[Bug c++/58114] New: allow turning the warning about deleting a pointer of incomplete type into an error

[Bug c++/58114] New: allow turning the warning about deleting a pointer of incomplete type into an error

[tilman.vogel at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58114

            Bug ID: 58114
           Summary: allow turning the warning about deleting a pointer of
                    incomplete type into an error
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tilman.vogel at web dot de

While many warning messages have a way to control their emission and treatment,
e.g. "warning: multi-line comment [-Wcomment]", some warnings do not, in
particular:

warning: possible problem detected in invocation of delete operator: [enabled
by default]
warning: 'value' has incomplete type [enabled by default]

As a consequence of being enabled by default, there does not seem to be an
associated warning class that I could pass to "-Werror=". 

I'd really like to be able to say 
"-Werror=delete-with-incomplete-type"

[Bug c++/58114] allow turning the warning about deleting a pointer of incomplete type into an error

[fuscated at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58114

Teodor Petrov <fuscated at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fuscated at gmail dot com

--- Comment #1 from Teodor Petrov <fuscated at gmail dot com> ---
This option is very important, because this warning allowed us to fix one
serious leak in our application. And to prevent this problem to reappear in the
future we want to force this warning to be error, but unfortunately we are not
able when building with GCC.

All other compilers we use have this feature. And btw in clang the option is
named -Wdelete-incomplete, so you can reuse it to minimize the difference
between the compilers.

BTW: Do someone has an explanation why this is allowed in the standard?

[Bug c++/58114] allow turning the warning about deleting a pointer of incomplete type into an error

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58114

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-04-16
     Ever confirmed|0                           |1
           Severity|enhancement                 |normal

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Teodor Petrov from comment #1)
> BTW: Do someone has an explanation why this is allowed in the standard?

Because it's only a problem if the type has a non-trivial destructor or an
overloaded operator delete. For a type with a trivial destructor (such as a
POD) all that needs to be done is deallocate the memory.

The standard says:

"If the object being deleted has incomplete class type at the point of deletion
and the complete class has a non-trivial destructor or a deallocation function,
the behavior is undefined."

Since the compiler can't know if an incomplete type has a trivial destructor or
not, it can only warn, not give a hard error. If you want to make it a hard
error in your own program you should be able to, so confirming.

[Bug c++/58114] allow turning the warning about deleting a pointer of incomplete type into an error

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58114

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE
   Target Milestone|---                         |4.9.0

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Actually it looks as though -Wdelete-incomplete is already supported

*** This bug has been marked as a duplicate of bug 43452 ***

[Bug c++/58114] allow turning the warning about deleting a pointer of incomplete type into an error

[fuscated at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58114

--- Comment #4 from Teodor Petrov <fuscated at gmail dot com> ---
@Jonathan Wakely: Do you think the ISO C++ standard people will be willing to
change this behaviour for a future standard? I'm asking in order to know if
there is any point in starting a conversation with them.

[Bug c++/58114] allow turning the warning about deleting a pointer of incomplete type into an error

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58114

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
That change would force compilers to reject currently valid programs that have
well-defined behaviour. Changes that like are not popular.

It is valid in C to pass a pointer to an incomplete type to free(), and this
C++ rule is compatible. You can delete incomplete types if they have trivial
destructors (like C structs).