modulepath and classpath mixture

[Robert Scholte]

On Tue, 23 Feb 2016 22:14:32 +0100, Jonathan Gibbons  
<jonathan.gibbons at oracle.com> wrote:

>
>
> On 02/23/2016 01:06 PM, Jonathan Gibbons wrote:
>>
>>
>> On 02/23/2016 12:48 PM, Robert Scholte wrote:
>>> On Tue, 23 Feb 2016 01:52:50 +0100, Jonathan Gibbons  
>>> <jonathan.gibbons at oracle.com> wrote:
>>>
>>>>
>>>>
>>>> On 02/22/2016 12:44 PM, Robert Scholte wrote:
>>>>> Hi,
>>>>>
>>>>> first of all I'd like to say that I'm very pleased with the new -mp  
>>>>> options, these matches better with the way Apache Maven would like  
>>>>> to work with jars and class-folders.
>>>>>
>>>>> Here's my use case: I noticed that if I add a module-info to  
>>>>> src/main/java and put all compile-scoped dependencies to the module  
>>>>> path, all compiles fines.
>>>>> I assume that developers are less interested in adding a  
>>>>> module-info.java file to src/test/java, so that's what I'm doing  
>>>>> right now too.
>>>>> Now it seems that I *must* add compile + test scoped to the  
>>>>> *classpath* to be able to compile the test classes.
>>>>> My first approach was to leave the compile-scoped dependencies on  
>>>>> the modulepath and all test-scoped dependencies on the classpath, so  
>>>>> the modules keeps their inner related structure, but it seems that  
>>>>> the classpath classes cannot access the modulepath classes.
>>>>>
>>>>> I'm looking for the confirmation that putting all dependencies on  
>>>>> the classpath is indeed the right approach in this case.
>>>>>
>>>>> thanks,
>>>>> Robert
>>>>
>>>> Robert,
>>>>
>>>> We definitely need some more detailed notes on setting up javac  
>>>> compilations (note to self!) but one thing to note is that by  
>>>> default, the unnamed module (i.e. code on the classpath) only has  
>>>> observability of the modules in the system image. To make modules on  
>>>> the module path observable, you need to use the -addmods option.
>>>>
>>>> -- Jon
>>>
>>> Hi Jonathan,
>>>
>>> this would indeed explain what I'm facing right now. However, adding  
>>> -addmods gives me the following exception:
>>> Caused by: java.lang.IllegalArgumentException: -addmods requires an  
>>> argument
>>>         at  
>>> com.sun.tools.javac.main.Arguments.error(jdk.compiler at 9-ea/Arguments.java:708)
>>>
>>> Is -addmods followed by the same entries as -modulepath or by the  
>>> modulenames. I really hope it is not the latter, because that would  
>>> mean that I first need to discover and read all module-info files.
>>>
>>> thanks,
>>> Robert
>>
>> Sorry, I should have been more explicit.
>>
>> Both javac and java (the launcher) accept an option "-addmods  
>> <module-name>,..." which can be used to name modules to be included in  
>> the module graph.   Confusingly, for javac, the option is listed under  
>> javac -X (that's a bug we will fix), but setting that aside, here's  
>> what the command line help says:
>>
>>   -addmods <modulename>[,<modulename>...] Root modules to resolve in  
>> addition to the initial modules
>>
>> "java -help" says effectively the same.
>>
>>
>> So yes, the option takes a list of module names, not module paths.
>>
>> -- Jon
>>
>>
>>
>
>
>
> ... but that being said, note that you don't have to list all the  
> modules on the module path.    You only need to list root modules, and  
> javac will determine the transitive closure of all the necessary modules.
>
> So, if you're writing tests in the unnamed module, to test a module M,  
> the chances are that you only need "-addmods M".
>

This makes sense. And although I still don't like the fact that this  
requires me to read the module-info, this should be possible for the  
target/mods/m (since it is already compiled).
So my response to Alan was probably a bit too fast.
This requires some tricks on our side to stay compatible with lower Java  
versions while adding some code to read the module-info.

thanks,
Robert


>
> Alan wrote a separate email about different compilation scenarios. Note  
> that in many/most of those cases, no -addmods was necessary.
>
>
> -- Jon


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