[Bug c++/99505] New: ICE Segmentation fault when decltype lambda in parameter list

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99505

            Bug ID: 99505
           Summary: ICE Segmentation fault when decltype lambda in
                    parameter list
           Product: gcc
           Version: 9.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

This may be related/duplicated to the 99478, but I am not sure.

The following code will trigger ICE only on gcc-9:

int main() {
  [] (decltype([]{})) {} ({});
}

(godbolt: https://godbolt.org/z/xdr94q)

But this will trigger ICE on gcc-9, gcc-10 and gcc-11:

struct S {
  template <typename T>
  operator T() { return {}; }
};

int main() {
  [] (decltype([]{})) {} (S{});
}

(godbolt: https://godbolt.org/z/3dh477)