https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127276
Bug ID: 127276
Summary: P3598R0 testcase fails to compile
Product: gcc
Version: 16.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
The P3598R0 paper testcase clearly contains a lot of bugs, but if I try to fix
them all and remove the contracts, it is incorrectly rejected by g++ 16/trunk,
but works correctly with the clang++ reflection branch.
// { dg-do compile { target c++26 } }
// { dg-additional-options "-freflection" }
#include <array>
#include <map>
#include <meta>
#include <vector>
template <typename T1, typename T2>
auto
foo (const T1 &t1, const T2 &t2)
{
constexpr auto key = is_integral_type (^^T1) ? ^^t1 : ^^t2;
constexpr auto container = is_integral_type (^^T1) ? ^^t2 : ^^t1;
return [: container :][ [: key :] ];
}
void
bar (std::vector <int> &v)
{
foo (v, 5);
foo (5, v);
}
template <std::size_t N>
void
baz (std::array <int, N> &v)
{
foo (v, 5);
foo (5, v);
}
void
qux (std::map <int, int> &m)
{
foo (m, 5); // { dg-error "" }
foo (5, m); // { dg-error "" }
}
void
corge (std::array <int, 7> &v)
{
baz (v);
}
See https://godbolt.org/z/xzrzrfEfe ; the 2 calls in qux are correctly rejected
by clang++, no viable overloaded operator[] for type 'const std::map<int,
int>'
but g++ emits
error: subscripted value is neither array nor pointer
for all the calls, not just with map. Seems tsubst_expr on the ARRAY_REF with
SPLICE_EXPR as both operands results in build_x_array_ref on the REFERENCE_TYPE
PARM_DECLs directly rather than convert_from_reference of those, even when they
have reference type.
