[Bug c++/67185] [C++14] Link error on ODR-use of variable template partial specialization

[Casey at Carter dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67185

Casey Carter <Casey at Carter dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Casey at Carter dot net
            Version|6.0                         |5.3.0
             Blocks|67491                       |
            Summary|[concepts] Link error on    |[C++14] Link error on
                   |ODR-use of constexpr        |ODR-use of variable
                   |constrained variable        |template partial
                   |template partial            |specialization
                   |specialization              |

--- Comment #1 from Casey Carter <Casey at Carter dot net> ---
This same bug is triggered by the purely C++14 program:

template <class>
bool x = false;

template <class T>
bool x<T*> = true;

bool& f() { return x<int*>; }

int main() {}

which when compiled with either g++ 5.3 or 6 results in 

/tmp/ccHHu1ip.o: In function `f()':
prog.cc:(.text+0x5): undefined reference to `x'
collect2: error: ld returned 1 exit status

The problem has nothing to do with concepts or constexpr, but seems to be a
general issue when ODR-using an instance of a template variable that was
instantiated from a partial specialization. I'm recasting this as a C++14 bug
against 5.3.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67491
[Bug 67491] [meta-bug] concepts issues