http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54541
Bug #: 54541
Summary: SFINAE bug: handling incomplete return types
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ts...@mail.ru
g++ 4.8.0 20120909 (experimental) fails to compile the following well-defined
code:
#include <utility>
struct X;
X f(int);
template <class T>
void g(decltype((void)f(std::declval<T>())) *)
{}
template <class T>
void g(...)
{}
int main()
{
g<int>(0);
}
COLLECT_GCC_OPTIONS='-v' '-std=c++11' '-shared-libgcc' '-mtune=generic'
'-march=pentiumpro'
test.cpp: In substitution of ‘template<class T> void g(decltype
((void)(f(declval<T>())))*) [with T = <missing>]’:
test.cpp:16:17: required from here
test.cpp:8:50: error: invalid use of incomplete type ‘struct X’
void g(decltype((void)f(std::declval<T>())) *)
^
test.cpp:3:12: error: forward declaration of ‘struct X’
struct X;
^
Compiler version info:
Target: i686-pc-linux-gnu
Configured with: ../configure --prefix=../target --enable-languages=c,c++
Thread model: posix
GNU C++ (GCC) version 4.8.0 20120909 (experimental) (i686-pc-linux-gnu)
compiled by GNU C version 4.8.0 20120909 (experimental), GMP version 5.0.2,
MPFR version 3.1.0, MPC version 0.8.2
Explanation:
When considering g<int>(0), for the former g the error [the expression
(void)f(std::declval<T>()) uses incomplete type X in a context where complete
type is required] occurs in immediate context (and there are no any errors in
non-immediate context), so the former g should be just excluded from the set of
candidate functions due to substitution failure. The latter g is the only
viable candidate, so it should be called.
