[Bug c++/115580] New: decltype of nullptr error with -Werror=nonnull

[Bug c++/115580] New: decltype of nullptr error with -Werror=nonnull

[marcpawl at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115580

            Bug ID: 115580
           Summary: decltype of nullptr error with -Werror=nonnull
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marcpawl at gmail dot com
  Target Milestone: ---

-Werror=nonnull returns error when using nullptr to get type of member
function.

Even though we are using -Werror=nonnull, there should be no diagnostic
since the function is never evaluated, and it is non-virtual.


https://godbolt.org/z/3oh1199Wh
https://stackoverflow.com/questions/5580253/how-do-i-get-the-return-type-of-a-member-function-without-an-object


class WithMember {
public:
  int foo();
};

decltype(((WithMember*)nullptr)->foo()) footype;

<source>:7:37: error: 'this' pointer is null [-Werror=nonnull]
    7 | decltype(((WithMember*)nullptr)->foo()) footype;
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
<source>:4:7: note: in a call to non-static member function 'int
WithMember::foo()'
    4 |   int foo();
      |       ^~~
<source>:7:37: error: 'this' pointer is null [-Werror=nonnull]
    7 | decltype(((WithMember*)nullptr)->foo()) footype;
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
<source>:4:7: note: in a call to non-static member function 'int
WithMember::foo()'
    4 |   int foo();
      |       ^~~
cc1plus: some warnings being treated as errors
Compiler returned: 1

[Bug c++/115580] [11/12/13/14/15 regression] decltype of nullptr error with -Werror=nonnull

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115580

Sam James <sjames at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|decltype of nullptr error   |[11/12/13/14/15 regression]
                   |with -Werror=nonnull        |decltype of nullptr error
                   |                            |with -Werror=nonnull

--- Comment #1 from Sam James <sjames at gcc dot gnu.org> ---
10 works.

[Bug c++/115580] [11/12/13/14/15 regression] null pointer warning from an unevaluated context

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115580

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-06-21
             Status|UNCONFIRMED                 |NEW
   Target Milestone|---                         |11.5
            Summary|[11/12/13/14/15 regression] |[11/12/13/14/15 regression]
                   |decltype of nullptr error   |null pointer warning from
                   |with -Werror=nonnull        |an unevaluated context
     Ever confirmed|0                           |1
      Known to fail|                            |11.1.0
      Known to work|                            |10.1.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The this pointer case was introduced by r11-6900-gd6f1cf644c45b7 (and )

BUT this has always been an issue:
```
int f(void*) __attribute__((nonnull));

void g()
{
        decltype(f(nullptr)) b;
}
```

This should not warn since we are inside an unevaluated context.