[Bug c++/115557] New: initializing reference property inside template context - error is not recognized

[Bug c++/115557] New: initializing reference property inside template context - error is not recognized

[nmmm at nmmm dot nu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115557

            Bug ID: 115557
           Summary: initializing reference property inside template
                    context - error is not recognized
           Product: gcc
           Version: 14.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nmmm at nmmm dot nu
  Target Milestone: ---

Following code compiles without error or warning.

B::A &a{ 4 }; - this should emit error.

clang catch this and error message is:
non-const lvalue reference to type 'A' cannot bind to an initializer list
temporary



struct A{
    A(int){}
};

template<typename T>
struct B{
    B(A &a) : a(a){}

    A &a{ 4 }; // this is wrong
};

int main(){
    A a{ 5 };

    B<double> b(a);
}

[Bug c++/115557] Invalid NSDMI accepted for templates classes for a aggregate that binds to a temp

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115557

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|initializing reference      |Invalid NSDMI accepted for
                   |property inside template    |templates classes for a
                   |context - error is not      |aggregate that binds to a
                   |recognized                  |temp
      Known to fail|                            |4.7.1
             Status|UNCONFIRMED                 |NEW
             Blocks|                            |58616
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-06-21

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
A does not need to have a ctor either.
This is also invalid:
```
struct A{ int t; };

template<typename T>
struct B{
    B(A &a) : a(a){}

    A &a{ 4 }; // this is wrong
};

int main(){
    A a{5};

    B<double> b(a);
}
```

GCC has incorrectly accepted this since NSDMI support was added in 4.7.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58616
[Bug 58616] [meta-bug] nsdmi

[Bug c++/115557] Invalid NSDMI accepted for templates classes for a aggregate that binds to a temp

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115557

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
We catch that problem if the initializer is actually used:

```
struct A{ int t; };

template<typename T>
struct B{
  A &a{ 4 }; // this is wrong
};

int main(){
    B<double> b2{};
}
```

115557-2.C:5:6: error: cannot bind non-const lvalue reference of type ‘A&’ to
an rvalue of type ‘A’
    5 |   A &a{ 4 }; // this is wrong