[Bug c++/104000] New: Ordinary constructor cannot delegate to `consteval` constructor

[Bug c++/104000] New: Ordinary constructor cannot delegate to `consteval` constructor

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104000

            Bug ID: 104000
           Summary: Ordinary constructor cannot delegate to `consteval`
                    constructor
           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: ---

This program
```
struct A {       
    int i = 0;
    consteval A() = default;
    A(int) : A() {}
};
```
is accepted by Clang so I assume it is valid. But GCC complains: error: 'this'
is not a constant expression

Demo: https://gcc.godbolt.org/z/3T9Pxdoz1

[Bug c++/104000] Ordinary constructor cannot delegate to `consteval` constructor

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104000

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The error is:
<source>: In constructor 'A::A(int)':
<source>:5:16: error: 'this' is not a constant expression
    5 |     A(int) : A() {}
      |                ^

[Bug c++/104000] Ordinary constructor cannot delegate to `consteval` constructor

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104000

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-01-21
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/104000] Ordinary constructor cannot delegate to `consteval` constructor

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104000

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|1                           |0
             Status|NEW                         |UNCONFIRMED

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Hmm, MSVC rejects it:
<source>(5): error C7595: 'A::A': call to immediate function is not a constant
expression

Are you sure this is not a bug in clang?

[Bug c++/104000] Ordinary constructor cannot delegate to `consteval` constructor

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104000

--- Comment #4 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
If we take MSVC into consideration, then it rejects
```
struct A {       
    consteval A() = default;
    A(int) : A() {}
};
```
which GCC accepts. So there is a divergence with MSVC as
well.https://gcc.godbolt.org/z/o8rqP14Gc

To be sure I asked the question: https://stackoverflow.com/q/70677825/7325599
Let us hope that it will be clarified.

[Bug c++/104000] Ordinary constructor cannot delegate to `consteval` constructor

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104000

--- Comment #5 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
Based on stackoverflow answer, a modified example was found with the delegation
to consteval constructor:
```
struct A {       
    int i = 0;
    consteval A() = default;
    A(const A&) = delete;
    A(int) : A(A()) {}
};
```
which is accepted in GCC. Demo: https://gcc.godbolt.org/z/5PjraK5ox

Clang rejects it until one remove `A(const A&) = delete`, which is probably
another issue.