[Bug c++/60399] constexpr ctor that does not init an attribute should be rejected but isn't

["daniel.kruegler at googlemail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60399

Daniel KrÃgler <daniel.kruegler at googlemail dot com> changed:

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--- Comment #1 from Daniel KrÃgler <daniel.kruegler at googlemail dot com> ---
No, the compiler is conforming: According to 7.1.6 p6:

"If the instantiated template specialization of a constexpr [..] member
function of a class template would fail to satisfy the requirements for a
constexpr function or constexpr constructor, that specialization is still a
constexpr function or constexpr constructor, even though a call to such a
function
cannot appear in a constant expression."

So, per se, the situation is well-defined here and there is fundamentally
nothing wrong with the constructor, because your code does not attempt to use
it in a constant expression. 

What makes your code ill-formed is the fact that your template could never be
instantiated to make the constructor a constexpr constructor, see the following
sentence:

"If no specialization of the template would satisfy the requirements for
a constexpr function or constexpr constructor when considered as a non-template
function or constructor, the template is ill-formed; no diagnostic required."

As you may notice, this kind of code does not require a diagnostics.