The JDK 9 module system support for the Javac Task

[tzezula]

Added a support for jigsaw modulepath, upgrademodulepath and modulesourcepath to Javac task. Both single module and multi module compilation is supported.

[bodewig]

This looks a bit more complex than I would have naively expected, I've probably been underestimating the impact of modules.

Many thanks!

[tzezula]

Yes. Unfortunately the javac -modulesourcepath option for the multi module compilation is more complex than existing path arguments. It's described in JEP 261: Module System. The important part is:

In large systems the source code for a particular module may be spread across several different directories. In the JDK itself, e.g., the source files for a module may be found in any one of the directories src//share/classes, src///classes, or build/gensrc/, where is the name of the target operating system. To express this in a module source path while preserving module identities we allow each element of such a path to use braces ({ and }) to enclose commas-separated lists of alternatives and a single asterisk ( * ) to stand for the module name. The module source path for the JDK can then be written as
{src//{share,}/classes,build/gensrc/}

In simple words the javac -modulesourcepath {src/*/{share,<os>}/classes,build/gensrc/*} -d build means that modules will be searched in the src or build/gensrc folders. The java sources of the modules located in the src are in folders share/classes or <os>/classes (relative to module). The java sources of the modules located in build/gensrc are directly in module folder. The path before the * in the path element is a path to module and the path after the * is a path in the module to the actual source root.
During the multi module compilation the javac creates module directories in the build folder containing the module classes.
The Ant Javac task needs to interpret the sourcepath elements to find all modules and their java files to do the up to date check.

For example in a project structure:

src/java.base/share/classes/
src/java.logging/share/classes/
build/java.base/
build/java.logging/

and javac options -modulesourcepath src/*/{share,<os>}/classes -d build the modules are java.base and java.logging. The java.base module has sources in the src/java.base/share/classes/ and is compiled into the build/java.base/ folder. The java.logging module has sources in the src/java.logging/share/classes/ and is compiled into the build/java.logging/ folder. The Ant Javac task needs to do up to date check of sources in src/java.base/share/classes/ (src/java.logging/share/classes/) with classes in build/java.base/ (build/java.logging/).

[bodewig]

Many thanks for the explanation.

[silviuburceadev]

You can use @Test(expected = BuildException.class) instead of useless try/catch.

[bodewig]

Good catch, fixed. Thanks!

[tzezula]

Thanks! I didn't know this.