https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120686
Bug ID: 120686
Summary: ICE on a lambda that uses parameter pack capture and
parameter pack indexing in decltype return type
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: e.siga at proton dot me
Target Milestone: ---
template<int I>
struct constant {};
template<typename ...Args>
auto fast_tuple(Args... args)
{
return
[...args = args]
<int I>
(constant<I>)
-> decltype(args...[I])
{
return args...[I];
};
}
int main()
{
auto r = fast_tuple(1, 2.0);
auto &&ll = r(constant<0>{});
}
==================================================
https://godbolt.org/z/Y44sT6qdr
Unfortunately I couldn't minimize this code snippet more:
* If you change the return type of the lambda (-> decltype(args...[I])), it
stops crashing
* If you remove constant<I> and start using non-deduced index, it stops
crashing
Somehow the synergy of these features causes the crash
