[Python-Dev] Keyword meanings [was: Accept just PEP-0426]
pje at telecommunity.com
Sat Dec 8 21:18:15 CET 2012
On Sat, Dec 8, 2012 at 5:06 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On Sat, Dec 8, 2012 at 4:46 PM, PJ Eby <pje at telecommunity.com> wrote:
>> So if package A includes a "Conflicts: B" declaration, I recommend the
>> * An attempt to install A with B already present refuses to install A
>> without a warning and confirmation
>> * An attempt to install B informs the user of the conflict, and
>> optionally offers to uninstall A
>> In this way, any collateral damage to B is avoided, while still making
>> the intended "lack of support" declaration clear.
>> How does that sound?
> No, that's not the way it works. A conflict is always symmetric, no matter
> who declares it.
But that *precisely contradicts* what you said in your previous email:
> It's to allow a project to say
> *they don't support* installing in parallel with another package.
Just because A doesn't support being installed next to B, doesn't mean
B doesn't support being installed next to A. B might work just fine
with A installed, and even be explicitly supported by the author of B.
Why should the author of A get to decide what happens to B? Just
because I trust A about A, doesn't mean I should have to trust them
Look, I really don't care about the individual fields' definitions
that much. I care about only one thing: A shouldn't get to (de facto)
dictate what happens to B. If you *really* want the behavior to be
symmetrical, then it should *only* be symmetrical if both A and B
*agree* they are in conflict. (i.e., both refer to the other in their
conflict fields). Otherwise, it should only be a warning.
There are tons of other things that I could argue here about the
positions you've laid out. But all I *really* care about is that we
not define fields in such a way as to permit or encourage
inter-package warfare -- intentional or not. Solutions acceptable to
me include (in no particular order):
* Make declarations affect only the declarer (as with Obsoleted-By)
* Make declarations only warn users, not block installation or result
* Have no automated action at all, and document them as intended for
downstream repackagers only
* Toss the field entirely
* Make the field include a context (e.g. a distro name), so that only
tools explicitly told you're operating in that context pay attention
* Use the new metadata extension vocabularies to define hints for
specific downstream packaging tools and systems
* Replace "conflicts" with a specification of resources actually used
by the project, so that such conflicts can be automatically detected
without needing to target a specific project
And there are probably others I haven't thought of yet. If you can be
clearer about what it is you want from the Conflicts field *other*
than just wanting it to stay as is (or perhaps *why* you would like to
have the Python infrastructure side with project A over project B,
irrespective of which project is A and which one is B), then perhaps I
can come up with others.
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