KDE3 apps running in a KDE4-modified environment

[Andreas Pakulat]

On 18.04.07 16:07:36, Thiago Macieira wrote:
> Rex Dieter said:
> > Thiago Macieira wrote:
> >> Mauricio Piacentini wrote:
> >>> But the potential problem exists now: what if an user
> >>> installs KDE4, runs Kmahjongg 4, and then attempts to install, download
> >>> and run the KDE3 version?
> >>
> >> You're not allowed to do that. KDE applications do NOT support
> >> downgrading.
> >>
> >> They never have.
> >
> > Wouldn't such a policy prevent kde3/kde4 ever being able to be installed
> > into the same prefix?  Or am I missing something?
> 
> That depends.
> 
> You are in no way allowed to downgrade applications once their config
> files have been touched. That's valid for a 3.5 to 4.0 upgrade as well as
> 3.4 to 3.5 or 4.0 to 4.1. Especially if there's an .upd script.
> 
> However, there are some shared config files (like kdeglobals) that we have
> to check for backwards compatibility before the 4.0 release. Those files
> should never be the target of an .upd script.
> 
> We don't have it yet, but we could have a KDE4HOME variable that overrides
> KDEHOME for KDE 4 applications. That way, you'll have two separate config
> directories for your 3 and 4 applications. However, this could hinder the
> upgrade, because applications will not notice the old config file (maybe
> we could treat KDEHOME in the presence of KDE4HOME as just one more
> KDEDIRS...)

But KDEHOME is not about the prefix. In the last days and weeks there
was some effort to make sure kde4 and kde3 can live in the same prefix.
But how does this work if application A/kde4 installs a new config file
in the data dir which A/kde3 doesn't understand? Are there going to be
different data dirs for kde4 (like share/kde4/apps/<appname> or
share/apps/kde4/<appname>)?

Andreas

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