https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122621
Bug ID: 122621
Summary: [15/16 regression] ICE on CTAD for alias template with
contrained constructor
Product: gcc
Version: 15.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cmingyi01 at gmail dot com
Target Milestone: ---
The following C++20 code causes an ICE since GCC 15.
```
template <class, class>
concept constructible_from = true;
template <class... ElemTs>
struct Tuple {
template <class... Ts> requires (... && constructible_from<ElemTs, Ts>)
Tuple(Ts &&...) {}
};
template <class... ElemTs>
Tuple(ElemTs...) -> Tuple<ElemTs...>;
template <class... Ts>
using A = Tuple<Tuple<Ts...>>;
A f{Tuple{Tuple{0}}};
```
Output:
```
<source>: In substitution of 'template<class ... Ts, class ... Ts> requires
(... && constructible_from<ElemTs, Ts>) Tuple(Ts&& ...) -> Tuple<Tuple<ElemTs
...> > [with Ts = {}; Ts = {Tuple<int>}]':
required from here
<source>:16:20:
16 | A f{Tuple{Tuple{0}}};
| ^
required by the constraints of 'template<class ... Ts, class ... Ts> requires
(... && constructible_from<ElemTs, Ts>) Tuple(Ts&& ...) -> Tuple<Tuple<ElemTs
...> >'
<source>:7:5:
7 | Tuple(Ts &&...) {}
| ^~~~~
<source>:16:20: internal compiler error: in cxx_incomplete_type_diagnostic, at
cp/typeck2.cc:517
16 | A f{Tuple{Tuple{0}}};
| ^
0x2906548 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
???:0
0x28fb33b internal_error(char const*, ...)
???:0
0xb0ba68 fancy_abort(char const*, int, char const*)
???:0
0xe0ccd7 complete_type_or_maybe_complain(tree_node*, tree_node*, int)
???:0
0xb2eaab build_special_member_call(tree_node*, tree_node*, vec<tree_node*,
va_gc, vl_embed>**, tree_node*, int, int)
???:0
0xbc1933 force_rvalue(tree_node*, int)
???:0
0xb9dab8 constraints_satisfied_p(tree_node*, tree_node*)
???:0
0xda9c01 fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node*
const*, unsigned int, tree_node*, unification_kind_t, int, conversion**, bool,
bool)
???:0
0xb3e139 perform_dguide_overload_resolution(tree_node*, vec<tree_node*, va_gc,
vl_embed> const*, int)
???:0
0xd6d0b2 do_auto_deduction(tree_node*, tree_node*, tree_node*, int,
auto_deduction_context, tree_node*, int, tree_node*)
???:0
0xc0ff41 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int,
cp_decomp*)
???:0
0xd45523 c_parse_file()
???:0
0xeb5cc9 c_common_parse_file()
???:0
```
See https://compiler-explorer.com/z/h8jG8zqE9.
