[Bug c++/101873] New: Compilation error of valid code with return local variable in C++20 mode

[Bug c++/101873] New: Compilation error of valid code with return local variable in C++20 mode

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101873

            Bug ID: 101873
           Summary: Compilation error of valid code with return local
                    variable in C++20 mode
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

The program as follows fails to compile in C++20 mode:
```
struct U {
    U(int) {}
    U(int&&) {}
};

U foo(int a = 0) { return a; }

int main() { foo(); }
```
But it is a valid program and other compilers accept it:
https://gcc.godbolt.org/z/fMvEPMGhq

[Bug c++/101873] Compilation error of valid code with return local variable in C++20 mode

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101873

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

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This is rejected since r11-2412-g1722e2013f05f1f1f99379dbaa0c0df356da731f
aka PR91427 fix.
Do the other compilers implement wg21.link/p1825 ?
Whether your testcase is valid or not I'll defer to others.

[Bug c++/101873] Compilation error of valid code with return local variable in C++20 mode

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101873

--- Comment #2 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
Thanks, I assumed that the code is valid based on stackoverflow answer:
https://stackoverflow.com/questions/68747489/is-the-local-variable-returned-by-a-function-automatically-moved-in-c20

[Bug c++/101873] Compilation error of valid code with return local variable in C++20 mode

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101873

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So questionable based on the status of https://wg21.link/p2266 and whether it
will be a DR or not?

[Bug c++/101873] Compilation error of valid code with return local variable in C++20 mode

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101873

--- Comment #4 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
If this question is to me, then actually I am not absolutely sure. I initially
thought that GCC was right in this code example. But later a high reputy C++
expert from stackoverflow dissuaded me. According to him, the code example was
valid in C++17 and remains valid in C++20. C++ standard is so complex nowdays.