[Bug c++/67240] New: [concepts] Implicit conversion constraints are not respected

[sebi707 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67240

            Bug ID: 67240
           Summary: [concepts] Implicit conversion constraints are not
                    respected
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sebi707 at gmail dot com
  Target Milestone: ---

Using the trailing return type to add constraints does not work in some cases.
The following code should not compile:

int foo(int x)
{
    return x;
}

template <typename T>
concept bool C1 = requires (T x) {
    {foo(x)} -> int&;
};

template <typename T>
concept bool C2 = requires (T x) {
    {foo(x)} -> void;
};

static_assert( C1<int> );
static_assert( C2<int> );

However this compiles just fine with r226884.