Use-cases for version ranges?

[David Bosschaert]

I think that the fact that in JBoss Modules the metadata is *outside*
of the module (in a separate file that sits alongside the module) and
in OSGi the metadata is *inside* the module (embedded in the Jar) is a
significant difference.

If you have the metadata outside of the module you have additional
flexibility. You can change the metadata without changing the module
itself, so if there is an issue with the metadata you can easily fix
it up (e.g. if you need to depend on another version of your
dependency). Also there are obviously impacts of changing the module
metadata if its inside the module and you are working with signed
jars. On the other side, having the metadata inside the module has the
benefit that you only need to worry about a single artifact: the
module itself.

I'm not advocating one over the other here; I think both have
benefits, but I think that using version ranges makes more sense in
the case the metadata is embedded in the module.

If I'm not mistaken, the model that Jigsaw is going for is currently
also the model where the metadata is inside the module.

David

On 21 November 2011 16:33, David M. Lloyd <david.lloyd at redhat.com> wrote:
> On 11/21/2011 10:11 AM, Neil Bartlett wrote:
>>
>> David,
>> I'm likewise tired of hearing these defeatist straw-man arguments.
>> First, nobody is suggesting that you be forced to use version ranges.
>> Second, nobody is suggesting that you be forced to design software by
>> separating interfaces from implementation. Finally, nobody is
>> suggesting that unmodified legacy code can be trivially modularised in
>> *any* module system.
>
> Trivial?  Depends on how you define it.  Most artifacts should be able to be
> modularized as-is however, with minimal changes if any.  We adopted an
> external descriptor strategy for the sole purpose of being able to use
> modules as is, and we were able to package our 200+ modules just that way,
> no repackaging needed.  So far the only problems we have really run into
> seem to be legitimate bugs, and one or two libraries which assume a flat
> classpath.
>
> I just glanced at the quick stats for Maven Central.  There are 267,924
> indexed artifacts at the time of this writing - 31,847 unique artifacts.
>  This is a major reason why people even use Java in the first place. Ideally
> we would be able to start with at least the possibility of having a somewhat
> pre-populated repository.
>
>> The module system must support both existing software and new
>> software, of course. You seem suggest that I believe existing software
>> is unimportant; nothing could be further from the truth. But I also
>> believe that new software is important and that practices like
>> interface/implementation separation and semantic versioning will help
>> make the new software better than the old software.
>> Therefore I believe that these features must be supported (though not
>> mandated) in any new module system. You appear to be suggesting that
>> these features are worthless because they cannot be applied to
>> existing software, and/or will not be used by all Java developers.
>> Well so what??
>
> Not worthless, but a question of personal choice.  I believe that interface
> and implementation separation has not been objectively shown to be a
> superior way to write frameworks.  In my experience, sometimes it is and
> sometimes it is not.
>
> I believe that "semantic versioning" isn't going to work because most people
> who develop Java software will not understand it or not get it right, due in
> no small part to being a complex idea with a lot of subtlety.  In think that
> empirical testing is the only way to ensure compatibility which will scale.
>
>> Regards,Neil
>> On Mon, Nov 21, 2011 at 3:15 PM, David M. Lloyd<david.lloyd at redhat.com>
>>  wrote:
>>>
>>> I'm tired of hearing pie-in-the sky, "intro to OOP" wishful crap like
>>> this.
>>>  Mission one should be supporting *existing* code.  The fact is that
>>> people
>>> do *not* always split their API from their implementation, and APIs
>>> almost
>>> *never* consist solely of interfaces.  There are many ways of designing
>>> an
>>> API which people consider "right" and I don't see anyone on this list
>>> having
>>> any special insight that would enable them to select the "one true"
>>> approach
>>> to API design.
>>>
>>> The fact is that any version scheme or module resolution engine which
>>> only
>>> works for new code which is designed "properly" for it is *going* to
>>> fail.
>>>  And there's no reason for such constraints anyway.  Version ranges are
>>> barely useful at all in practice.  The only ones who can assert
>>> compatibility between two libraries of arbitrary version are the ones who
>>> have tested the two together (along with anything else that uses a
>>> combination of the two).
>>>
>>> The best one can do establish *minimum* compatibility based on available
>>> features, and test test test.  When a module is added to a repository, if
>>> it
>>> is tested by running both its internal unit tests and all available tests
>>> of
>>> all its dependents, then that should be adequate to establish
>>> compatibility
>>> *within a repository*.  There are too many factors to establish
>>> compatibility beyond it.
>>>
>>> On 11/20/2011 07:45 AM, Neil Bartlett wrote:
>>>>
>>>> Stephen,
>>>>
>>>> You again seem to be talking about dependencies on implementation
>>>> packages. If we depend on APIs consisting primarily of interfaces,
>>>> then versions and version ranges are reliable and can be completely
>>>> automated.
>>>>
>>>> Regards,
>>>> Neil
>>>>
>>>>
>>>> On Sun, Nov 20, 2011 at 12:25 PM, Stephen McConnell<mcconnell at dpml.net>
>>>>  wrote:
>>>>>
>>>>> I could say that the question is academic - but here is the thing - its
>>>>> not
>>>>> even academic.
>>>>>
>>>>> We talk about versions and yet the platform has no computational
>>>>> mechanisms
>>>>> to flag version violation. At least an academic discussion would bring
>>>>> in
>>>>> grounded metrics.  In reality - the discussion here about V1 versus V2
>>>>> and
>>>>> that warm fuzzy feeling when your are just a n.m from an n+1 and it's a
>>>>> waste of breath (and that comment goes to all sides of the debate).
>>>>>
>>>>> Give me an endorsed tool that shows me that module [name]-[build] is
>>>>> computationally backward compatible to a different [name]-[build] and
>>>>> then,
>>>>> only them will this discussion have reasonable grounds to assert any
>>>>> authority on the subject of version compatibility (past or future).
>>>>> Without
>>>>> that tool - versioning is a unqualified statement of trust. And the
>>>>> evidence
>>>>> suggests that the threshold of trust delivery on actual computational
>>>>> compliance is really really thin.
>>>>>
>>>>> Cheers, Steve.
>>>>>
>>>>>
>>>>> -----Original Message----- From: cowwoc
>>>>> Sent: Sunday, November 20, 2011 1:39 PM
>>>>> To: jigsaw-dev at openjdk.java.net
>>>>> Subject: Re: Use-cases for version ranges?
>>>>>
>>>>>
>>>>>    I'd like to propose another possibility: the author of the
>>>>> dependency should tell *us* about version compatibility, not the other
>>>>> way around. For example:
>>>>>
>>>>> 1. The author of module A declares a dependency on module B version 1.2
>>>>> (specific version).
>>>>> 2. The author of module B publishes version 1.3. He declares that
>>>>> version 1.3 is compatible with 1.2 (meaning, the runtime system is
>>>>> allows to substitute version 1.3 for 1.2).
>>>>>
>>>>>    The upside of this approach is that the author of B is in a better
>>>>> position to declare compatibility than the author of A. The author of A
>>>>> still only needs to test a single version. What do you think?
>>>>>
>>>>> Gili
>>>>>
>>>>> On 19/11/2011 1:59 AM, Neil Bartlett wrote:
>>>>>>
>>>>>> Gili,
>>>>>>
>>>>>> I didn't say anything about guarantees, and in this industry I have
>>>>>> never heard of anybody providing a guarantees about the performance of
>>>>>> their software, especially in the presence of external dependencies.
>>>>>>
>>>>>> Version ranges are a means of communicating expectations, and we
>>>>>> provide both a lower and an upper bound because this is useful
>>>>>> information. I expect my module will work with 1.2.14, and I expect it
>>>>>> will not work with 2.0. If I were a provider of the API rather than a
>>>>>> consumer then I would have a much narrower expectation,  e.g.
>>>>>> [1.2,1.3), and this would also be useful information to convey.
>>>>>>
>>>>>> Regards
>>>>>> Neil
>>>>>>
>>>>>> On Sat, Nov 19, 2011 at 4:27 AM, cowwoc<cowwoc at bbs.darktech.org>
>>>>>>  wrote:
>>>>>>>
>>>>>>> Neil,
>>>>>>>
>>>>>>>    I guess I don't understand why Jigsaw should work differently from
>>>>>>> Maven
>>>>>>> on this point. I am expecting developers to specify specific versions
>>>>>>> that
>>>>>>> they tested (point versions, not ranges) and end-users may override
>>>>>>> these
>>>>>>> "recommendations" as they see fit.
>>>>>>>
>>>>>>>    Where you see version range [1.2.14, 2.0) as a way of
>>>>>>> communicating
>>>>>>> "the
>>>>>>> developer guarantees 1.2.14 but you may use newer versions up to 2.0
>>>>>>> at
>>>>>>> your
>>>>>>> own risk" I'd expect the developer to simply specify 1.2.14 and there
>>>>>>> should
>>>>>>> be no limit on what version end-users may use if they so wish.
>>>>>>>
>>>>>>> Gili
>>>>>>>
>>>>>>> On 18/11/2011 2:23 AM, Neil Bartlett wrote:
>>>>>>>>
>>>>>>>> I noticed that I failed to address your point about Maven using
>>>>>>>> point
>>>>>>>> versions.
>>>>>>>>
>>>>>>>> Maven is a build tool. At build time we need to compile against a
>>>>>>>> single specific version so that we have repeatable builds. In
>>>>>>>> general
>>>>>>>> we should build each module against the lowest version of the
>>>>>>>> library
>>>>>>>> that it can possibly use, and there are no major negative
>>>>>>>> consequences
>>>>>>>> of having several versions of a library at build time (except that
>>>>>>>> Maven has to download a lot!). At runtime however we need to have
>>>>>>>> the
>>>>>>>> flexibility to substitute a single compatible version.
>>>>>>>>
>>>>>>>> Neil
>>>>>>>>
>>>>>>>> On Fri, Nov 18, 2011 at 7:10 AM, Neil Bartlett<njbartlett at gmail.com>
>>>>>>>>  wrote:
>>>>>>>>>
>>>>>>>>> Suppose as the developer of module A, I declare a dependency on
>>>>>>>>> log4j,
>>>>>>>>> exactly version 1.0.0 because I have not tested against log4j
>>>>>>>>> 1.0.1,
>>>>>>>>> 1.0.2, 1.3, 999.999 etc. I effectively prevent my module *ever*
>>>>>>>>> being
>>>>>>>>> used with log4j version 1.0.1 even if this combinations is later
>>>>>>>>> tested and proven to work by somebody else. In other words, testing
>>>>>>>>> is
>>>>>>>>> important but it doesn't necessarily have to always be done by the
>>>>>>>>> original developer of each module.
>>>>>>>>>
>>>>>>>>> On the other hand let's say I state my dependency using the
>>>>>>>>> following
>>>>>>>>> range: [1.2.14, 2.0). This is OSGi syntax and I believe Jigsaw is
>>>>>>>>> following it, and it simply means I accept version 1.2.14 up to but
>>>>>>>>> not including 2.0. Anybody can see that I compiled and tested
>>>>>>>>> against
>>>>>>>>> 1.2.14, but has the option of using 1.2.15, 1.2.16, 1.3, 1.9 etc.
>>>>>>>>> It
>>>>>>>>> does not mean that I *guarantee* my module will work with log4j 1.3
>>>>>>>>> because that obviously depends on whether the log4j authors accept
>>>>>>>>> and
>>>>>>>>> follow the common semantics of indicating backwards-incompatible
>>>>>>>>> changes with a bump to the first version segment.
>>>>>>>>>
>>>>>>>>> The consequence of trying to lock down imports to a narrow range or
>>>>>>>>> even a point version is that assembling an application becomes very
>>>>>>>>> difficult, and we are forced to deploy many versions of common
>>>>>>>>> libraries concurrently. This is non-optimal, though we can handle
>>>>>>>>> it
>>>>>>>>> to some degree via per-module classloaders as in OSGi.
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Neil
>>>>>>>>>
>>>>>>>>> On Thu, Nov 17, 2011 at 11:52 PM, cowwoc<cowwoc at bbs.darktech.org>
>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> Can someone please explain why modules need to be able to specify
>>>>>>>>>> version
>>>>>>>>>> ranges for dependencies? I believe OSGI allows the specification
>>>>>>>>>> of
>>>>>>>>>> version
>>>>>>>>>> ranges while Maven allows the specification of individual
>>>>>>>>>> versions.
>>>>>>>>>>
>>>>>>>>>> The only thing that comes to mind is when module C depends on A
>>>>>>>>>> and
>>>>>>>>>> B,
>>>>>>>>>> A
>>>>>>>>>> depends on log4j 1.0, and B depends on log4j 1.1. What does C do?
>>>>>>>>>> Is
>>>>>>>>>> this
>>>>>>>>>> the main use-case for version ranges?
>>>>>>>>>>
>>>>>>>>>> By the sound of it, this is a trust model where developers are
>>>>>>>>>> told
>>>>>>>>>> that
>>>>>>>>>> log4j 1.x won't break compatibility so they depend on that range
>>>>>>>>>> without
>>>>>>>>>> actually testing against each version (newer versions may be
>>>>>>>>>> released
>>>>>>>>>> after
>>>>>>>>>> their own software). I question whether such a mechanism is better
>>>>>>>>>> or
>>>>>>>>>> worse
>>>>>>>>>> than depending on individual versions which may be overridden at a
>>>>>>>>>> later
>>>>>>>>>> time (a la Maven). On the one hand, you don't need to release a
>>>>>>>>>> new
>>>>>>>>>> version
>>>>>>>>>> of the application each time a dependency is updated. On the other
>>>>>>>>>> hand,
>>>>>>>>>> no
>>>>>>>>>> one is actually running tests to ensure that the versions are
>>>>>>>>>> really
>>>>>>>>>> compatible.
>>>>>>>>>>
>>>>>>>>>> Is there a way to get module A to see log4j 1.0 and module B to
>>>>>>>>>> see
>>>>>>>>>> log4j
>>>>>>>>>> 1.1 (using separate ClassLoaders)?
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> Gili
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> View this message in context:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> http://jigsaw-dev.1059479.n5.nabble.com/Use-cases-for-version-ranges-tp5002801p5002801.html
>>>>>>>>>> Sent from the jigsaw-dev mailing list archive at Nabble.com.
>>>>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>
>>>
>>> --
>>> - DML
>>>
>
>
> --
> - DML
>