[Pkg-zsh-devel] Bug#707760: zsh: Alternatives broken for long time during upgrade from zsh4 to zsh5

[Aaron Schrab]

At 11:23 +0200 11 May 2013, Axel Beckert <abe at debian.org> wrote:
>Not nice, indeed. I though have no immediate idea what could have
>caused this. I though think that this issue, if not caused by other
>issues, is quite important to fix.

As far as I can tell, it's just caused by how dpkg works.

As it's supposed to do, dpkg first unpacked the new version of zsh and 
removed the old version along with doing the same for the other packages 
being upgraded in that run.  Only once that was done did it start 
running the postinst scripts for the packages one by one.

In most cases this isn't much of an issue, most packages will work at 
least somewhat when not configured or when the configuration step was 
done for a previous version of the package.  Here since the actual 
executable moved from /bin/zsh4 to /bin/zsh5 during the unpacking phase 
but update-alternatives wasn't called to do its work until the postinst 
script was run this left the /bin/zsh and /usr/bin/zsh links broken 
during that time.  Once the postinst script actually ran, the problem 
was resolved.

This would likely be difficult to notice during development.  Since in 
that case it's likely that the zsh package would be upgraded by itself 
rather than with a large number of other packages, in which case there 
wouldn't be much of a gap between when the package is unpacked and when 
the postinst script is run.