On Wed, 2005-07-27 at 11:22 -0600, Bruce Sass wrote: > On Wed, 27 Jul 2005, Frank Küster wrote: > > Nicolas Boullis <nboullis@debian.org> wrote: > > > > > Oh, and I just thought there could be a workaround. I could make a new > > > no-udev empty package that conflicts with udev, and then write > > > "Recommends: no-udev | udev (>= 0.060-1)". > > > > An elegant solution ;-) > > > > > I guess this would behave as expected, but I think that having one more > > > package only for this would be quite insane! > > > > Especially because others would pick up the idea... > > Can dpkg/apt/etc. be tweaked to automatically Provides: no-* ? Two methods, one is not tenable: (a) X conflicts with no-X implicitly (b) When Y depends on no-X, if Y is installed, no-X is synthesised and installed too if it doesn't exist, (and conflicting with X to prevent X being installed). The dummy installation is mandatory because here is the alternative, which is not tenable: When installing X, scan all installed packages to see if there is a dependency on no-X, if so there is a conflict. This is untenable because it requires scanning all packages in your local database, whereas installation of a package should only require looking up the listed dependencies. The reason a logical 'X isn't installed' does not work is that you could install Y, which depends on no X, and then just install X. Now Y is silently broken by a package that knows nothing about Y. The first technique works 'as if for each package X, either X or no-X was installed' and is the same as for the manual installation of a no-X package except it is handled by apt automatically and doesn't require any no-X package in the repository (but one must still be physically entered into your local database). The proof is by Shroedingers Cat: either X or no-X is always physically installed whenever you require a dependency, it is irrelevant whether or not X or no-X is installed otherwise, so the absence of one or the other is also irrelevant. -- John Skaller <skaller at users dot sourceforge dot net>
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