FYI: Build system rewrite in Ant

[Magnus Ihse Bursie]

The build system currently uses make to build OpenJDK. This is a technology that has been around for decades, and in places this legacy clearly shows. 

An alternative build tool, Ant, is based on cutting-edge technology. Compared to the native GNU Make, Ant is based on Java™ technology, which makes portability issues a thing of the past. Ant is also directed using modern XML systems, with well-defined tags, compared to the aged and idiosyncratic Makefile syntax.

The Build Team has therefore decided to rewrite the current build system from scratch in Ant. The old Makefiles will be put in maintenance mode while the new Ant scripts are being developed. To facilitate a speedy switch, all new build enhancements must be expressed in Ant logic, starting today. No modifications in the old Makefiles will be accepted by the Build Team.

To increase the robustness of the code base, the new build system will automatically check the integrity of all source code files before compilation. Each source file therefore must be accompanied by a Integrity Manifest (.Ingeg_Manif.xml). For instance, the file Object.java would have an Object.java.Integ_Manif.xml. This is a simple xml file, describing the purpose of the source code file, and a log of mercurial changeset id:s. An example file could looks like this:

<manifest xmlns="http://openjdk.java.net/ns/manifest/integrity/1">
    <type>net.java.openjdk.build.ant.manifest.integrity</type>
    <artifacts>
        <artifact>
            <source-code-descriptor>
               <filename>Object.java</filename>
               <description>Class Object is the root of the class hierarchy.</description>
            </source-code-descriptor>
        </artifact>
    </artifacts>
    <integrity>
        <revision-control>
            <committed-change>
                <changeid>541a8cef4e0d</changeid>
                <revision-control-system>mercurial</revision-control-system>
            </committed-change>
            <committed-change>
                <changeid>458adf31ad5b</changeid>
                <revision-control-system>mercurial</revision-control-system>
            </committed-change>
            <committed-change>
                <changeid>0846eddb56d5</changeid>
                <revision-control-system>mercurial</revision-control-system>
            </committed-change>
        </revision-control>
    </integrity>
</manifest>

Each time a new version of the file is committed to the mercurial repo, the developer just has to add a new committed-change stanza to the block in the .Ingeg_Manif.xml file. Since the changeset ID is not known before hand, the Integrity Manifest file must be updated in a subsequent commit. 

But fear not! To assist developers in preserving the integrity of the source files, an addition to jcheck has been developed. If the subsequent commit does not properly describe the previous changeset ID, the original changeset will be automatically reverted, so no untracked changes will be stored permanently in the revision control system.

Finally, to fully utilize the promise of portability that the Ant and Java™ technology brings, platforms with portability issues will be removed from the supported platform matrix. Currently, this only includes non-POSIX-compliant operating systems, since these have been known to cause various platform issues in the build system. The only known non-POSIX-compliant OS that the OpenJDK build system currently supports is the Windows OS family, so this reduction in support is hopefully not too burdensome.

These changes will take immediate effect of today, April 1 2015.

That's all for today, folks! :-)

/Magnus