[Bug c++/86728] [8/9 Regression] unexpected error: conversion from '<lambda(<type error>, ...)>' to non-scalar type 'std::function<void(int)>' requested

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86728

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

auto c = [](auto x ...) { };

86728.cc:1:23: error: parameter packs not expanded with ‘...’:
 auto c = [](auto x ...) { };
                       ^
86728.cc:1:23: note:         ‘auto:1’