Proposal: #AutomaticModuleNames (revised)
forax at univ-mlv.fr
Thu May 4 22:09:20 UTC 2017
Being able to provide stable names as fast as possible for jars will ease the transition toward a modular world.
I'm very pleased by this proposal.
On May 4, 2017 7:38:32 PM GMT+02:00, mark.reinhold at oracle.com wrote:
> #AutomaticModuleNames -- Revise the algorithm that computes the names
> of automatic modules to include the Maven group identifier, when
> available in a JAR file's `pom.properties` file, so that module names
> are less likely to collide, or else drop the automatic-modules feature
> entirely, since it may be more trouble than it's worth. 
> - Do not drop the automatic-modules feature. It's a critical part of
> the overall migration story: It allows application developers to
> get started modularizing their own code without having to wait for
> all of the libraries and frameworks that they use to be modularized.
> Popular libraries and frameworks that are actively maintained will
> hopefully be modularized fairly soon, but less-active projects will
> take longer -- perhaps years or even decades -- and many inactive or
> abandoned projects will never be modularized. This feature has been
> well-received by a wide variety of developers despite the fact that
> some expert users are not comfortable with it.
> - Define a JAR-file manifest attribute, `Automatic-Module-Name`, whose
> value is used as the name of the automatic module defined by that JAR
> file when it is placed on the module path, as previously suggested
> . If a JAR file on the module path does not have such a
> manifest attribute then its automatic-module name is computed using
> the existing filename-based algorithm.
> The name of this attribute is now `Automatic-Module-Name` rather than
> `Module-Name`. The former makes it clear that if a JAR file on the
> module path contains both an `Automatic-Module-Name` manifest
> attribute and an explicit `module-info.class` file then the manifest
> attribute is irrelevant, because the module defined by the JAR file
> is explicit rather than automatic. `Module-Name` would also suggest
> that there are `Module-Exports` and `Module-Requires` attributes,
> which there are not.
> With this mechanism a library maintainer can claim a stable module
> name with very little effort; in Maven, e.g., a manifest attribute
> can be added in just a few lines of a project's `pom.xml` file. A
> library maintainer can claim a stable name early, before all of the
> library's dependencies are modularized, which will allow libraries
> and applications that depend upon it to be modularized immediately.
> A user of a library can suggest a stable name to the library's
> maintainer, and easily submit a patch that implements it. This will
> enable the uncoordinated modularization of libraries across the
> entire ecosystem.
>- Strongly recommend that all modules be named according to the reverse
> Internet domain-name convention. A module's name should correspond
> to the name of its principal exported API package, which should also
> follow that convention. If a module does not have such a package, or
> if for legacy reasons it must have a name that does not correspond to
> one of its exported packages, then its name should at least start
> with the reversed form of an Internet domain with which the author is
> - Make sure that developers are aware of the risks of publishing, for
> broad use, explicit modules that require automatic modules. An
> automatic module is unreliable, since it can depend on types on the
> class path, and its name and exported packages could change if and
> when it's converted into an explicit module. It's fine to declare
> and use explicit modules that require automatic modules in limited
> settings. If you publish such a module to, e.g., Maven Central, then
> you must be prepared to revise both the declaration and content of
> your module as its dependencies are modularized over time. This may
> have an adverse impact on the users of your module, especially if
> your module `requires transitive` an automatic module.
>The following three points are essentially unchanged from the first
> - Do not revise the algorithm that computes the names of automatic
> modules. The suggestion to use Maven coordinates when available 
> would help less than half of the most popular projects in use today,
> as determined by three different surveys. It would result in module
> names that are often annoyingly verbose and known to be objectionable
> to some module authors, and it would raise non-trivial issues with
> regard to standardization and convention. The names generated by the
> current algorithm do not follow the reverse-DNS convention, but they
> are at least easily derivable from the name of the original JAR
> files. 
> - To increase awareness of when automatic modules are used, and of the
> consequences of their use, suggest that Java language compilers issue
> two new types of warnings, and implement these warnings in the RI:
> - An opt-in (i.e., off-by-default) warning on a reference to
> an automatic module in a `requires` directive in a module
> declaration, and
> - An opt-out (i.e., on-by-default) warning on a reference to
> an automatic module in a `requires transitive` directive in
> a module declaration.
> The first warning allows developers to be maximally hygienic if they
> so choose. The second helps make the author of an explicit module
> aware that they're putting the users of that module at risk by
> establishing implied readability to an automatic module.
> - Encourage Java run-time systems to make it easy to identify via,
> e.g., command-line options, which observable modules are automatic,
> which observable modules would establish implied readability to
> automatic modules if resolved, and which automatic observable modules
> are actually resolved. Implement these capabilities in the RI.
>This revised proposal is informed by a vigorous discussion on the
>jigsaw-dev mailing list  of the first proposal . Two things
>clear in that discussion, and in related discussions triggered by it.
>First, after twenty years the reverse-DNS naming convention is deeply
>ingrained in the minds of most Java developers. Stephen Colebourne
>a clear and passionate case for it  and many developers voiced
>for his argument, both on Twitter and elsewhere. Some people may
>shorter, project-oriented names, and those can be fine to use in
>projects that will never, ever see the light of day outside of a single
>organization. If you create a module that has even a small chance of
>being open-sourced in the future, however, then the safest course is to
>choose a reverse-DNS name for it at the start.
>Second, the fact that the name and effective API of an automatic module
>are inherently unstable is less of a problem than I previously thought
>[a]. Developers who use Maven and related tools, such as Gradle --
>which is most developers -- are used to coping with breakage when they
>upgrade the dependencies of a project to a newer version [b][c]. If
>name or effective API of an automatic module change, either when its
>maintainer adds an `Automatic-Module-Name` attribute or writes an
>explicit `module-info.java` file, then the maintainers of projects that
>use that module will just fix any problems that they encounter when
>After thinking about the first observation I'm now convinced that if
>tools insert `Automatic-Module-Name` manifest attributes then they will
>only do so when the module names that they define follow the
>convention, since to do otherwise would go against what most developers
>strongly prefer and expect. After thinking about that and the second
>observation I hereby retract [d] my previous advice  that automatic
>modules should not be given stable names.
> * * *
>In related threads on jigsaw-dev both Stephen Colebourne [e] and Robert
>Scholte [f] suggest a new kind of explicit module, variously called
>"partial" or "incomplete" or "soft", which can read all unnamed modules
>so that dependencies that have not yet been modularized can be left on
>the class path. This is an attractive notion on the surface, and in
>one that we partly implemented in the prototype code base over two
>ago, using the term "loose". We didn't pursue it then, however, and I
>don't think it's worth pursuing now, for two reasons:
> - If "partial" (or whatever) modules were to replace automatic modules
> then application developers would have to wait until all of their
> dependencies have been at least "partially" modularized before they
> can even begin to experiment with modularizing their own code.
> - We could solve that by keeping automatic modules and adding partial
> modules, but then we'd have a more complex module system and a more
> complex story to tell. To consider just one possible question,
> should developers go ahead and use their dependencies as automatic
> modules, or wait for them to become named automatic modules, or wait
> for them to become partial modules?
>The `Automatic-Module-Name` manifest attribute is, from a technical
>standpoint, aesthetically unpleasant since it defines a second way
>to name modules. Taken alone, however, it does enable uncoordinated
>modularization using stable module names with little effort, and so
>it appears to be the least-bad option on the table.
Sent from my Android device with K-9 Mail. Please excuse my brevity.
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