Public SourceMage Discussion List

[Robin Cook <rcook AT wyrms.net>]

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.

CuZnDragon
Robin Cook

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