https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78022
--- Comment #3 from fiesh at zefix dot tv ---
Interestingly, clang-5 no longer compiles this code:
<source>:28:15: error: constexpr variable 'b1' must be initialized by a
constant expression
constexpr B b1{0};
^~~~~
<source>:28:15: note: constructor inherited from base class 'A<int>' cannot be
used in a constant expression; derived class cannot be implicitly initialized
<source>:14:16: note: declared here
using A<int>::A;
^
1 error generated.
Compiler returned: 1
So gcc, clang <=4 and clang-5 behave pairwise differently. At most one of them
can be right, who might it be?
