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

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

--
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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