[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
                 CC|                            |mpolacek at gcc dot gnu.org

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |prokofjev.d at gmail dot com

--- Comment #13 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
*** Bug 90201 has been marked as a duplicate of this bug. ***

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

--- Comment #14 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I've encountered this bug with:

struct S { };
void g(S&&);

void
f (S&& arg)
{
  g(S(arg)); // warning: useless cast to type 'struct S'
}

which doesn't compile without the cast, because then "arg" is an lvalue that
cannot bind to S&&.

I'd like to disable then warning when a class is cast to a non-reference type.

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

--- Comment #15 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:b3c98d6a59a6dcd5b0b52bd5676b586ef4fe785f

commit r13-3388-gb3c98d6a59a6dcd5b0b52bd5676b586ef4fe785f
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Oct 18 12:20:14 2022 -0400

    c++: Mitigate -Wuseless-cast with classes [PR85043]

    -Wuseless-cast (not part of -Wall/-Wextra) warns here:

      struct S { };
      void g (S&&);
      void f (S&& arg)
      {
        g (S(arg)); // warning: useless cast to type 'struct S'
      }

    which is wrong: the code will not compile without the cast because
    "arg" is an lvalue which cannot bind to S&&.

    This patch disables the warning when an object that isn't a prvalue
    is cast to a non-reference type.  Therefore we still warn about the
    useless cast in "X(X{})".

            PR c++/85043

    gcc/cp/ChangeLog:

            * typeck.cc (maybe_warn_about_useless_cast): Don't warn when
            a glvalue is cast to a non-reference type.

    gcc/ChangeLog:

            * doc/invoke.texi: Update documentation of -Wuseless-cast.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wuseless-cast.C: Remove dg-warning.
            * g++.dg/warn/Wuseless-cast3.C: New test.

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #16 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Should be fixed now.

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0
                 CC|                            |ppalka at gcc dot gnu.org

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

--- Comment #17 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #16)
> Should be fixed now.

It seems the fix just silenced the -Wuseless-cast false positive without also
adding the separate -Wcast-to-the-same-type flag to cover that case instead; I
still think that would be useful.

[Bug c++/85043] -Wuseless-cast false positive for temporary objects; add separate -Wcast-to-the-same-type to cover that case instead

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

--- Comment #18 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The casts that are still warned about should really be useless so I don't plan
to add another warning.