module-info platform dependencies

[Jonathan Gibbons]

On May 14, 2009, at 9:20 PM, Mark Reinhold wrote:

>> Date: Thu, 14 May 2009 13:50:44 -0700
>> From: jonathan.gibbons at sun.com
>
>> Could you (briefly) outline your current ideas regarding platform
>> specification in the module-info file. You alluded to some ideas  
>> when I
>> saw you in your office earlier this week.  If you have a tangible
>> proposal, I'll see what I can do to accomodate it in javac.
>
> Sure.
>
> The basic idea is that the compiler can ask Jigsaw whether a  
> particular
> dependence is upon a known, available platform or profile module,  
> and it
> can also ask what the default is.  If a module-info file declares at
> least one dependence upon a platform module then the compiler does
> nothing.  If it does not declare such a dependence then the compiler
> inserts a dependence upon the default.
>
(snip)
> - Mark

It's not clear to me why the compiler should be doing this and/or its  
not
clear to me what the right policy is here.

It's not clear the compiler should be doing this because so much else  
is being
deferred to the module system, why is this piece of analysis coming  
back into
the compiler?  I'm not saying it shouldn't; I'm just saying I don't  
yet understand
why.

One reason it may be more of a compiler function is future interaction  
with
the compiler's -source and -target flags.  Although rarely used  
correctly,
-target should normally be used in conjunction with -Xbootclasspath.  In
the JDK 8 timeframe, when it may make sense to compile for JDK 7 or  
JDK8,
the -target switch might interact with and/or influence the default of  
the
platform dependence.

If the compiler were to add a default, would you expect it to get  
compiled into
the class file?

It also seems to me that a case can be made for the module system to  
analyze
the need for a default for a group of modules, in that if the set of  
leaf modules
do not unambiguously specify a default, then the module system should  
specify
one for the group. But there should not be a need for anyone (such as  
the
compiler) to insert additional dependences into all modules that don't  
specify
a platform when those modules will have an indirect dependence by  
virtue of
the transitive closure of their own (explicit) dependencies.  That  
sort of group
wide analysis belongs in the module resolver/system, not in the  
compiler.

-- Jon