module/bootclass troubles with jdk9

[Jonathan Gibbons]

We started 8058150 by looking at @since tags, partly with a view to 
refreshing the tags and making sure they were still up to date, and 
partly with a view to supporting -platform.

But, @since paints an incomplete picture.  Simplistically, one needs to 
construct a file containing the necessary info from previous releases. 
But it is not reasonable to expect rt.jar from previous releases to be 
available when building JDK, so the current thinking is to have some 
sort of text file containing the API specification of earlier releases.

The suggestion to be able to point at a JRE is a new and interesting 
one. Thanks.

-- Jon

On 02/03/2015 12:18 PM, Martin Buchholz wrote:
> 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 <mailto: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
>
>