https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70642
Bug ID: 70642
Summary: Invalid alias template instantiation not rejected if
previously used in SFINAE context
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rs2740 at gmail dot com
Target Milestone: ---
Reduced from http://stackoverflow.com/q/36578055/2756719.
The following ill-formed code is incorrectly accepted by GCC:
template<bool, class> struct enable_if {};
template<class T> struct enable_if<true, T> { using type = T; };
template <typename X>
struct foo
{
template <typename R>
using meow = typename enable_if<sizeof(X) == 0, R>::type;
template <typename R = int> // 1
meow<R> bar () = delete;
int bar ()
{
meow<int> i; // 2
return 0; // 3
}
};
int j = foo<long>().bar();
Attempting to use i (by changing line #3 to 'return i;') causes an ICE:
prog.cc: In instantiation of 'int foo<X>::bar() [with X = long int]':
prog.cc:20:25: required from here
prog.cc:16:16: internal compiler error: in tsubst_copy, at cp/pt.c:14043
return i;
^
0x6019dd tsubst_copy
/home/heads/gcc/gcc-source/gcc/cp/pt.c:14041
0x602021 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:16993
0x5fdcd8 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:15802
0x5fda06 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:15114
0x5fd454 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:15104
0x5fdb73 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:15290
0x5fc36f instantiate_decl(tree_node*, int, bool)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:22014
0x618c8b instantiate_pending_templates(int)
/home/heads/gcc/gcc-source/gcc/cp/pt.c:22131
0x636eed c_parse_final_cleanups()
/home/heads/gcc/gcc-source/gcc/cp/decl2.c:4599
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
The problem appears to only arise if the types in Lines #1 and #2 match (i.e.,
when the alias template has been instantiated in a SFINAE context already); if
either (but not both) is changed to, e.g., void, or if the first bar() overload
is removed, then the error is correctly diagnosed.
