module/bootclass troubles with jdk9

[Martin Buchholz]

Thanks all for the explanations.

(I don't know where I got "jdk9-b34" from.  Apparently I was using jdk9-b48)

I read JEP 8058150 <http://openjdk.java.net/jeps/8058150> with interest.  I
agree with the goals.  It's nice to be able to compile for a previous
version of the platform with a single flag and without having an actual
copy of the previous jdk available at compile time.  One idea is to promote
javadoc tag @since to be a proper class retention annotation indicating
when that API became available.  This would allow you to implement
-platform N fairly cheaply, and the information would be useful elsewhere.

But ... there has been an increased diversity of java runtimes lately, and
the jigsaw project will only increase that diversity.  I think it will also
be useful to assert that a java compilation is targeting a particular java
runtime (or the intersection of multiple such!) given as a root directory
of an actual JRE, and have javac deduce -source -target and -bootclasspath
from that.  There's a whole javac target constraint algebra behind that!
Difficult.

Also difficult is the distinction between bootmodules and extmodules.

On Tue, Feb 3, 2015 at 10:30 AM, Jonathan Gibbons <
jonathan.gibbons at oracle.com> wrote:

>
> On 02/03/2015 12:17 AM, Alan Bateman wrote:
>
>>
>> For javac then there are other ideas to support compiling for previous
>> releases, Jon might want to say more on this.
>>
>> -Alan
>>
>
> javac is currently in "interim land".  For now, javac still supports the
> bootclasspath family of options, meaning that if you have an rt.jar you
> want to use, you can.  If you don't specify any platform classes, the
> default is to use the classes in the jrt: image.
>
> Going forward, the expectation is that javac will support the JDK 8 set of
> javac path-related options in conjunction with -target N, N <= 8.  In
> addition, the following JEP (currently in Draft state) will explore
> providing a new option -platform N, which will be informally equivalent to
> -source N -target N -bootclasspath jdkN/jre/lib/rt.jar
> http://openjdk.java.net/jeps/8058150
>
> And, we are working on full support for modules in JDK 9 javac, for use
> with -target N, N >= 9.
>
> -- Jon
>