On Wed, 09 Nov 2016 13:24:02 +0100, Matej Novotny <manov...@redhat.com>
wrote:
Hello,
I was recently trying the following scenario with JDK 9 and mvn compiler
3.6.0:
A new Maven project, with module-info, running with JDK 9, having a
dependency on one other non-modular project (Weld SE in this case).
Feel free to inspect it on GH ->
https://github.com/manovotn/JDK9Playground
Now compiling this with debug mode showed me that Maven puts the
dependency onto module-path of the project.
This means JDK 9 will turn this into automatic module.
So I ended up adding entries (`requires` formulas) into module-info.java
on the one dependency I have there.
I managed to make it compile in the end, but I was wondering about the
following:
=> Is there a way to tell Maven, that I want to add this dependency (and
all it brings in transitively) to CLASSPATH instead of module path?
- that would effectively mean there would be no automatic module (so I
wouldn't need to declare it in module-info) and instead if would "fall
back" to unnamed module (=searching classpath)
Right now there's no simple way to do that. While working on the
modulepath I assumed that once people add the module-info, that they would
also use auto modules by default to get a 100% pure module instead a
hybrid.
I've talked with the jigsaw team and there are still some issues with
transitive (jigsaw) modules, which might effect the current implementation.
I think it is good to track this, so could you add a jira issue at
https://issues.apache.org/jira/browse/MCOMPILER ?
=> Is there a way for Maven to automatically populate your module-info
with entries regarding automatic modules? Or at least some kind of a
detection for which ones do I need?
This is the ever returning question :) So in Java 9 jdeps is capable to
generate a module-info template for you based on the code. It exports all
packages, defines the requires and is often capable to detect which ones
should be transitive, but is cannot detect the optionals. Be aware: this
is a template, something to start with and which you MUST adjust. It is
not an incremental tool.
Maven might create the "requires" part and know the optionals, but it
cannot know about the transitivity (because it jigsaw transitive has a
different definition than Maven transitive. They're still looking for a
better keyword to prevent confusion, so any suggestion is welcome).
However, both Maven and the Jigsaw team need to come with a clear
explanation, because dependencies and modules have different purposes.
I'll give it a try: dependencies resolve into coordinates of multiple
files which will be added to the classpath (and with Java9 it could also
be the module path). Having too much dependencies is not an issue, it is
simply another jar on the path.
The "requires" of the module-info is there to enforce that certain files
are available, either at compile time or at runtime.
So you can compare this as 2 partly overlapping circles. For the larger
part is could be possible, but especially the parts that don't overlap are
hard (impossible?) to identify.
It is very easy to add dependencies, but you never want any irrelevant
"requires" inside your module-info.
I hope you understand that the purpose of dependencies and required
modules are very different. Any attempt to try to solve this with magic is
a potential failure. Any generated file must always be validated by the
developer, there's no 1 to 1 translation.
Robert
Many thanks
Matej
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