https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105520
Bug ID: 105520
Summary: Ignores constraint in auto declaration with
braced-init-list
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cooky.ykooc922 at gmail dot com
Target Milestone: ---
>From the code snippet below:
#include <concepts>
#include <initializer_list>
template <typename T>
concept always_true = true;
template <typename T>
concept always_false = false;
template <typename>
inline constexpr bool is_init_list_v = false;
template <typename T>
inline constexpr bool is_init_list_v<std::initializer_list<T>> = true;
template <typename T>
concept not_init_list = !is_init_list_v<std::remove_cvref_t<T>>;
int main() {
always_true auto a = 10; // ok
always_true auto b = {1, 2, 3}; // ok
// always_false auto c = 10; // error as expected
// always_false auto d = {1, 2, 3}; // error as expected
not_init_list auto e = 10; // ok
not_init_list auto f = {1, 2, 3}; // no error but unexpected
// error as expected below:
// not_init_list auto g = std::initializer_list{1, 2, 3};
}
GCC accepts invalid code from `not_init_list auto f = {1, 2, 3}`, while Clang
rejects it as expected showing:
<source>:27:5: error: deduced type 'std::initializer_list<int>' does not
satisfy 'not_init_list'
not_init_list auto f = {1, 2, 3}; // no error but unexpected
^~~~~~~~~~~~~~~~~~
<source>:17:25: note: because
'!is_init_list_v<std::remove_cvref_t<initializer_list<int> > >' evaluated to
false
concept not_init_list = !is_init_list_v<std::remove_cvref_t<T>>;
^
compiler flag: -std=c++20
compiler explorer link: https://godbolt.org/z/G569rxb8f
