[RFC] 1.7 Packaging: Obsolete packages

Brian Dessent brian@dessent.net
Fri Aug 22 01:30:00 GMT 2008

Corinna Vinschen wrote:

> IIUC, the ConnectedLoopFinder::visit() function is the core function
> which creates the dependency order.  What I don't get is this: The

That code is concerned with creating a topological ordering for the
specific purpose of running postinstall scripts.  This isn't called
until after the "remove old and unpack new" install phase is finished
and so the 'installed' member has already been set (e.g. the end of
Installer::installOne.)  Packages that are not selected or were earlier
uninstalled are irrelevant here; this is only about figuring out what
order to do postinstalls.

If you want to see a general example of dependency handling when a
package is selected, see ChooserPage::changeTrust (what is called when
you change everything at once, e.g. Curr to Exp) or
PickPackageLine::click (what is called when you click on a package.)  In
both cases the main workhorse is packagemeta::set_requirements and in
turn packageversion::set_requirements.  The logic for Replaces would
probably have to be wedged in there.

But it's a lot harder than just adding some code to deselect the
packages -- consider if setup followed the "Replaces:" advice and
unselected some packages because the user selected a new package, but
then they changed their mind and deselected that same package.  If we
don't go back and re-enable those packages then we potentially leave
them with a broken system.  We could delay this processing until later
in the process when the user no longer can change their mind, but then
the package selection pane becomes a lie.  We will potentially be
removing stuff that isn't marked as remove, and the "Selected" view no
longer accurately serves as a "here's a list of everything I'm about to
do" summary which I think is a valuable feature.


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