[Bug c++/48531] [C++0x][SFINAE] Hard errors with arrays of unknown bound

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48531

--- Comment #4 from Daniel Krügler <daniel.kruegler at googlemail dot com> 
2011-04-14 23:00:05 UTC ---
(In reply to comment #3)

Here is a minimalistic example that provokes the same error. The essence is,
that the construction expression is evaluated combined with another
construction or destruction expression in a single (constant) expression. The
other expressions seems not relevant, it can even be the same expression, like
here:

//-------------------
template<class T,
  class = decltype(T())
>
char f(int);

template<class>
double f(...);

struct B2 {
  B2(...);
};

constexpr bool b = sizeof(f<B2[1]>(0)) == 1 && sizeof(f<B2[1]>(0)) == 1;
//-------------------

"main.cpp:13:37: internal compiler error: in build_value_init_noctor, at
cp/init.c:455"

Another example case is, when we combine a destructor expression with a
constructor expression like this (Note that B1 is a slightly differently here):

template<class T,
  class = decltype(T())
>
char f(int);

template<class>
double f(...);

template<class T>
T&& create();

template<class T,
  class = decltype(create<T&>().~T())
>
char g(int);

template<class>
double g(...);

template<class... T>
struct B1 {
  B1(T...);
};

constexpr bool b = sizeof(g<B1<>[1]>(0)) == 1 && sizeof(f<B1<>[1]>(0)) == 1;


This gives exactly the same error:

"main.cpp:31:69: internal compiler error: in build_value_init_noctor, at
cp/init.c:455"

In addition to the ICE the new code gives incorrect results for an array with
known bounds of type with deleted d'tor. Given the same f as defined above
(testing for default construction):

struct D { ~D() = delete; };

static_assert(sizeof(f<D[1]>(0)) != 1, "Error");

the static assertion fires.