[Bug c++/115196] New: Bad error message when using library functions from versions before they were introduced

[Bug c++/115196] New: Bad error message when using library functions from versions before they were introduced

[luigighiron at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115196

            Bug ID: 115196
           Summary: Bad error message when using library functions from
                    versions before they were introduced
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: luigighiron at gmail dot com
  Target Milestone: ---

GCC generates some error messages when attempting to use library functions
without including the appropriate header, indicating that the appropriate
header should be included. This seems to act incorrectly when attempting to use
a library function from a version before the function was introduced, for
example:

#include<memory>
int main(){
    std::to_address((void*)0);
}

std::to_address was introduced in C++20 so when using the default compilation
settings, i.e. C++17 this code is invalid. This is the generated error message
from testing on godbolt with GCC 14.1.0:

<source>: In function 'int main()':
<source>:3:10: error: 'to_address' is not a member of 'std'
    3 |     std::to_address((void*)0);
      |          ^~~~~~~~~~
<source>:2:1: note: 'std::to_address' is defined in header '<memory>'; this is
probably fixable by adding '#include <memory>'
    1 | #include<memory>
  +++ |+#include <memory>
    2 | int main(){

This note doesn't seem to be very helpful, it mentions adding an extra
'#include<memory>' when one is already present. A better error message here
would be to omit the note, or to make it mention changing the selected C++
standard version.

[Bug c++/115196] Bad error message when using library functions from versions before they were introduced

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115196

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Already fixed. Dup of bug 107800.

*** This bug has been marked as a duplicate of bug 107800 ***

[Bug c++/115196] Bad error message when using library functions from versions before they were introduced

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115196

--- Comment #2 from Sam James <sjames at gcc dot gnu.org> ---
See r14-10227-g5b96d547ce71b8.

[Bug c++/115196] Bad error message when using library functions from versions before they were introduced

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115196

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
You seem to imply it's a general problem, but I think it's specific to
sd::to_address, and that's already fixed.

[Bug c++/115196] Bad error message when using library functions from versions before they were introduced

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115196

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Halalaluyafail3 from comment #0)
> This note doesn't seem to be very helpful, it mentions adding an extra
> '#include<memory>' when one is already present. A better error message here
> would be to omit the note, or to make it mention changing the selected C++
> standard version.

If you'd tried gcc trunk on godbolt you'd have seen that's exactly what
happens:

<source>:3:10: note: 'std::to_address' is only available from C++20 onwards

There was just a typo which made gcc think std::to_address is part of <memory>
in C++11, so if it wasn't declared in your program then it must be because you
didn't include <memory>.

After the fix it correctly suggests using at least C++20.

[Bug c++/115196] Bad error message when using library functions from versions before they were introduced

[luigighiron at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115196

--- Comment #5 from Halalaluyafail3 <luigighiron at gmail dot com> ---
(In reply to Jonathan Wakely from comment #4)
> (In reply to Halalaluyafail3 from comment #0)
> > This note doesn't seem to be very helpful, it mentions adding an extra
> > '#include<memory>' when one is already present. A better error message here
> > would be to omit the note, or to make it mention changing the selected C++
> > standard version.
> 
> If you'd tried gcc trunk on godbolt you'd have seen that's exactly what
> happens:
> 
> <source>:3:10: note: 'std::to_address' is only available from C++20 onwards
> 
> There was just a typo which made gcc think std::to_address is part of
> <memory> in C++11, so if it wasn't declared in your program then it must be
> because you didn't include <memory>.
> 
> After the fix it correctly suggests using at least C++20.

My bad, I only tested this on GCC 14.1 and assumed that GCC 14.1 was recent
enough that it wouldn't have been changed.