Bug#954794: New packages must not declare themselves Essential

[Jonathan Nieder <jrnieder@gmail.com>]

Javier Serrano Polo wrote:
> On Wed, 30 Sep 2020 18:34:06 -0700 Jonathan Nieder <jrnieder@gmail.com>
> wrote:

>> Even so, some *rough* consensus on the plan is very useful for
>> helping people evaluate that first step.
>
> Here is a rough plan:
>
>    1. Policy: Packages should declare all their dependencies, even
>       essential ones.

I agree: this is the right first step.

More specifically, it's the right first three steps.

https://www.debian.org/doc/debian-policy/ch-binary.html#dependencies
currently says

	Packages are not required to declare any dependencies they
	have on other packages which are marked Essential (see below),
	and should not do so unless they depend on a particular
	version of that package.[4]

	[4] [...] If packages add unnecessary dependencies on packages
	in this set, the chances that there will be an unresolvable
	dependency loop caused by forcing these Essential packages to
	be configured first before they need to be is greatly
	increased.

I'd propose that as a first step we change that to

	Packages are not required to declare any dependencies they
	have on other packages which are marked Essential (see below),
	but are permitted to do so even if they do not depend on a
	particular version of that package.[4]

	[4] Functionality is rarely ever removed from the Essential
	set, but packages have been removed from the Essential set
	when the functionality moved to a different package. So when
	depending on these packages for such functionality, it is
	recommended to depend on an appropriate virtual package
	instead.

	Future versions of Debian policy may encourage and then
	require including explicit dependencies even for essential
	functionality. This is helpful to users putting together
	ultra-minimal systems (though Debian does not support omitting
	Essential functionality out of the box), and it means less
	work is required in case the moment comes to remove some
	functionality from the Essential set in the future.

(The next two steps would be to change that from "are permitted" to
"should", and then to "must".)

What do you think?

Thanks,
Jonathan

[4] "Essential is needed in part to avoid unresolvable dependency loops
on upgrade. If packages add unnecessary dependencies on packages in
this set, the chances that there will be an unresolvable dependency
loop caused by forcing these Essential packages to be configured first
before they need to be is greatly increased. It also increases the
chances that frontends will be unable to calculate an upgrade path,
even if one exists.

"Also, functionality is rarely ever removed from the Essential set, but
packages have been removed from the Essential set when the
functionality moved to a different package. So depending on these
packages just in case they stop being essential does way more harm
than good."