase (i.e. testcase in the Standard)

    template<class T, const char* p> class X {
        /* ... */
    };
    const char p[] = "Vivisectionist";
    X<int,p> x;

fails to compile even on GCC 7 (in C++11/14 modes) with this error message

    error: the value of 'p' is not usable in a constant expression
     X<int,p> x;
           ^
    note: 'p' was not declared 'constexpr'
     const char p[] = "Vivisectionist";

As the message suggests, if `p` is declared as `constexpr` it compiles fine.
Note that in a C++1z mode (from GCC 5) it compiles fine without `constexpr`.