[Bug c++/109385] New: decltype in lambda causes internal compiler error

[Bug c++/109385] New: decltype in lambda causes internal compiler error

[stevenxia990430 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109385

            Bug ID: 109385
           Summary: decltype in lambda causes internal compiler error
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stevenxia990430 at gmail dot com
  Target Milestone: ---

The following program reports an internal compiler error: Segmentation fault

To quickly reproduce: https://gcc.godbolt.org/z/WPWjs116W
```
#include <vector>
#include <algorithm>

int main() {
    auto sort_fn = [](auto... vals) {
        return [=]() {
            decltype(vals) vec;
        }();
    };

    auto result = sort_fn();
}
```

Removing the decltype(vals) inside the lambda removes the internal compiler
error. 

This crash seems to happen after and including gcc 8.1 to gcc 12.2

[Bug c++/109385] decltype in lambda causes internal compiler error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109385

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |c++-lambda,
                   |                            |ice-on-invalid-code

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is definitely invalid code as vals has variadic type. that is it needs to
be used inside a fold expressions or with ...

[Bug c++/109385] decltype in lambda causes internal compiler error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109385

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
clang rejects it with:
<source>:4:16: error: expression contains unexpanded parameter pack 'vals'
        return [=]() {
               ^
<source>:9:10: error: variable has incomplete type 'void'
    auto result = sort_fn();
         ^

[Bug c++/109385] decltype in lambda causes internal compiler error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109385

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-04-03
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=100035

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. Related to PR 100035.