[Bug c++/53878] New: Abstract class constructors

[Bug c++/53878] New: Abstract class constructors

[aschepler at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53878

             Bug #: 53878
           Summary: Abstract class constructors
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: aschepler@gmail.com


The following code is ill-formed C++03 and well-formed C++11, but g++ does not
accept it with the -std=c++0x flag:

class Base {
public:
  explicit Base(int);
};

class Abstract : virtual public Base {
public:
  Abstract();
  virtual ~Abstract() = 0;
};

Abstract::Abstract()
{}

See Standard 2011 section 12.6.2 paragraph 8.  "if a given non-static data
member or base class is not designated by a mem-initializer-id ... and the
entity is not a virtual base class of an abstract class, then ... [if the
entity is not a data member with an initializer in the class definition and is
not a variant member,] the entity is default-initialized". 

$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i486-linux-gnu/4.7/lto-wrapper
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.7.1-2'
--with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --enable-targets=all --with-arch-32=i586
--with-tune=generic --enable-checking=release --build=i486-linux-gnu
--host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.7.1 (Debian 4.7.1-2)

[Bug c++/53878] [C++11] Abstract class constructors

[aschepler at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53878

--- Comment #1 from Andrew Schepler <aschepler at gmail dot com> ---
Created attachment 36293
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36293&action=edit
Abstract class constructors may skip virtual bases

Attached is my attempt at a patch for this issue.  In addition to allowing an
abstract constructor to skip initializing virtual bases, this makes it so that
abstract classes have no "complete" constructors (which could never be called
anyway), only the "base" kind.

[Bug c++/53878] [C++11] Abstract class constructors

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53878

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |7.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed in GCC 7+.  I suspect by r7-3590 .

[Bug c++/53878] [C++11] Abstract class constructors

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53878

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Fixed in GCC 7+.  I suspect by r7-3590 .

pr66443-cxx14-3.C testcase looks like this case.