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["Andraž 'ruskie' Levstik" <ruskie AT codemages.net>]

On 03:27:31 2008-08-26 Robin Cook <rcook AT wyrms.net> wrote:
> On Mon, 2008-08-25 at 17:36 +0200, "Andraž 'ruskie' Levstik" wrote:
> > On 17:07:48 2008-08-25 Fredrik Carlström
> > <fredrik.carlstrom AT tele2.se> wrote:
> > > Hi
> > >  
> > > I've noticed some problems with circular dependencies between
> > > spells in sorcery. For example casting pkgconfig and enabling the
> > > optional dependency on glib2, will fail if pkgconfig isn't already
> > > installed. This is because pkgconfig is a build time requirement
> > > for glib2, but sorcery will try to install glib2 before pkgconfig.
> > > Is this a bug, or isn't resolution of circular dependencies
> > > implemented in sorcery?
> > >  
> > > If the latter is the case, this is a sketch of a simple and perhaps
> > >  possible solution. Observe that I'm not familiar with how this is  
> > > currently done in sorcery, so this might be easy, hard or even  
> > > impossible to implement. There might be problems and that I'm not
> > > aware of. Perhaps someone more familiar with sorcery than I, could
> > > take a look at this and see if it's at all possible to do.
> > >  
> > > First, unconditional circular dependencies between packages (as for
> > >  example between tetex and tetex-texmf) would have to be resolved.
> > >  The
> > > only way this can happen (outside the tool chain) is if at least
> > > one is a runtime dependency of the other. These must be labeled as
> > > such. To get this solution to work, it is only needed in those rare
> > > cases where there are an explicit unconditional circular dependence
> > > between packages.
> > >  
> > > We get:
> > > runtime_depends    Must be installed before or after this package.
> > > depends            Must be installed before this package is built.
> > > optional_depends   Must be installed before configuring and
> > > building with this support.
> > >  
> > > While collecting spells for installation, runtime dependencies can
> > > be treated as before. There will be no essential difference in the  
> > > collection of spells to cast. While casting spells, runtime
> > > dependencies can be ignored.
> > >  
> > > The part that must be reimplemented is the casting of queued
> > > spells. This can be done in two functions:
> > >  
> > > The first function will loop through the queue repeatedly and
> > > install spells that have all build time dependencies fulfilled,
> > > until the queue is empty.
> > >  
> > > function install(queue) {
> > >  while the install queue is nonempty {
> > >    for pkg in queue {
> > >      if all build time dependencies are fulfilled
> > >        cast pkg # and remove from the queue
> > >        dequeued=true
> > >      }
> > >    if not dequeued then forced_install(queue) # If there is a
> > >    circular
> > > blocking optional dependency
> > >  }
> > > }
> > >  
> > > The second function forces an installation if there is a circular  
> > > blocking optional dependency
> > >  
> > > function forced_install(queue) {
> > >  search the queue after a package pkg with all unconditional  
> > > dependencies fulfilled,
> > >                            and as few optional dependencies as
> > >                            possible
> > > that are not installed
> > >  cast pkg # without the optional_depends from spells that are not  
> > > currently installed, but do NOT remove from the queue
> > > }
> > >  
> > > Somewhere in this, self triggers and logging etc must be checked
> > > and done as well. This is so that all the intricate internals of
> > > spell casting are fulfilled.
> > >  
> > > If this could be implemented, the example with pkgconfig and glib2
> > > would be solved as follows:
> > > First install(queue) will try to install glib2 and pkgconfig, but
> > > fail miserably with both due to a circular dependency. Then
> > > forced_install will cast pkgconfig without the optional support for
> > > glib2. After that glib2 can be casted, and at last pkgconfig will
> > > be reinstalled with support for glib2.
> > >  
> >  
> > This can easily be bypassed in the spells themselves...
> >  
> > if spell_installed glib2 ; then optional_depends glib2
> > fi
> >  
> 
> But it still doesn't solve the issue where the user wants the pkgconfig
> to use glib2 so it needs the second cast to build it against the glib2.
> 
> There are a lot of these I hit recently as well in reinstalling a
> system.   Like spells that cups depends on but they themselves have
> optional depends on cups.
> 

Sure it does... it will not break out of the box. Also what kind of benefit
does one get from glib2 support in pkgconfig... I mean after all all it
does is read /usr/lib/pkgconfig files iirc

--
Andraž "ruskie" Levstik
Source Mage GNU/Linux Games grimoire guru
Geek/Hacker/Tinker

Be sure brain is in gear before engaging mouth.
Quis custodiet ipsos custodies.
Ryle hira.

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