[Bug c++/102116] New: structured binding is returned from a function as rvalue in C++20 mode

[Bug c++/102116] New: structured binding is returned from a function as rvalue in C++20 mode

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102116

            Bug ID: 102116
           Summary: structured binding is returned from a function as
                    rvalue in C++20 mode
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

In the following program:
```
#include <tuple>
#include <iostream>

struct A {
    A(const int &) { std::cout << "A(const int &) "; }
    A(int &&) { std::cout << "A(int &&) "; }
};

A foo() {
    auto [y] = std::make_tuple(1);
    return y;
}

int main() { foo(); }
```
GCC selects "A(int &&)" constructor starting from C++20 mode, demo:
https://gcc.godbolt.org/z/5q779vE6T

I asked why on stack-overflow:
https://stackoverflow.com/questions/68941451/shall-structured-binding-be-returned-from-a-function-as-rvalue-in-c20
and the answer was that GCC being wrong here.

Could you please confirm it or explain why the behavior of the program changes
in C++20 mode?

[Bug c++/102116] structured binding is returned from a function as rvalue in C++20 mode

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102116

--- Comment #1 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
Sorry, what do you mean by "wrong-code" tag? The code example is for sure
valid. It may be only unclear which one of two A-constructors must be called.

[Bug c++/102116] structured binding is returned from a function as rvalue in C++20 mode

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102116

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Fedor Chelnokov from comment #1)
> Sorry, what do you mean by "wrong-code" tag? The code example is for sure
> valid. It may be only unclear which one of two A-constructors must be called.

wrong-code keyword means GCC is out putting the wrong thing for the input of
valid code.  Does that make sense?

[Bug c++/102116] structured binding is returned from a function as rvalue in C++20 mode

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102116

--- Comment #3 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
Thanks a lot, it is clear now.

[Bug c++/102116] structured binding is returned from a function as rvalue in C++20 mode

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102116

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
If you follow the Keywords: hyperlink, you'll get description of all the
keywords...