[Bug c++/13481] New: No destuctor assumed in a forward declared class when being used in template

[ikm at pisem dot net]

When trying to call the implied destructor in a forward declared class within a
template class, g++ 3.3 asserts this as an invalid usage of a forward
declaration. Everything was ok in g++ 3.2 and the code worked fine.

The following code shows the problem. It compiles and works fine on gcc 3.2, but
fails on gcc 3.3.

#include <iostream>

// Forward declaration
class Forward;

// Some template using T's destructor explicitly
template< class T >
class Template
{
  T * object;

public:

  Template() {}

  Template( T * object_ ): object( object_ )
  {}

  
  void destruct()
  {
    // g++ 3.2 knew that Forward has a destructor at this point, but g++ 3.3
    // does not think so these days.
    object->~T();
  }
};


// This class attempts using the template
class User
{
public:
  Template< Forward > t;

  User( Forward * f): t( f ) {}

  void use()
  { t.destruct(); }
};

// Here actually comes the body of Forward
class Forward
{
public:

  ~Forward()
  {
    std::cerr << "Destructing Forward" << std::endl;
  }
};



int main()
{
  Forward * f = new Forward;

  User user( f );

  user.use();

  return 0;
}

////////////////////////////////

With g++-3.2 -Wall, everything compiles fine without any warning and actually
works, outputting the "Destructing Forward" message as expected. g++-3.3 shows
the following:

$ g++-3.3 -v -Wall test.cc

Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.3/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib
--enable-nls --without-included-gettext --enable-__cxa_atexit
--enable-clocale=gnu --enable-debug --enable-java-gc=boehm
--enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.3 20031206 (prerelease) (Debian)
 /usr/lib/gcc-lib/i486-linux/3.3.3/cc1plus -quiet -v -D__GNUC__=3
-D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=3 -D_GNU_SOURCE test.cc -D__GNUG__=3
-quiet -dumpbase test.cc -auxbase test -Wall -version -o /tmp/ccnjudqp.s
GNU C++ version 3.3.3 20031206 (prerelease) (Debian) (i486-linux)
        compiled by GNU C version 3.3.3 20031206 (prerelease) (Debian).
GGC heuristics: --param ggc-min-expand=47 --param ggc-min-heapsize=32058
ignoring nonexistent directory "/usr/i486-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/3.3
 /usr/include/c++/3.3/i486-linux
 /usr/include/c++/3.3/backward
 /usr/local/include
 /usr/lib/gcc-lib/i486-linux/3.3.3/include
 /usr/include
End of search list.
test.cc: In member function `void Template<T>::destruct() [with T = Forward]':
test.cc:38:   instantiated from here
test.cc:24: error: invalid use of undefined type `struct Forward'
test.cc:4: error: forward declaration of `struct Forward'


I actually miss that functionality that allowed me to create nice smart pointers
in the past.

-- 
           Summary: No destuctor assumed in a forward declared class when
                    being used in template
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ikm at pisem dot net
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13481