Bug#819530: Bad interation with libstdc++ transition.

[nisse@lysator.liu.se (Niels Möller)]

Hi,

as a user, I experience a pretty bad interaction between this transition
and the recent libstdc++ transition.

I have a system with a mix of packages from stable and testing, which
usually works fine. However, upgrading to the latest libstdc++ at this
point breaks a lot of things due to gcc-6 C++ incompatibilities (which I
don't fully understand, I usually don't care much about C++). What I see
is that apt-get install -t testing libstdc++6 would have to uninstall
*lots* of stuff, including build-essential, texlive, libreoffice and
most of kde. So I don't want to do that at this time.

Directly broken packages on my system are

$ aptitude search -F '%c %p %V' '?and(?installed,?reverse-breaks(?and(?name("libstdc\\+\\+6$"),?version("6\\.2\\..*"))))'
i libboost-date-time1.55.0 1.55.0+dfsg-3 
i libkolabxml1             1.0.2-2       
i libreoffice-core         1:4.3.3-2+deb8
i libstdc++6               4.9.2-10      
i libstdc++6:i386            

This is the background, and now I would like to upgrade to libicu57,
because that blocks upgrade of wget, making it a "kept back" packet.
Dependency chain: wget-1.18 -> libpsl5 -> libicu57.

Now the interesting part: libicu57 has a dependency on libstdc++6 (>=
5.2). So it doesn't need gcc-6, gcc-5 is good enough. But the
libstdc++6 packages for gcc-5 are no longer in the archive, the only
versions available as far as I can find are 4.9.2-10 (which I have
installed), and 6.2.0-6, and the latter one breaks half of the world, as
described above. And then non-existence of version 5.x (x >= 2) of
libstdc++6 makes the libicu upgrade depend on upgrading libstdc++6 to
gcc-6, even though it shouldn' have to.

I've looked at the mirror I use, I'd expect libstdc++6 version 5.x to be
located in main/g/gcc-5/, but it's not there. I don't really understand
the process, but I guess the packages were deleted when gcc-6 migrating
to testing?

I don't know what to do about it, maybe it is an issue for the release
team, but I though I should raise the problem here first. To untangle
the transitions, one would need an libicu57 with a libstdc++6 dependency
which can be satisfied by some package which (i) is older than gcc-6 and
(ii) is actually installable from the package archive. Options I see
(not sure what's possible):

* Recompile libicu57 with gcc-4. 

* Resurrect gcc-5 libstdc++6 library packages in the archive.

Regards,
/Niels

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