[Distutils] Upcoming changes to PEP 426/440

[Gabriel de Perthuis]

On Sun, 30 Jun 2013 21:21:54 +1000, Nick Coghlan wrote:
> On 30 June 2013 18:53, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:
>> Nick Coghlan <ncoghlan <at> gmail.com> writes:
>>
>>> No, because the semantic dependencies form a Cartesian product with
>>> the extras. You can define :meta:, :run:, :test:, :build: and :dev:
>>> dependencies for any extra. So if, for example, you have a "localweb"
>>> extra, then you can define extra test dependencies for that.
>>>
>>> The semantic specifiers determine *which sets of dependencies* you're
>>> interested in, while the explicit extras define optional subsets of
>>> those.
>>
>> Isn't that the same as having an additional field in the dependency mapping?
>> It seems like that's how one would organise it at the RDBMS level, anyway.
>>
>> {
>>   "install": "localweb-test-util [win] (>= 1.0)",
>>   "extra": "localweb",
>>   "environment": "sys_platform == 'win32'",
>>   "kind": ":test:"
>> }
> 
> You certainly *could* define it like that, but no existing dependency
> system I'm aware of does it that way. If they allow for anything other
> than runtime dependencies in the first place, they define a different
> top level field:
> 
> * setuptools has requires and install_requires
> * PEP 346 has Requires-Dist and Setup-Requires-Dist
> * RPM has Requires and BuildRequires
> * npm has dependencies and devDependencies

At least for Debian, and probably RPM, source dependencies have a
different field name because they are carried by a source package
rather than a binary one.  The nature of the dependencies isn't
different, the required packages are binary in both cases.

The cartesian product might be overkill.  If someone elects to install
development dependencies I don't see a point in picking and choosing.
There's enough support noise when people fail to build from source,
and while an author is knowledgeable and might conceive more than one
way to set things up, publishing them would cause more trouble than
it's worth.

So it would prefer that dev and test be extras with well known names,
so that dev, test, and any other extras define dependencies with a
minimum of ambiguity and without the need for a second level of
qualifiers.