https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81339
Bug ID: 81339
Summary: no error for invalid decltype(T()) expression in
immediate context
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
struct true_type { static const bool value = true; };
struct false_type { static const bool value = false; };
template <typename T>
struct IsDefaultConstructibleT
{
// using T here (instead of U) should be an error
template <typename U, typename = decltype(T())>
static true_type test(void*);
template <typename U>
static false_type test(...);
static constexpr bool value = decltype(test<T>(nullptr))::value;
};
struct S {
S() = delete;
};
static_assert( IsDefaultConstructibleT<S>::value, "" ); // wrong
This should fail to compile, because T() is invalid, and is not a substitution
failure, but GCC compiles it, and even selects the true_type overload (so the
static assertion passes, which is doubly wrong).
Clang says:
n.cc:8:47: error: call to deleted constructor of 'S'
template <typename U, typename = decltype(T())>
^
n.cc:21:16: note: in instantiation of template class
'IsDefaultConstructibleT<S>' requested here
static_assert( IsDefaultConstructibleT<S>::value, "" );
^
n.cc:18:3: note: 'S' has been explicitly marked deleted here
S() = delete;
^
n.cc:21:1: error: static_assert failed ""
static_assert( IsDefaultConstructibleT<S>::value, "" );
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.
And EDG says:
"n.cc", line 8: error: the default constructor of "S" cannot be referenced --
it is a deleted function
template <typename U, typename = decltype(T())>
^
detected during instantiation of class "IsDefaultConstructibleT<T>
[with T=S]" at line 21
1 error detected in the compilation of "n.cc".
