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
<[email protected] <mailto:[email protected]>> 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
