[wpkg-users] [Bug 117] Dependencies ignore priority

[bugzilla-daemon at bugzilla.wpkg.org]

http://bugzilla.wpkg.org/show_bug.cgi?id=117





--- Comment #2 from Frank Lee <rl201 at cam.ac.uk>  2008-05-09 15:28:26 ---
> A dependency between packages means that a package REQUIRES that another
> package is installed - or it will fail to install/run. This means that if
> package A depends on package B then package B has to be installed BEFORE
> package A in any case. Regardless of the package priorities.

I disagree: dependencies are there so that one can request an installation of
package A which will also cause package B to be installed. It ought not to
imply that package B has to be installed before package A. The installation of
package B *before* package A (if required) is done by using priorities.

> Priorities are used only to sort the order of package installation. WPKG will
> install all packages in descending priority order. If a package (A) with very
> high priority depends on one with very low priority (B), then WPKG should still
> make sure that package A is installed with very high priority. Unfortunately
> the dependency then means that package B gets even higher priority in this case
> as it is required in order to be able to install package A.

Dependencies were introduced only so that we could nicely handle the case where
package A will not be useful unless package B is also installed. It made no
adjustments to the priority. WPKG should certainly install things in priority
order: what you seem to suggest is that it currently doesn't! (If package B is
a lower priority that package A, package A should be installed first, surely.
Not "installed first unless package A or a higher priority package depends on
it.")

> This is exactly the algorithm as WPKG uses it currently.
> Neither installing package A before package B nor the way to wait with package
> A until package B is installed (decreasing package A priority) is acceptable
> for me.
> So either I completely misunderstood you request (please clarify) or it is
> really breaking the idea of dependencies as I wrote.

The concepts of dependencies and priorities are orthogonal. A dependency means
that installing one package automatically pulls other packages into the list of
things to be installed. A priority gives WPKG a way of organising the list of
packages into some sensible order. By keeping the two concepts orthogonal, we
can adjust dependencies without changing the order of installation or we can
adjust priorities without changing which packages get installed.

If we make dependencies implicitly change the priority of sub-packages, we lose
that ability and things become much more confusing!

Yours,

Frank


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