The following code refuses to compile :
----------------------------
struct C;
template < typename T >
struct B;
template < typename T >
struct A;
void f(const C &c); // this one is fine
void f(const B<C> &a); // this one is fine
void f(const A<C> &a); // this one triggers the bug
void f(double) {}
template < typename T >
struct A
{
B<T> b;
};
int main()
{
f(1.0); // => instantiates A<C> => instantiates B<C> => fails.
}
-------------------------------
The error message is :
instance.C: In instantiation of 'A<C>':
instance.C:23: instantiated from here
instance.C:17: error: 'A<T>::b' has incomplete type
instance.C:4: error: declaration of 'struct B<C>'
I am not 100% sure it is a SFINAE bug, but it looks like one to me.
Note that if you comment the declaration of f(A<C>), then it works.
Similarly if you comment the definition of A.
So the problem here is probably that if the definition of A is
available, then the compiler instantiates it, which triggers the
instantiation of B<T>, which fails, but the compiler does not
recover from this instantiation as it should (following SFINAE).
There is the same problem with g++ 3.3, 3.4 and 4.0.1.
--
Summary: SFINAE bug
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sylvain dot pion at sophia dot inria dot fr
CC: gcc-bugs at gcc dot gnu dot org,sylvain dot pion at
sophia dot inria dot fr
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23227
