Fails to build with boost >= 1.87.0

[berolinux]

libzypp fails to build with boost 1.87.0 (1.86 is ok) because some pointer types sent to an iostream are now considered ambiguous.

[tomop-tg]

The same problem occurred in my environment.

• gcc 12.2
• boost 1.87.0

The error messages was as follows:

/home/myuser/rpm/BUILD/libzypp-17.35.15/zypp-core/base/PtrTypes.h:159:16: error: ambiguous overload for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'const boost::shared_ptr<void>')
  159 |   { return str << obj; }
      |            ~~~ ^~ ~~~
      |            |      |
      |            |      const boost::shared_ptr<void>
      |            std::ostream {aka std::basic_ostream<char>}
/home/myuser/rpm/BUILD/libzypp-17.35.15/zypp-core/base/PtrTypes.h:141:25: note: candidate: 'std::ostream& std::operator<<(ostream&, const boost::shared_ptr<X>&) [with D = void; ostream = basic_ostream<char>]'
  141 |   inline std::ostream & operator<<( std::ostream & str, const zypp::shared_ptr<void> & obj )
      |                         ^~~~~~~~
In file included from /usr/include/boost/shared_ptr.hpp:17,
                 from /home/myuser/rpm/BUILD/libzypp-17.35.15/zypp-core/base/PtrTypes.h:21:
/usr/include/boost/smart_ptr/shared_ptr.hpp:778:34: note: candidate: 'std::ostream& boost::operator<<(std::ostream&, const shared_ptr<X>&) [with Y = void; std::ostream = std::basic_ostream<char>]'
  778 | template<class Y> std::ostream & operator<< (std::ostream & os, shared_ptr<Y> const & p)
      |                                  ^~~~~~~~
gmake[2]: *** [zypp/CMakeFiles/zypp-objlib.dir/build.make:149: zypp/CMakeFiles/z
ypp-objlib.dir/pool/PoolStats.cc.o] Error 1

[berolinux]

The problem is that the std::ostream & operator << overloads in zypp-core/base/PtrTypes.h clash with the similar std::ostream & operator << overloads added in boost 1.87.0's boost/smart_ptr/shared_ptr.hpp

[berolinux]

Unless I'm overlooking something, there is no simple fix because boost's overloads and libzypp's are equally specialised, so there's no sane way to pick one over another -- so as a quick "fix", I've added a little patch to boost https://github.com/OpenMandrivaAssociation/boost/blob/master/boost-1.87.0-hack-for-libzypp-compatibility.patch and am building libzypp with -DBOOST_POINTERS_NO_IOSTREAM.
Not very nice, but effective (and since the iostream stuff is implemented inline in the headers, there won't be a symbol clash).

[gruenich]

Weird, the error message mentions two functions from libzypp and Boost. Both are more or less unchanged for more than a decade. There is no obvious recent change causing this problem.

[tomop-tg]

This problem seems to have been solved by boostorg/smart_ptr@e7433ba .