[Bug c++/106957] New: compiler error when calling lambda in decltype in trailing return type of function templated on T when passing T{} to the lambda

[Bug c++/106957] New: compiler error when calling lambda in decltype in trailing return type of function templated on T when passing T{} to the lambda

[enricomaria.dean6elis at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106957

            Bug ID: 106957
           Summary: compiler error when calling lambda in decltype in
                    trailing return type of function templated on T when
                    passing T{} to the lambda
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: enricomaria.dean6elis at gmail dot com
  Target Milestone: ---

Created attachment 53586
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53586&action=edit
the output/error upon compilation

Repro on godbolt (https://godbolt.org/z/9T5aEnzYa)

Question on stackoverlow with a comment sayint that the code would be illegal
anyway:
https://stackoverflow.com/questions/73747517/sfinae-ing-on-a-nullary-lambda-expression-calling-a-non-templated-function-on-a

Here's the code
```
#include <type_traits>

constexpr auto f = [](int){};

template<typename T>
auto canCallFOn(T) -> decltype([]{ f(T{}); }(), std::true_type{});

constexpr std::false_type canCallFOn(...) {
    return {};
}

int main() {
    static_assert(!canCallFOn(1));
    static_assert(!canCallFOn(""));
}
```

[Bug c++/106957] compiler error when calling lambda in decltype in trailing return type of function templated on T when passing T{} to the lambda

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106957

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-04-13
     Ever confirmed|0                           |1
           Keywords|rejects-valid               |error-recovery,
                   |                            |ice-on-invalid-code

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.